Interim Report
Wireless Repeater, Pico-BTS, WLAN
and W-PBX
Ian F. Akyildiz
Broadband and Wireless Networking Laboratory
School of Electrical and Computer Engineering
Georgia Institute of Technology
Atlanta, GA 30332
Email: ian@ee.gatech.edu
Tel: (404) 894-5141; Fax: (404) 894-7883
Executive Summary
Wireless technology is the solution to fulfill people’s desire to communicate from
anywhere and at anytime. Compared to wire-line schemes, they have many advantages
such tether-less communication, easy deployment, and low cost. The existing schemes of
wireless local area communication can provide wireless services to end users to some
extent of satisfaction. However, considering the ever-increasing demands for high speed,
QoS, and global mobility of multimedia services, a new approach to wireless area
communication is needed.
In order to succeed in the fierce competition of the Wireless market, it is
imperative for a leader like KTICOM to adapt the recent most technologies in this area.
The report concerns KTICOM and its attempts to develop a new approach to the next
generation wireless communication in local areas. Typical existing local area wireless
communication alternatives such as repeater, pico-BTS, WLAN, and WPABX are
investigated individually. Such investigation mainly consists of technology analysis,
target market forecast, technology development prospect analysis, network integration,
service analysis, network design plan, network deployment scenarios, and network costs
analysis.
The typical alternatives of wireless local area communications are also compared
from the perspectives such as services, technical characteristics, costs, market, and
network deployment scenarios.
To meet the goal of high speed, QoS guarantees, and global mobility of the next
generation wireless communication networks, launching a project to develop new
products for wireless local area communication is highly motivated. Such a project can be
accomplished with solutions that have great potentials of market penetration capability.
1
CONTENTS
EXECUTIVE SUMMARY
INTRODUCTION
1.
1
7
WIRELESS REPEATER 8
1.1.
OVERVIEW ................................................................................................................................... 8
1.2.
TECHNOLOGY, STANDARDIZATION, PRESENT CONDITIONS OF REPEATERS ................................10
1.2.1. The Repeater Technology and Standards ..............................................................................10
1.2.2. Current Use of Repeaters and Industry Practices .................................................................13
1.2.3. Detailed System Analysis of the Repeater Technology ..........................................................16
1.2.4. Interference to Repeaters .......................................................................................................17
1.2.5. Environmental Issues .............................................................................................................18
1.2.6. Major Suppliers of the Repeater Products.............................................................................19
1.3.
REPEATER TYPES AND THEIR CHARACTERISTICS ........................................................................19
1.4.
MAIN TARGET MARKET FORECAST ............................................................................................21
1.4.1. Current Market Segments and Their Penetration ..................................................................22
1.4.2. A Forecast of the Target Markets and Estimated Market Size ..............................................22
1.5.
TECHNOLOGY DEVELOPMENT PROSPECT ANALYSIS ...................................................................23
1.6.
SERVICE ANALYSIS .....................................................................................................................24
1.7.
NETWORK DESIGN PLAN ANALYSIS ............................................................................................24
1.8.
IN-BUILDING NETWORK DESIGN ALTERNATIVES USING THE REPEATER TECHNOLOGY .............25
1.8.1. Coverage and Capacity Analysis as Part of the Network Design Process ............................27
1.9.
NETWORK DEPLOYMENT TECHNOLOGY AND PREMISE NETWORK SECURITY PLAN ....................28
1.10.
NETWORK DEPLOYMENT SCENARIOS..........................................................................................28
1.11.
NETWORK COST ANALYSIS ..........................................................................................................29
1.12.
CONCLUSIONS .............................................................................................................................31
2.
PICO-BTS
32
2.1.
OVERVIEW ..................................................................................................................................32
2.2.
TECHNOLOGY AND STANDARDIZATION OF PICO-BTS .................................................................32
2.2.1. Characteristics and Advantages ............................................................................................32
2.2.2. Components and functionality ...............................................................................................33
2.2.3. Current Progress of Pico-BTS ...............................................................................................34
2.2.4. Standardization......................................................................................................................35
2.2.5. Frequency Allocation.............................................................................................................35
2.2.6. Power Management ...............................................................................................................36
2.2.7. Interference ............................................................................................................................36
2.2.8. Environmental Conditions .....................................................................................................38
2.2.9. Major Suppliers and Products ...............................................................................................38
2.3.
TYPES OF PICO-BTS ....................................................................................................................39
2.4.
MAIN TARGET MARKET FORECAST ............................................................................................39
2.4.1. Discussion of the Current Market Segments ..........................................................................40
2.4.2. A Forecast of the Target Markets and Estimated Market Size ..............................................40
2.5.
HEALTH AND SAFETY..................................................................................................................40
2.6.
TECHNOLOGY DEVELOPMENT PROSPECT ANALYSIS ...................................................................41
2.7.
SERVICE ANALYSIS .....................................................................................................................43
2.7.1. Current Services (2.5G/3G) ...................................................................................................44
2.7.2. Future Services ......................................................................................................................44
2.8.
NETWORK DESIGN PLAN ANALYSIS ............................................................................................45
2.8.1. Distributed Antenna Approach ..............................................................................................45
2.8.2. Distributed BTS Approach .....................................................................................................47
2.9.
NETWORK SECURITY PLAN .........................................................................................................48
2
2.10.
2.11.
2.12.
3.
NETWORK DEPLOYMENT SCENARIOS AND ANALYSIS .................................................................48
NETWORK COST ANALYSIS .........................................................................................................49
CONCLUSIONS .............................................................................................................................50
WIRELESS LAN51
3.1.
OVERVIEW ..................................................................................................................................51
3.2.
TECHNOLOGY, STANDARDIZATION, PRESENT CONDITIONS OF WLAN .......................................52
3.2.1. The WLAN Technology and Standards ..................................................................................52
3.2.2. Current Use of WLAN and Industry Practices ......................................................................62
3.2.3. Working Frequency, Typical Bandwidth, and Propagation Footprints of WLAN .................63
3.2.4. Interference to WLANs ..........................................................................................................64
3.2.5. Environmental Issues .............................................................................................................66
3.2.6. Major Suppliers of the WLAN Products ................................................................................67
3.3.
WLAN TYPES AND THEIR CHARACTERISTICS ............................................................................69
3.4.
MAIN TARGET MARKET FORECAST ............................................................................................72
3.4.1. Current Market Segments and Their Market Penetration .....................................................72
3.4.2. A Forecast of the Target Markets and Estimated Market Size ..............................................74
3.5.
TECHNOLOGY DEVELOPMENT PROSPECT ANALYSIS ...................................................................74
3.6.
INTERWORKING/INTEGRATION WITH IMT-2000..........................................................................75
3.7.
SERVICE ANALYSIS .....................................................................................................................77
3.8.
NETWORK DESIGN PLAN ANALYSIS ............................................................................................77
3.8.1. Description of Possible In-Building Network Design Alternatives using the WLAN
Technology and possible external interference/interoperability ..........................................................81
3.8.2. Coverage and Capacity Analysis as a part of Network Design Process ...............................81
3.9.
NETWORK DEPLOYMENT TECHNOLOGY AND PREMISE NETWORK SECURITY PLAN ....................81
3.10.
NETWORK DEPLOYMENT SCENARIOS..........................................................................................83
3.11.
NETWORK COST ANALYSIS .........................................................................................................84
3.11.1.
Identification of the cost of various components involved in Wireless LAN setup ............84
3.11.2.
Analysis of the total Economics Involved in Deploying and Running such WLANs .........85
3.12.
CONCLUSIONS .............................................................................................................................85
4.
WIRELESS PBX 86
4.1.
OVERVIEW ..................................................................................................................................86
4.2.
TECHNOLOGY ANALYSIS.............................................................................................................86
4.2.1. Current Technology of WPBX ...............................................................................................86
4.2.2. The Frequency Bands ............................................................................................................88
4.2.3. Products by Leading Vendors ................................................................................................88
4.3.
CHARACTERISTIC ANALYSIS .......................................................................................................89
4.4.
MAIN TARGET MARKET DEDUCTION ..........................................................................................90
4.4.1. Current Wireless PBX Market Segments ...............................................................................90
4.4.2. Market Forecast ....................................................................................................................90
4.5.
TECHNOLOGY DEVELOPMENT PROSPECT ANALYSIS ...................................................................91
4.6.
INTERWORKING / INTEGRATION TECHNOLOGY ANALYSIS WITH IMT-2000 ................................92
4.7.
SERVICE ANALYSIS .....................................................................................................................93
4.8.
NETWORK DESIGN PLAN ANALYSIS ............................................................................................94
4.8.1. Wireless Telephone Solution for Mobile Communication in the Workplace .........................95
4.8.2. Wireless Voice and Data Solutions Over Local Area Networks ............................................97
4.9.
SECURITY ....................................................................................................................................99
4.10.
NETWORK DEPLOYMENT SCENARIOS..........................................................................................99
4.11.
NETWORK COST ANALYSIS .......................................................................................................100
5.
COMPARISON OF WIRELESS REPEATER AND PICO-BTS
102
5.1.
COMPARATIVE SERVICE ANALYSIS ...........................................................................................102
5.2.
TECHNICAL CHARACTERISTIC COMPARISON AND ANALYSIS ....................................................103
5.2.1. Cost Comparison and Analysis ............................................................................................104
5.2.2. Comparison and Analysis of Main Markets and Network Deployment ...............................105
3
6.
COMPARISON OF WLAN AND WPBX
6.1.
6.2.
6.3.
6.4.
7.
107
COMPARATIVE SERVICE ANALYSIS ...........................................................................................107
TECHNICAL CHARACTERISTIC (CAPACITY AND COVERAGE) COMPARISON AND ANALYSIS.........108
COST COMPARISON ...................................................................................................................109
MARKETS AND NETWORK DEPLOYMENT COMPARISON ............................................................109
COMPARISON OF PICO-BTS AND WLAN/WPBX
7.1.
7.2.
7.3.
7.4.
8.
111
COMPARATIVE SERVICE ANALYSIS ...........................................................................................111
TECHNICAL CHARACTERISTICS COMPARISON AND ANALYSIS ..................................................113
COST COMPARISON AND ANALYSIS ..........................................................................................114
COMPARISONS AND ANALYSIS OF MAIN TARGET MARKETS AND NETWORK DEPLOYMENTS ...115
IN-BUILDING DEPLOYMENT
118
8.1.
TAKING ADVANTAGE OF TECHNOLOGICAL EVOLUTION AND MEETING CUSTOMER DEMANDS....118
8.2.
NETWORK DEPLOYMENT SCENARIO (TECHNOLOGY, MARKET, ARCHITECTURE,
IMPLEMENTATION PHASES, SCHEDULE, RESOURCE ESTIMATES) .............................................................120
8.2.1. Wireless PBX System deployment for corporate..................................................................120
8.2.2. WLAN internetworking with Wired Network .......................................................................121
8.2.3. Unified 3G Wireless Network ..............................................................................................122
8.2.4. Complementary Technologies of cdma2000 and 802.11 .....................................................123
8.2.5. VPN security for Wireless Communication .........................................................................124
8.2.6. HiperLAN/2 deployment for Corporate LAN .......................................................................125
9.
CONCLUSION 127
10.
REFERENCES 128
4
LIST OF FIGURES
FIGURE 1. WIRELESS REPEATER .....................................................................................................................11
FIGURE 2. MULTIPLE TRANSMITTER NETWORKS ............................................................................................12
FIGURE 3. MULTIPLE REPEATER NETWORKS ...................................................................................................12
FIGURE 4. WIRELESS NETWORK WITHIN A SINGLE CELL .................................................................................26
FIGURE 5. WIRELESS NETWORK USING REPEATERS ........................................................................................26
FIGURE 6. WIRELESS REPEATER .....................................................................................................................30
FIGURE 7. MAJOR COMPONENTS OF A PICO-BTS ............................................................................................33
FIGURE 8. IP RADIO ACCESS WIRELESS NETWORK ..........................................................................................43
FIGURE 9. IN-BUILDING NETWORK .................................................................................................................45
FIGURE 10. DISTRIBUTED ANTENNA ...............................................................................................................46
FIGURE 11. DISTRIBUTED BTS .......................................................................................................................47
FIGURE 12. ALTERNATIVE DEPLOYMENT WITH PICO-BTSS ............................................................................49
FIGURE 13. PROTOCOL ARCHITECTURE OF IEEE 802.11 ................................................................................53
FIGURE 14. MAIN OPERATION PROCEDURES OF THE IEEE 802.11 MAC PROTOCOL .......................................53
FIGURE 15. SCATTER AD-HOC NETWORK OF BLUETOOTH...............................................................................55
FIGURE 16. HOME NETWORKING BASED ON HOMERF ....................................................................................56
FIGURE 17. THE FRAME STRUCTURE OF SWAP ..............................................................................................57
FIGURE 18. THE FRAME STRUCTURE OF HIPERLAN/2 ....................................................................................59
FIGURE 19. WLAN MARKET SHARE OF DIFFERENT SEGMENTS .......................................................................73
FIGURE 20. INTEROPERATION BETWEEN WLAN AND 3G ...............................................................................76
FIGURE 21. INTER-SYSTEM MOVEMENT BETWEEN WLAN AND 3G ................................................................76
FIGURE 22. AD-HOC WLAN ..........................................................................................................................78
FIGURE 23. CLIENT-SERVER BASED WLAN ...................................................................................................79
FIGURE 24. WPBX INTER-OPERATION WITH 3G SYSTEMS..............................................................................93
FIGURE 25. LINK WIRELESS TELEPHONE SYSTEM ARCHITECTURE...................................................................96
FIGURE 26. NETLINK WIRELESS TELEPHONE SYSTEM ARCHITECTURE ............................................................98
FIGURE 27. A WIRELESS PBX SYSTEM FOR SMALL SIZE CORPORATE ............................................................121
FIGURE 28. WLAN 11MBPS SYSTEM ARCHITECTURE ..................................................................................122
FIGURE 29. UNIFIED 3G WIRELESS NETWORK ..............................................................................................123
FIGURE 30. VPN (IPSEC) PROVIDES WIRELESS NETWORK SECURITY ............................................................125
FIGURE 31. HIPERLAN/2 USED IN A CORPORATE NETWORK .........................................................................126
5
LIST OF TABLES
TABLE I. BANDWIDTH AND RANGE OF REPEATER FROM DIFFERENT SUPPLIERS ..............................................17
TABLE II. COMPARISON OF PRODUCTS OF MAJOR SUPPLIERS ..........................................................................19
TABLE III. CAPITAL COST OF ITEMS IN BASE STATIONS AND REPEATERS........................................................31
TABLE IV. COMPARISON OF CDMA PICO-BTS PRODUCTS ............................................................................34
TABLE V. FREQUENCY BANDS FOR GSM BASE STATION SYSTEMS .................................................................35
TABLE VI. PICO-BTS POWER CLASSES ...........................................................................................................36
TABLE VII. COMPARISON BETWEEN 802.11 AND HIPERLAN/2......................................................................60
TABLE VIII. DIFFERENT PHYSICAL LAYERS SPECIFIED BY IEEE 802.11 ........................................................63
TABLE IX. COMPARISON OF ACCESS POINT PRODUCTS OF MAJOR SUPPLIERS .................................................68
TABLE X. COMPARISON OF LAN ADAPTER PRODUCTS OF MAJOR SUPPLIERS .................................................68
TABLE XI. COMPARISON OF LAN BRIDGE PRODUCTS OF MAJOR SUPPLIERS...................................................69
TABLE XII. SYSTEM PARAMETERS .................................................................................................................70
TABLE XIII. RANGES POSSIBLE FOR DIFFERENT DATA RATES .........................................................................78
TABLE XIV. PRICE COMPARISON OF DIFFERENT COMPONENTS OF WLAN PROVIDED BY MAJOR SUPPLIERS ..85
TABLE XV. SYSTEM CAPACITY AND AREA COVERAGE ...................................................................................96
TABLE XVI. COST COMPARISON OF WLAN AND WPBX (UNIT: $) ..............................................................109
TABLE XVII. COMPARISON OF THE FEATURES AND SERVICES OF PICO-BTS AND WLAN ............................112
TABLE XVIII. COMPARISON OF THE COSTS OF PICO-BTS, WLAN, AND WPBX ..........................................115
TABLE XIX. COMPARISON OF THE MARKETS OF PICO-BTS, WLAN, AND WPBX .......................................116
6
Introduction
Wireless technology is the solution to fulfill people’s desire to communicate from
anywhere and at anytime. In order to succeed in the fierce competition of the wireless
market, it is imperative for a company like KTICOM to adapt the recent most
technologies in this area.
In this report, we have given detailed description about various alternative
wireless technologies for KTICOM to keep its leading position in the future competitive
wireless market. We introduce, analyze and compare each technology with respect to its
technical advantages, forecasted markets, costs, and service capabilities.
In Chapter 1, we talk about Wireless Repeaters. Repeater is a bi-directional RF
amplifier used to extend the reach of a base station. The standards and present use of
Wireless Repeater are discussed in first section. Then, different types of wireless
repeaters, market forecast, service analysis, network design, deployment scenarios, and
network cost analysis are given detailed discussion in later sections.
Pico-BTS technology is investigated in Chapter 2. Pico-cellular solutions can
offer higher capacity and better service quality inside buildings. Pico-cell base station
systems are also suitable for shadowed areas and over-populated subscriber regions.
Section 1 and 2 discuss about technology and standards of Pico-BTS, followed by
characteristics, advantages of different types of Pico-BTS. The subsequent sections
present a detailed analysis of environmental effect, safety, expected market, network
design and deployment of this technology.
Great details about Wireless LAN technologies are provided in Chapter 3. We
start with an overview of various standards and types of Wireless LAN. Products from
major suppliers are compared from different prospective. The issue of
internetworking/integration of WLAN with IMT-2000 is presented too. The last few
sections focus on various network deployments scenarios, network security plans and
network cost analysis.
Chapter 4 is about Wireless PBX technology. A Private Automatic Branch
eXchange (PABX or PBX) is a private telephone system within an enterprise that
switches calls between the enterprise users on local lines automatically. Technology
analysis, products from different vendors, main target market deduction, technology
development prospect, internetworking with IMT-2000 and network design issues are all
presented here.
Chapter 5 gives a detailed comparison of Wireless Repeater and Pico-BTS.
WLAN and WPBX are compared in Chapter 6. Then, Chapter 7 compares Pico-BTS and
WLAN/WPBX.
Chapter 9 presents different alternatives using the technologies mentioned above
for in-building network design and deployment, followed by the final Conclusion.
7
1.
Wireless Repeater
1.1.
Overview
In a wireless communication system, a repeater consists of a radio receiver, an amplifier,
a transmitter, an isolator, and two antennas [1]. The transmitter produces a signal on a
frequency that differs from the received signal. This so-called frequency offset is
necessary to prevent the strong transmitted signal from disabling the receiver. The
isolator provides additional protection in this respect. A repeater, when strategically
located on top of a high building or a mountain, can greatly enhance the performance of a
wireless network by allowing communications over distances much greater than would
be possible without it.
Traditionally, repeaters have simply been bi-directional RF amplifiers used to
extend the reach of rural base stations, or to allow in-town base stations to cover areas
shadowed by hills, valleys or buildings. Currently, a repeater is no longer just antennas,
amplifiers and connecting cables [2]. The technology between the base station
communication end of the system and the remote transmitters/receivers has evolved to a
new, more capable level. For example, fiber optic inter-connection and adaptive
interference cancellation (AIC) could be two additional features of wireless repeaters [2],
[3], [4], [5]. The low loss characteristics of fiber allow a carrier to centralize base station
radios and distribute radio signals to desired coverage areas where the size or cost of
deploying additional base stations is not feasible. These repeaters are designed to enhance
coverage and capacity in airports, malls, offices, campuses, industrial facilities, dense
metropolitan areas, tunnels and highways. With the advantages of AIC, repeaters can
have higher power, because AIC achieves much greater input/output isolation by
canceling out the repeaters' own transmissions. Self-interference, which formerly limited
the power and range of a repeater, is reduced by 30 dB or more [2].
Various standards, e.g., [6], [7], [8], [9], have been proposed for wireless
repeaters in different application environments such as GSM, 3G systems, and wireless
local area networks (WLAN). The objective of these standards is to make wireless
repeaters fully compatible with CDMA, TDMA/IS-136 and PCS1900/GSM, and also
forward-compatible with 3G/cdmaOne and W-CDMA.
Compared to base stations, wireless repeaters have many advantages:

Extended transmission distance and increased coverage of wireless networks. This is
the basic function of repeaters. By using wireless repeaters, the wireless signal can
reach a longer distance. Some places such as hilly and shadowed areas, tunnel, inbuilding areas, and mine fields can be easily covered by repeaters.

Reduced initial cost of wireless networks. Using repeaters instead of base stations can
greatly reduce the cost. In some areas such as tunnel, shadowed areas, and highways,
it is not necessary to deploy base stations because the overall traffic is not very high.
Using repeaters, the backhaul traffic can also be more concentrated so that less
backhaul links such as T1/E1 are needed [4].
8

Easy deployment. Since repeaters are much simpler than base stations, they can be
deployed easily and can be mounted anywhere. Moreover, when repeaters mounted
on top of a tower, which is infeasible for base stations, can greatly improve the link
budget [3].

Improved capacity of existing wireless networks. Besides extending the coverage,
repeaters can also improve capacity of wireless networks [2]. This feature is not
obvious since no more base stations are added to the system. However, repeaters
allow each base station to operate closer to its capacity by filling the "blind spots" in
the coverage. By eliminating unusable capacity, more locations are served by the
same number of base stations.
Some issues exist in wireless repeaters. One typical problem is the interference.
For example, other radio communication devices in the same area can degrade the
performance of wireless repeaters. Thus, certain rules must be used to provide reasonable
protection against interference. Another typical issue is that harmful radiation of wireless
repeaters must be avoided since repeaters are much closer to human beings in order to
extend the coverage of base stations. Again, regulations of operating radio devices must
be followed when manufacturing and using wireless repeaters. Moreover, deploying
many towers and equipment of wireless repeaters around residential and in-building areas
cannot always get user acceptance.
However, due to their advantages, wireless repeaters are being widely deployed.
Companies such as Repeater Technologies have achieved great experience in developing
and deploying wireless repeaters. Considering the quick evolution of wireless networks,
new technologies still need to be developed in order to satisfy future requirements of
wireless networks. First of all, the existing issues of wireless repeaters need to be
resolved. Moreover, support of high speed and multimedia traffic is one of the
challenging demands on future wireless repeaters. Also, a future wireless repeater must
have the capability of being both backward-compatible with 2G and 3G wireless systems
and forward-compatible with next generation wireless systems.
Wireless repeater is one of the key technologies for wireless communications.
They will continue to be important components of wireless networks.
In this report, we give a comprehensive investigation of wireless repeater
technologies. In Section 1.2, we first describe the functions, techniques, and standards of
wireless repeaters. Then, current applications of repeaters, interference, and
environmental issues are investigated. In the final part of this section, major suppliers of
wireless repeaters are presented. In Section 1.3, repeater types are categorized.
Characteristics of different types of repeaters are also addressed in this section. The target
market forecast and technology development prospect are reported in Sections 1.4 and
1.5, respectively. Services provided by repeater technologies are presented in Section 1.6.
Network design plan and network deployment technology based on wireless repeaters are
analyzed in Sections 1.7 and 1.8, respectively. In Sections 1.9 and 1.10, the network
deployment scenarios and cost analysis are presented.
9
1.2.
1.2.1.
Technology, Standardization, Present Conditions of
Repeaters
The Repeater Technology and Standards
When the target receiver is beyond the range of the wireless transmitter, and is therefore
incapable to receive transmissions directly, we need repeater links. On the other hand,
deployment of repeaters can allow bases stations to support traffic in high usage areas,
thus achieving a flexible capacity.
A repeater is a network device that repeats a signal from one port onto the other
ports to which it is connected. Repeaters are low-level devices that amplify or regenerate
weak signals, i.e., it merely passes along bits of data, even if a data frame is corrupt. A
repeater does not filter or interpret anything; instead, it merely repeats a signal, passing
all network traffic in all directions.
Wireless repeater, or wireless relay station, can extend the coverage/range of a
base station, without the need to install additional wired base stations. It does not need an
Ethernet connection. In instead, as shown in Figure 1, wireless repeater establishes a
wireless communication link to one or more access points that are connected to an
Ethernet LAN, while concurrently supporting wireless communications with stations
within its local coverage area.
10
Figure 1. Wireless Repeater
A wireless repeater consists of a radio receiver, an amplifier, a transmitter, an
isolator, and two antennas. Each repeater has a transmitting and receiving range of
between 100 to 1500 feet (30 to 450 m) depending on different terrains and different
manufactures. We call such range as Line of Sight.
Typically, there are three different cases to use repeater:

Single Repeater. This is the simplest way to use a single wireless repeater to extend
the radio coverage.

Multiple transmitter networks. In this case, we set one repeater to listen to up to a
number (example: 8) transmitters directly, and then re-transmit those signals to their
respective receivers, as shown in Figure 2.
11
Figure 2. Multiple transmitter networks

Multi repeater networks. In case of the distance between the transmitter and the target
receiver is too large to be covered with a single repeater, we should use several
auxiliary repeaters together along the communication path. Each auxiliary repeater
retransmits data received from another repeater. Another condition is to improve
signal reception in hilly, heavily-wooded or urban areas. In this way, we create a
multiple repeaters network, as shown in Figure 2.
A Repeater Network extends range in layers and such layers may overlap. However,
we cannot go beyond 4 layers of range. Another fact is that data travels along a single
path to the receiving transceiver.
The network is self-configuring, i.e., it periodically discovers the devices to which
they can connect. It is also self-correcting: when one path between the transceiver and
a remote target is unavailable, the network will choose another path automatically.
Figure 3. Multiple repeater networks
Depending on the working area, different standards should be applied to wireless
repeaters [8]. In a wireless LAN environment, IEEE 802.11 wireless LAN is a typical
standard. In such a standard, an access point is specified. It can be switched into repeater
state depending on the necessity. Thus, the functions and requirements of wireless LAN
repeaters are implicitly specified in IEEE 802.11. In larger wireless environment such as
fixed wireless communication areas, IEEE 802.16 standard draft specifies an optional
12
configuration for IEEE 802.16 networks. In one of the three interface specifications of
IEEE 802.16 [10], a wireless repeater is used to bypass obstacles and extend cell
coverage.
For wireless cellular systems, many standards are available for repeaters. These
standards can be categorized according to the evolving phase of the wireless cellular
networks. For example, for GSM network Release 1999, the standard is GSM 11.26
v.8.0.2 [1]. In each release of GSM network, there is a standard for repeater. Although
there are some differences between these releases, most of the contents are similar. In the
3G networks such as UMTS, repeaters are specified in standards 3GPP TR 25.106 v.4.0.0
[7] and 3GPP 25.956 v.4.0.0 [8]. Similarly, both standards have multiple releases.
1.2.2.
Current Use of Repeaters and Industry Practices
Repeater technology offers operators a chance to optimize network capacity and
coverage, cut operating costs, speed up network roll-out, and reduce capital expenditure.
Traditionally, repeaters have been used to improve RF coverage so as to improve voice
quality and reduce the dropped call rate. However, the largest benefit is the reduction in
cost per coverage area. Repeaters are small and light which makes site acquisition easier
and less expensive. Operators' licensed spectrum for repeaters eliminates the need for
microwave links and other transmission equipment. The following are the typical areas
where wireless repeaters are extensively used:

Problematic environments. In problematic environments, there is often a pressing
need for reliable radio coverage. Wireless repeaters can be used to solve the problem
in these environments without increasing too much cost.

Highways and small villages. The coverage of highways and small villages along the
road is an important task but often associated with very high initial costs. Wireless
repeaters present a cost-effective solution to this problem. For example, when using
frequency-shifting repeaters in combination with base stations to cover highways,
roll-out cost savings can be up to 40% [11].

Coverage gaps. It is annoying that customers' calls are dropped because of coverage
holes in the mobile network. Coverage has become an important competitive issue for
the operators. However, covering a limited area with a complete new base station is
often unnecessarily expensive. In such situations, a repeater is a cost effective
alternative.

In-building areas. For in-building coverage, using repeater is essential in many old
buildings. Installation costs, generally the most expensive part of an in-building
coverage project, can be kept to a minimum when using repeaters. Also, deploying
base stations inside a building is not always practical.
Currently, many companies are manufacturing wireless repeaters. Their practices
have shown the benefits of using repeaters:

Repeater Technologies. This company proposed a repeater hybrid network (RHN) for
CDMA carriers [3]. To date, more than a dozen CDMA carriers have designed or
turned up networks that are utilizing RHN architecture. Compared to all base station
approach, an RHN can save up to 30--60% cost in low traffic areas. Several key
13
technologies have driven the promising development of repeaters in this company.
First, the repeaters are taken to new heights. The towers can be as high as 300 feet,
and repeaters are mounted on top of towers. In such a way, 3 dB link budget can be
gained, which translates into additional 30% of coverage [3]. Second, high
performance donor antenna is used to pick up the base station donor signals from
farther distances without isolation problems. Such a high performance donor antenna
is achieved by suppressing E field, increasing antenna gain, and using narrow beamwidth. There are two configurations of RHN: cascaded and parallel [5]. In cascaded
configuration, the base station signal is passed down the line from repeater to
repeater, up to a maximum of two repeaters in a given chain. A cascaded repeater will
project 75% of its power forward down the chain and 25% of it back through a backbeam antenna that fills in the weaker, fading portion of the donor signal. Cascaded
repeaters are particularly useful for covering hilly and curvy terrain where line of
sight (LOS) is difficult. In parallel configuration, towers are placed further from the
BTS and are equipped with two repeaters --- along with a larger, more sensitive
receiving antenna to receive more distant BTS signal. One repeater transceives back
toward the BTS, the other away from it --- both at 100% power. The parallel setup is
ideal for straighter, flatter terrain. It also provides a greater degree of network
reliability because only one segment will lose coverage in the event of an equipment
failure. The repeaters from this company have been applied to different environments
such as huge mall, highways, world cup skiing field, mountain areas, low population
density but large coverage areas like Australia [3].

Allgon Inc. Allgon's repeater system equipment provides cost-effective solutions for
creating clear and reliable signal coverage, with minimal dropped call rates, in all of
the traditional problem areas of cellular mobile systems, such as tunnels, shopping
centers or mountain valleys. Simply by extending the coverage of base stations, they
reduce infrastructure costs as well as improving a system's overall trunking efficiency
by reducing the number of base stations that need to be backhauled to the switch.

Avitec Inc. Avitec designs and manufacturers repeaters for both mobile telephone and
trunk radio networks. Repeaters provide new and experienced network operators with
choices. Increasing the network coverage can be achieved with varying combinations
of both base stations and strategically placed repeaters. The alternatives in expansion
methods allow the network operator flexibility in reducing the overall cost.

DECT Repeater Manufactures. The technology of DECT repeaters is reasonably
straightforward but sales volumes are small compared to the mass markets for
cordless telephones. Thus, at the start of 1999, these products are primarily being
supplied by small players rather than by the major players.
o Dancall. Cordless repeater equipped with a special directional aerial. The
repeater relays signals between the handset and the base station and can
double the range of the system.
o Kirk Telecom. Kirk Telecom is one of the few manufacturers to be
actively promoting a range extender product. The repeater is generic
access profile (GAP) compliant and thus can be used with any
manufacturers' DECT GAP telephones. The product is specifically
14
applicable to use in a business multicell environment, where it can provide
improved coverage in black spots as well as flexing traffic capacity in high
usage hot spots.
o RTX Telecom. Early products from this company followed the ETSI
wireless relay station specification ETS 300, 700, GAP (TBR22), and
CTR6, and thus, were suitable for operation with a range of manufacturers'
DECT phones. The newer product features an exclusive design that fits
into almost all DECT product programs, yet is small enough in size to be
able to integrate discretely into any user environment. It includes a built-in
directional antenna and improved range and contains clever software that
allows plug-and-play installation for the end user, using a new matchless
automatic registration method. With this feature, the repeater
automatically assigns itself to the most powerful DECT GAP base station.
For the end user this means that the repeater installation has been reduced
to plug-and-play.
o Smart Telecom Solutions. Digital personal repeater (DPR) in this company
is available as a module. The DPR is suitable for low data rate point-topoint connections. By implementing the GAP protocol, the DPR can
operate with existing DECT installations, using the existing DECT
infrastructure.

QUALCOMM and Ortel. QUALCOMM and Ortel Corporation worked together to
develop and optimize the required technology for a receiver diversity option in
CDMA repeaters. They successfully demonstrated measurable performance
improvements through the use of diversity. On the one hand, repeaters are a proven,
cost-effective technology for enhancing coverage and expanding cell site footprints in
CDMA networks. On the other hand, the use of receive diversity in a CDMA repeater
has been shown to reduce mobile transmitter power and signal to interference ratio
(SIR), resulting in an increased range for the repeater and cell site, improved battery
life for the mobile, and improved capacity for the cell site associated with the
repeater. CDMA operators have experienced the benefits of using repeaters as
strategic network elements to serve cover difficult coverage areas and expand rollout. Ortel's wireless repeater product has been proven to provide both indoor and
outdoor coverage in commercial CDMA networks, reduce infrastructure cost, and
expedites roll-out of wireless networks.
15
Manufactures
Network
Featured
Techniques
Coverage
Repeater
Technologies
[20]
AMPS/TDMA
/CDMA
Avitec
[101 ]
Allgon
[102]
GSM mobile
phone
and
trunk
radio
networks
High tower and Fiber
optic
high
distributed
performance
repeater
donor antenna
Qualcomm/Ortel
[103]
GSM, AMPS, CDMA
TDMA,
WCDMA
Channel/band
Receiver
/segment
diversity
selective
repeaters, 3-G
repeaters,
minimized
dropped-call
rates.
60% additional Connected to 78% extension NA
coverage
up
to
2~4 of coverage.
extension from carriers.
a BS.
In the future, capacity of a wireless repeater will become higher and higher in
order to satisfy the multimedia and high speed applications. Due to the increased data
capacity, several problems will arise and need to have solutions.
1. New digital signal processing (DSP) techniques. A certain Signal-to-interference
ratio (SIR) is required for a certain data throughput in a repeater. When the
throughput is higher, the SIR needs to be increased. In order to achieve a good
SIR, new DSP schemes need to be proposed.
2. New antenna and diversity techniques. In order to increase SIR, antenna and
diversity can also be used to achieve such an objective.
3. Optical repeaters. Optical transmission in a wireless repeater cannot only achieve
high SIR, but also delivers high speed traffic rate.
4. New network design. With the same type of repeaters, different type of netwotk
design could result in different network performance. The network design needs
to answer the following questions:
a) what kind of architectures must be used: cascaded or parallel, or hybrid?
b) How to connect repeaters to base stations?
c) How to optimize the number of repeaters?
5. New management tools. In order to optimize the network configuration and
performance of high speed wireless repeaters, management tools need to be
developed. The tools should have easy-to-use interface to network operators.
1.2.3.
Detailed System Analysis of the Repeater Technology
The function of a repeater is to increase the signal strength/power. Conceptually, it can be
viewed as a simple amplifier which amplifies the received signal and then retransmit the
16
amplified signal. The transmitted signal frequency differs from that of the received one.
This frequency offset is necessary to prevent the strong transmitter signal from disabling
the received signal.
To accomplish its function, a repeater consists of a radio receiver, an amplifier, a
transmitter, an isolator, and two antennas (one for reception and another for
transmission). The radio receiver receives the incoming signal, the amplifier amplifies the
received signal and the transmitter transmits the amplified signal. The isolator isolates the
low-power received signal and the high-power transmitted signal from each other, hence
gives protection to the received signal from the transmitted one. The receiving and
transmitting antennas are either directional or omni-directional depending on application
and network configuration. When the network is such that the repeater is designed to
amplify the signal coming from only one direction and then transmit that in another
direction, the antennas used are directional. On the other hand, when the repeater is
designed to receive and send signal in all directions the antennas are omni-directional. It
can also be possible that one antenna (either receiving or the transmitting) is directional
and the other one is omni-directional, depending on the application scenario.
Repeater can be AC powered, solar powered, battery powered, partly solar and
partly battery powered etc. The power supply mode depends on its use to a great extent.
For example, when a repeater is used in WLAN network usually it is battery powered.
One used for recording weather condition is usually solar powered along with a battery
which gets charged during day time to be the power source during night. When the
position of a repeater is fixed (as in case of a repeater used to cover the shadowed regions
of cellular network), usually it is AC powered.
Repeater Technology use lower frequency band, in most cases the ISM band (in
US prospective bandwidth of 26MHz, 83.5 MHz and 125MHz around 915MHz, 2.4GHz
and 5.8GHz respectively). Hence FCC license (in US prospective) is not required.
Typical frequencies used by repeater from leading Wireless repeater providers are in the
in the range: 300MHz- 6 GHz.
Table I gives information about the bandwidth and range of repeater from
suppliers: (a detailed description of repeater products is provided in Section 1.2.6).
Table I. Bandwidth and range of repeater from different suppliers
Supplier
The solutions Group
Allen Telecom
1.2.4.
Typical bandwidth (MHz)
10
5-18
Range (m)
8000
54
Interference to Repeaters
When a repeater is in operation, interference is an important factor that needs to be
considered. For example, a 2.4 GHz repeater in can be virtually unusable because of the
very high noise caused by Part 15 license-free devices [12].
17
The interference to repeaters mainly comes from two sources:

Equipment working in the same frequency band. Although certain rules on
interference are supposed to be followed if devices work in the same frequency band,
interference still exist due to open air of wireless links.

Repeaters working in the same system. In such a scenario, multiple repeaters are in
the same system. Since these repeaters work in the same frequency band, one repeater
experiences interference from other repeaters.
In order to reduce interference experienced by a repeater, several ways can be
used:

When a repeater works in a license-free band, it must experience interference from
different devices working in the same frequency band. One way to reduce interference
is to make the surrounding environments of the repeater be clear enough so that the
interference level is not so high. The other way is to use DSP techniques in the
repeater so that interference can be suppressed.

If a repeater works in a licensed band, its experienced interference must be low. In
the case that other devices generate interference at an unacceptable level to the
repeater, these devices need to be removed, changed, or modified. In such a situation,
DSP techniques used in repeaters also help to reduce interference.

Since repeaters of the same system may interference with each other, the deployment
of repeaters is very important in order to reduce interference. The neighboring
repeaters can be cond so that they are working in a different time duration, such as the
parallel configuration of repeaters in Repeaters Technologies. The repeaters also need
to be deployed with enough distance in-between of them. Moreover, the transmitting
power and antenna sensitivity are also parameters that can be used to reduce
interference.
1.2.5.
Environmental Issues
Compared to base stations, repeaters have some advantages in terms of environmental
issues. For example, it is more acceptable to deploy repeaters inside a building because
repeaters have simpler architecture, low cost, smaller effect to human health. However,
because repeaters are more likely to be deployed to the environments that are close to
human beings, its effects to human beings need to be paid attention to:

Radiation of magnetic waves. It is proved that electro-magnetic waves have harmful
effects on human health. There are several national and international safety guidelines
for exposure of the public to the RF radiation produced by the antennas of any device,
and hence for repeaters. The most widely used standards are those developed by the
ANSI/IEEE and the International Commission on Non-Ionizing Radiation Protection
(ICNIRP), and the National Council on Radiation Protection and Measurements
(NCRP).These standard bodies have defined their guidelines both with respect to
frequency of radiation and its power level. For wireless repeaters, even though
different companies have different frequency of operation which varies from around
300MHz up to around 6GHz, still this is much below the one specified by the above
standard. Hence, repeater technology does not pose as a threat to the user and people
18
around. Thus, all the suppliers of repeaters should strictly follow the above safety
requirements with quite a reasonable margin. In such a way repeaters are safe to use.

Appearance of repeaters. When many repeaters are deployed in a building, along
streets and highways, and on a scenery mountain, it is generally not acceptable that
many towers are there just for deploying repeaters. Thus, some repeaters vendors
manufacture some tree-like towers for repeaters along street and highways. Inside a
building, the repeaters are built into a smaller size and can be attached on the ceiling
or wall so that repeaters are relatively far from the crowd. Since normally a building
has been wired with cables, thus wiring between repeaters and BTS are not a
significant issue of user acceptance.
1.2.6.
Major Suppliers of the Repeater Products
As the market for repeater is growing, the number of products is also increasing.
Different products are suitable for different applications, hence have different range,
bandwidth, power consumption. Table II gives a brief comparison of repeaters from
different suppliers.
Table II. Comparison of products of major suppliers
Major
Suppliers
Davis
Visonic
Cylux
Technologies
Repeater
Technologies
Allen
telecom
Freq of
operation
(MHz)
916.5,
868.35
315, 404,
433.9
1860-1870
| Bandwidth
(MHz)
LOS range
(m)
Power
supply
--
122
AC, Solar
Power
consumption
(W)
0.5
--
300
AC, DC
0.3
9.4
--
AC
--
870-880
12.5
--
AC,DC
--
824-849
5-18
54
AC
--
The repeater of Repeater Technologies is designed for long range, and also has
high output power/carrier. Hence its power consumption is much higher compared to
others.
1.3.
Repeater Types and Their Characteristics
There exist various ways to classify Repeater types. One such way is according to the
Technology/Frequency used. The major types of repeaters now being used for extension
of cellular network coverage to blind spots, are:

Fiber-Optic Repeater: Fiber-Optic repeater receives, amplifies, and then retransmits
signals over the fiber cable between the base station and remote antenna. It addresses
the need to extend the mobile cellular network to locations that were previously blind
19
spots. Fiber-Optics technique is selected as one of the solutions because of flexibility
in cable laying design, lower cost of installation, broader service area. The fiber
network is extended from the outside cellular network to the blind spots through
repeaters, which takes care of signal distortion, interference , and propagation loss.
There exists various products from different vendors, some of them are ORS800/1800 Optical Repeater System (operating frequency 800 MHz (CDMA), 1800/1900
MHZ (CDMA PCS) ), DRAN (Digital Radio Access Network) Optical Repeaters
designed for W-CDMA from Airvana, Mikon’s MOR701B Power Remote which
functions as band selective or channel selective optical repeater for GSM, CDMA, and
TDMA.

RF Repeater: RF repeater is a band selective repeater which amplifies signals
between mobile stations and a base station. It is employed to extend the cellular
network coverage to blind spots. These repeaters are nowadays being widely used in
all cellular systems. For example MR701B Power from Mikon. This is a band
selective RF repeater for GSM, CDMA and TDMA and a channel selective repeater
for CDMA and TDMA. This repeater amplifies signal in both directions, between
multiple mobiles and a single base station in the PCS 1900 MHz band. MR301B
from the same vendor operates at 900 MHz with similar functionalities.

Microwave Repeater: Microwave repeater first converts the base station signal to
broadband M/W signal, then amplifies and transmits it to a remote point. Upon
reception the signal is converted back to RF signal and then transmitted via antenna.
There are products from different vendors: MMC CDMA cellular/PCS microwave
repeater from C&S Microwave, MRS-800/1800 CDMA Cellular/PCS frequency band
repeater (operating frequency of 800 MHz (CDMA), 1800/1900 MHz ( CDMA PCS),
with microwave module operating at 18GHz).

Frequency Shift Repeater: Frequency shift repeater consists of a donor unit located
near BTS and a remote unit located in shadow area. These two units are linked by
converted frequency, which is operators non-used band. They are used for extension
of network to outdoors shadow area such as highways, resorts, valleys, road-cuts etc.
Examples of few products: FRS-B (CDMA frequency shift repeater), MGFS-900 of
Mobilink.
There are two main types of repeater systems in use according to public/private
operations:

UHF CB or public frequency repeaters. UFH (ultra high frequency) is the region of
the radio spectrum between 300 and 1000 MHz.

Private Repeaters for commercial operations.
20
According to repeater's functionalities, there are following types of repeaters:

Over-the-air repeater (off-air repeater). It is the most common type of repeater.
Over-the-air repeaters use a frequency translation scheme. It operates entirely on one
pair of frequencies which are used by the donor BTS. While working similar to a
mobile terminal and repeating the signal at the same frequency into the desired
coverage, Over-the-Air Network Repeaters offer the lowest cost alternative. Many
manufacturers provide over-the-air repeaters for AMPS, TDMA and CDMA
networks.

RepeaterHybrid network repeater (RHN). RHNs were first introduced by Repeater
Technologies in 1997 for CDMA networks. They can be implemented in noncontiguous suburban, rural and rural highways where RF coverage is the primary
consideration other than capacity. If base stations and repeaters are combined to use,
the base station count can be dropped greatly compared to traditional all base station
deployment.

Hole fill-in repeater. Tunnels, large buildings and hilly terrain often result in wireless
coverage gaps. In this case, the system has already had the required capacity installed.
Then repeaters can be used to fill-in the gaps and thus will save a lot compared to use
base station.

In-building repeater. In some situations, it will be very expensive to install a
dedicated radio base station when for in-building service such as sports arenas,
convention centers, transportation terminals and office buildings. So we use Inbuilding repeater to achieve the same purpose with a minimal cost while having a
high reliability is high.

Linked repeater. Sometimes, we can not use the Over-the-Air Network Repeaters
because of interference limitations. Linked repeaters can provide us an alternative to
bypass such limitations. Since linked repeaters are linked to the donor base station via
a fiber optic cable, they can be utilized in virtually any environment and extend the
same benefits as Over-the-Air Network Repeaters. However, relevant products are
not available for all frequency bands.
ETSI have standards for two types of DECT repeater:

The REP - Repeater Part. It requires a change in the frame structure in the base
station. It results in minimum audio delay but degrades overall system capacity.

The CRFP - Cordless Radio Fixed Part. With this implementation the frame structure
in the handset and base station remain unchanged. It results in additional audio delay
and requires special handling of encryption, but has good system traffic capacity.
1.4.
Main Target Market Forecast
The future of the wireless repeater market is forecast to be huge and its utility is going to
be widespread starting from small and individual domain to large and public domain.
21
1.4.1.
Current Market Segments and Their Penetration
At present the repeater market consists of segments some of which are the existing since
long time for example:

Ham-radio network

Cable-TV network

Fiber optics network

Telephone network (PSTN)
Apart from the above listed traditional uses, repeater technology has captured
several new market segments in last few years, these segments are (to name a few):

Improvement of signal power inside a car in a cellular environment

Coverage of shadowed regions in cellular environment. There are often gaps in
wireless coverage due to shadowed areas from the base station caused by hilly terrain,
large buildings and tunnels. Since the required capacity is already installed, repeaters
become the ideal solution to fill-in the gap because a repeater will cost 75network
setup in mines.

Transfer of weather information from the location under study to the weather
Laboratory
1.4.2.
A Forecast of the Target Markets and Estimated Market Size
Even though the present use of repeaters is not wide spread, this technology is foreseen to
be widely used. Considering its advantages market experts have envisioned a big success
for this technology in the near future. Repeater technology is targeting the following
market segments in the near future:

Setting up Wireless home

Setting up WLAN for offices, shopping malls, educational institutes, factories, mines

Quick network deployment in a area affected by natural calamities like earthquake,
flood, cyclone etc
Out of all the different types of uses give listed above, the second one seems to be
the most promising (considering revenue and wide use). This is expected to have wide
acceptance because of following advantages:

Quick network setup. As infrastructure requirement is much less in case of WLAN
using repeaters, the network setup time of this type of network is much less compared
to the one using base-stations, where the infrastructure requirement is much more.

Low cost. WLAN using repeaters network involve low cost compared to base station
based WLAN environment.

Convenience in network setup. It is very convenient to set up a WLAN using
repeaters compared to the one using only base stations (it is not easy or convenient to
put base stations inside building or factory).
22

Ease of relocation. Relocation of a repeater network is easy compared to other types
of networks.
It has been envisioned that, the existing niche market for second generation
mobile telecommunication repeaters will continue to exist, as existing second generation
mobile telecommunications will continue to spread into remote, mountainous and
secluded regions. Repeater Technology is also going to get more attention and wide
spread use in the upcoming third generation communication technologies. The market for
Repeaters is estimated to be around 100 billion dollars by 2003 [22], [23].
1.5.
Technology Development Prospect Analysis
As wireless communication networking evolves quickly, the repeater techniques also
need to be updated to catch up the pace of the evolution of wireless networks. Generally,
it is expected that the repeater technology will have the following advances:

Repeaters will support high speed of multimedia traffic. In the next generation
networks, traffic will be in a multimedia format. Moreover, in the local area
networks, the applications of end users need more and more bandwidth to transmit
high speed traffic. Thus, repeaters in the future must support high speed multimedia
traffic rate, which in turn requires advanced techniques in antennas, modulation
schemes, and DSP algorithms.

Capacity of a repeater will be increased. As the capacity of a base station will be
greatly increased in the next generation wireless networks, the capacity of a repeater
also needs to be significantly increased. As an example, repeaters of IEEE 802.11 are
able to support traffic rate of 11 Mbps. This number is going to be significantly
increased by advanced techniques in the physical layer of repeaters. For example,
wideband CDMA and OFDM techniques will enhance the capacity of repeaters as
that used in 3G wireless communications systems and wireless networks.

The size, weight, and transmitting power of a repeater will be decreased. In the
future, more repeaters are going to be used to extend the coverage of wireless
networks. In order to guarantee user acceptance, the repeaters will have much lower
size and weight. In such a way, repeaters can be easily installed in different places
without much difficulty. The power consumption of a repeater also needs to be low so
that the cost of repeater is low and its effect to human health is reduced. However, it
is obvious that reducing transmitting power of a repeater requires advanced radio and
modulation techniques.

Repeater networks should be self-configuring and self-healing to accommodate
radios being moved, added or deleted from the wireless system. This feature will
enhance the fault-tolerance of repeater networks. Also, the services in such networks
are guaranteed to be seamlessly continuous. This feature requires that additional
functions of both physical layer and higher layers need to be developed.
23
1.6.
Service Analysis
Different service types can be provided by repeater technology. Depending on different
scenarios where repeaters are used, services are also different, which is described as
follows:

Traditional services such as voice and medium rate data service such as those in
GPRS system. When a 2.5G cellular network uses a repeater to extend the coverage of
highways, mountains, tunnels, the services provided by 2.5G have to be supported by
the repeater.

Multimedia services such as those in 3G wireless communication systems. In the 3G
system, multimedia traffic is supported. In such a system, the repeater must be able to
deliver different traffic types. Basically, the repeater does not need to differentiate the
traffic types, and it just receives and retransmits signals to the destination. However,
because of the more complicated resource allocation at the base station when
multimedia traffic exists, the synchronization of receiving and transmitting signals
between repeaters and base stations must be a very important and difficult issue.
Moreover, the SINR's (???) of signal of different traffic types need to be controlled so
that the BER is satisfied and power allocation is optimized.

Broadcast service. In both terrestrial and satellite networks, repeaters can be used to
extend the coverage of broadcast services such as TV, radio, and other applications.

High speed data service. In wireless LAN environments, an access point can be
switched into the repeater mode. Thus, in such a situation, a repeater is able to deliver
high speed date traffic, which could be up to 11 Mbps as in IEEE 802.11b wireless
LAN. As the traffic rate becomes higher and higher, the repeaters in a wireless LAN
will also be able to deliver very high traffic rate.

QoS guarantees. Although repeaters do not have higher layer functions such as
routing and MAC, QoS guarantee also needs to be considered by them. For example,
if the repeater is based on CDMA technique, BER should be satisfied when signals
pass through repeaters and are received by users or base stations.
1.7.
Network Design Plan Analysis
There exist both wired and wireless networks using repeaters. The wired network using
repeaters have existed for long time. The most common example is the use of repeaters in
Cable-TV network. Similarly, Ham-Radio network is the most common and ancient use
of repeaters in wireless scenario.
The following part of this section focus on design of Wireless Network in LAN or
cellular environment. While designing such wireless networks using repeaters, the
possible topology can be one of the following two types:

Use of one central access point and repeaters

Use of optimum combination of base stations and repeaters
24
Both the above options are good and are suitable to different applications. For
example when the number of users in the network is less and also user mobility is
confined to a small region (for example in a wireless home), the first option is good
enough. Whereas, when number of users is more and/or the area of coverage is large, as
in case of wireless factory/wireless office/wireless educational network, network
management load is much more. And use of single base station will make it more
complex and expensive. In such cases it is wise to use an optimum combination of
repeaters and base stations. This type of network is also known RepeaterHybrid
Networks (RHN) [20].
The use of RHN is emerging as a promising solution because of its following
advantages:

Full coverage of cellular environment. It extends the network coverage to the
shadowed region of cellular environment.

Reduction in number of base-stations. The number of base stations is reduced to 50
network setup.

Minimization of network operational cost. The operational cost of the RHN network
is around 50consisting of only base stations.
1.8.
In-Building Network Design Alternatives Using the
Repeater Technology
Repeater technology gives a practical solution to extend the cellular wireless
communication technology to each and every corner of the indoor space e.g. deep corners
of buildings, ramps of parking space, and corners of shopping malls, which usually fall
into shadowed region of the base station antennas. Here the idea is, by using repeaters it
will be possible to establish a connection between the mobile and the base station (even
when the mobile is in shadowed region of the base station), and thereby maintaining the
communication without call drop. Here, repeater functions as an intermediate bridge
between the base station and the mobile.
An in-building network design using repeaters is quite similar to the in-building
cellular network setup with certain differences. To start with the network can consist of
few transceivers (as few as two) [24]. One of these will function as central transceiver
(known Central Access Point, CAP), and the other one will get connected to this using a
wireless link. When more subscribers need to be added to this network one of the
following situation will arise,

The new subscriber is within the LOS of the CAP, or

The new subscriber is outside the LOS of the CAP
25
Figure 4. Wireless network within a single cell
In the first case, (as shown in Figure 4) the new subscriber gets connected to the
network through one wireless link between the new subscriber and the CAP. Here the
network expansion and configuration is exactly the same as that of the cellular network.
In Figure 4, '1' represents the CAP and '2' the initial subscriber. Then subscribers '3' to '8'
are added afterwards. All these subscribers are with in the LOS of CAP.
Figure 5. Wireless Network using repeaters
In the second case, when the new subscriber is outside the LOS of the CAP
(subscriber '9' as shown in Figure 5), a cellular network would require a new base station
26
at the center of a new cell to cover the new subscriber, and a backbone connection
between the two base stations. But in case of network using repeaters, what need to be
done is to find an already existing subscriber which happens to be within the LOS of the
new subscriber (e.g. subscriber '2' as shown in Figure 5). Then a wireless link is set up
between this subscriber and the new subscriber. This already existing subscriber works as
a repeater. The new subscriber gets connected to the CAP through this repeater. A
situation might arise when there is no existing subscriber which is with the LOS of the
new subscriber. In such a case we can set up one or more new repeaters to add the new
subscriber to the network. Here we have seen that just by using repeaters, we get rid of
the new base station requirement in case of a cellular network.
As the network grows, any of the already existing subscribers (also known as
network node) can be promoted to become a repeater by setting a wireless link between
this and the newly added node. Hence, the only requirement for a new node to get
attached is to have a wireless (in most cases RF) link to any one of the already existing
network node. This type of network topology is known as "anypoint-to-multipoint", since
any node already in the network can become the center of a point-to-multipoint branch.
As more and more nodes are deployed, the range and coverage of the network grows.
This way the locations like deep corners in a house, shop, office or ramps in parking lot,
which fall into the shadowed region of cellular environment, can be covered by the
network.
We can keep on increasing the range and capacity of our network in the above
mentioned way so long as, the network load is within the capacity of the CAP. Once the
network load becomes more than the CAP capacity, the need for an additional base
station arises. And the network can be increased around the second base-station, with a
backbone network between two base stations. This is how a RHN, is setup in an indoor
environment.
1.8.1.
Coverage and Capacity Analysis as Part of the Network
Design Process
As we have seen in the above section, once the network grows beyond the LOS of the
(CAP), there arise a need for a repeater. And by using this repeater the coverage of the
network is increased. The coverage radius around each repeater and hence the CAP
depends on the range of the antenna used by the CAP and the repeaters. In present
market, repeaters are available with ranges as small as 50m to that of 8000m. Hence
appropriate repeaters can be used depending upon the network coverage requirement.
Capacity of the network is going to decide how many base stations we need and
this number can be dependent on the type of the base station used for the network design.
If the available base station can handle large network load and has more range, the
network can be designed with fewer base stations. Whereas if the load-handing capacity
of the base station is low and also it's range is small, then more number of base stations
are used to get the same network capacity and coverage.
From the above discussion, it is clear that depending upon network specifications
like required coverage, required capacity, and also type of repeater and base station
available for the network design, the optimum number of repeaters and base stations
27
required for the network design can be calculated. This is very critical to ensure the QoS
for the network users.
1.9.
Network Deployment Technology and Premise Network
Security Plan
In order to implement the most common over-the-air repeater network, we should deploy
with donor antenna technology effectively. First, we should optimize the repeaters and
donor antenna design for satisfactory performance. We also need network management
(operation and maintenance) software for the repeater site elements. These requirements
are especially important to achieve a robust RHN (repeater hybrid networks).
Many companies use repeater technologies combined with satellite
communications to build up their broadcast network. They will create up to 100 channels
with digital-quality. In this way, repeaters network will augment the satellite system by
re-transmitting its signals in dense urban areas where the satellites' signals may be
shadowed by tall buildings and other obstructions. Technology will include the use of
COFDM (Code Orthogonal Frequency Division Multiplex), which is a superior
modulation technique for the delivery of high quality audio, video and data. This
modulation technique allows a moving vehicle to receive quality service at highway
speeds.
To protect network security and to reduce fraud, each receiver will contain a
security circuit with an electronically encoded identification number. Only if the
verification of receiver is correctly passed, the repeater network will transmit a digital
signal to activate the receiver's capability.
1.10.
Network Deployment Scenarios
In a wireless network, repeaters can be deployed in several ways:

Single repeater. In this scenario, one repeater is only used between a transmitter and
one or multiple receivers.

Daisy-chain installation [13]. In this scenario, multiple repeaters are installed in a
succession to extend the distances between a single transmitter and one or more
receivers.

Network Installation [13]. In this scenario, multiple repeater/transmitter ID DIP
switches are in a single repeater, which can be turned ON/OFF depending on
necessity. This scenario can have three possible configurations:
o Single repeater and multiple transmitters and receivers.
o Multiple repeaters and one transmitter and one receiver.
o Multiple repeaters and multiple transmitters and receivers. In this case,
repeaters are deployed in a succession mode. How, each repeater is able to
receive signals from transmitters or transmit signals to receivers.
28
Specifically, the deployment scenarios are different depending on environments.
Typical ones are analyzed as follows:

A building or a cluster of buildings such as a mall. In such a case, normally one base
station is installed on top of a building, repeaters are installed on different places of
the building so that wireless services can be covered at all corners of the building. In
such an environment, all the above-mentioned deployment alternatives can be
applied.

Highways. In order to extend the coverage of wireless services on highways and
reduce the cost, repeaters are deployed like a daisy-chain configurations. Along a
highway, there are multiple repeaters installed in a succession and then connected to a
base station.

Mountains. In a mountain area such as a snow skiing field, normally, a base station is
installed at the lower part of the mountain so that higher traffic rate in this area can be
satisfied. Due to lack of LOS on top of a mountain, a repeater can be used to provide
the coverage of wireless services. This environment belongs to the single repeater
deployment scenario.

Tunnels. In such a scenario, a single repeater can be applied on the ceiling if a tunnel
is not long. When it is very long, multiple repeaters are required. Thus, the daisychain installation is more applicable to this scenario.

Stadium. Because of bursty traffic rate depending on the sport events, using repeaters
in such an environment can greatly reduce the cost of providing good quality of
wireless services. In a stadium, the most appropriate way is that multiple repeaters
together with multiple base stations are deployed according to the network
installation alternative. A repeater can communicate with multiple transmitters and
receivers, multiple transmitters and receivers can communicate with one repeater, or
multiple repeaters communicate with multiple receivers and transmitters.
1.11.
Network cost analysis
Many people know the advantage of repeater cost savings, and regard it a strong
economic motivation to deploy repeater other than base station and microcell. Repeater
cost savings can be achieved via 2 respects: capital saving and operating saving.
If BTS or microcell is replaced with a repeater, lots of capital savings can be
gained. The reduction of relevant hardware and software required by BTS or microcell
will save much cost.
By using wireless repeaters, we do not need E1/T1 backhaul and their
corresponding maintenance time and utility costs. Thus, we gain many operating savings.
We can also save the downstream capital costs associated with BTS or microcell use,
including port cards, per-BTS operating software, maintenance fee, leased fee, and perBTS feature software.
29
There are many cases in which network coverage is the first consideration rather
than network capacity. Users use a repeater-augmented solution to extend the coverage of
each cell with over-the-air repeaters. By this means they can cut costs by up to 45%.
For RHN applications, we combine base stations and repeaters rather than use the
all-base station solution while providing the required coverage. In an RHN
implementation, the base station count can be saved by 50% for suburban/rural, coverage
and by 67% for rural highways compared to the traditional all-base station solution. The
RHN design can extend the BTS's coverage to a greater area.
An example is explained as follows [25]. In a typical suburban area with 1.2
million POPS, the total coverage area would be about 2,600 square km. For 90%
coverage quality, each CDMA PCS cell would be 30.1 square km, requiring 87 cells at
$400,000 each, or $34.8 million. Assuming an aggressive 3% penetration rate and usage
of 0.03 Erlangs/subscriber, this CDMA build out would leave you with 80% wasted
capacity.
If you modified the cells to consist of a base station and three over-the-air
repeaters, you would increase cell coverage to 52.8 square km shown in Figure 6. With
this build out structure, it would only take 50 repeater-augmented cells at $490,000 each,
or just $24.5 million in capital. Your savings would be 30% and your underutilized
capacity would be virtually eliminated. Moreover, you would have 37 fewer cells for
your switch and BSC to handle, further reducing your costs. In addition, by deploying
twice as many radiating elements, you improve network coverage and minimize the
number of holes.
Figure 6. Wireless repeater
By adding three Over-The-Air repeaters to the base station, the cell coverage
footprint can be enlarged to 53 squire km, at an added cost of only $90,000. In capital,
the savings would be 30% and the underutilized capacity would be virtually eliminated.
Here are some comparisons of capital cost of items used in Base Station and Repeater
[26]. The cost of items of repeater is much lower than those of base stations.
30
Table III. Capital Cost of items in base stations and repeaters
ITEM
REAL ESTATE LEASE
ELECTRICITY
($0.10/KWH)
HARDWARE
MAINTENANCE
SOFTWARE
MAINTENANCE
T1 BACKHAUL (75 MI)
DIVERSITY BACKHAUL
TOTAL
NPV 1 YEAR
5 YEARS (PCS CDMA
ESTIMATES ONLY)
1.12.
BASE STATION
$1,000
$430
REPEATER
$500
$20
$150
$50
$20
$5
$2,000
$2,000
$5,600
$65,066
$289,663
$25
NOT REQ'D
$600
$6,971
$31,035
Conclusions
In this report, wireless repeater technologies were comprehensively investigated. The
advantages and issues of wireless repeaters were also pointed out. Other issues related to
the market of wireless repeaters were also analyzed. Due to their advantages, it is
believed that wireless repeaters continue to be promising equipment of wireless networks.
31
2.
Pico-BTS
2.1.
Overview
Large scale multi-sector base stations have been the main stream in the current mobile
telecommunication systems. However, there is an explosive growth in demand for indoor
cellular coverage with higher capacity. Traditional macro- and micro-cellular networks
require real estate lease and have higher power consumption. Hence, it is not easy to
satisfy the growing demands for indoor mobile applications with low cost, high
bandwidth, and great flexibility through traditional cellular networks. Pico-cellular
solutions can offer higher capacity and better service quality inside buildings such as
corporate premises, congress centers, hotels, and lounges. This requires a base transceiver
station (BTS) that is compact, and capable of providing at least the same service quality
as the outdoor networks. Pico-cell base station systems are also suitable for shadowed
areas and over-populated subscriber regions.
In this chapter, we analyze the technology of pico-cell BTSs, their characteristics
and deployment.
2.2.
2.2.1.
Technology and Standardization of pico-BTS
Characteristics and Advantages
Currently, pico-cells are the smallest radio cells defined in mobile networks. They often
extend to only a few hundred meters in diameter. Pico-BTSs are used to create pico- or
in-building cells. These cells have the following characteristics:

Very low delay

Low speed mobile subscribers

Small size

Usually deployed at hot spot traffic areas like convention centers, shopping malls,
and train stations to provide high capacity.
The advantages of pico-BTS can be summarized as follows:

Cost efficient manufacturing:
Pico-BTSs are of small size and modular design. They can be manufactured in high
volumes. Therefore, the manufacturing cost is reduced.

Easy and flexible installation:
The antennas of macro-cell base stations are usually mounted above the rooftop level
of surrounding buildings. However, pico-BTSs can flexibly be installed on the wall,
utility poles, and many other places.
32

Cost savings associated with network design and operation:
Compared with macro-cellular networks, the pico-cellular solutions do not require
towers or shelter to protect the equipment. This feature helps to reduce the cost
associated with the deployment of the infrastructure.

Reduction in site construction and field maintenance:
Since pico-cells have small sizes, and pico-BTSs are usually installed in-doors, field
maintenance cost for pico-BTSs is reduced.

Time-saving implementation:
The design does not include the time-consuming procedure of applying approval from
local city zoning committees for the construction of towers and outdoor shelters used
to house cellular antennas. It is easier for the pico-BTS to get approval because of its
small size.
2.2.2.
Components and functionality
The purpose of pico-BTS is to modulate, amplify, filter, and transmit signals. It can also
relieve capacity in hot spot areas. The major components of a pico-BTS are shown in
Figure 7.
Controller
Modem
Transceiver
RF
Front-end
.
.
.
IF/BB
Interface
Transceiver
.
.
.
Backhaul
Interface
Modem
DC Power, Time-frequency
Figure 7. Major components of a pico-BTS
33
BSC
The key functionality of pico-BTS includes:

RF transmission and reception,

Frequency up and down conversion,

Modulation / Demodulation,

Interface to BSC,

Call processing and management.
2.2.3.
Current Progress of Pico-BTS
The latest trend in pico-BTS has the following focuses:

Compact, low cost, quick installation, and less maintenance,

Smart antenna to help to increase capacity,

Software defined radio:
o One platform for multiple protocols,
o Flexible upgrades, longer life cycle, and quick to the market with new services.
Table IV gives a summary of the latest CDMA pico-BTS products. It shows a
comparison of the features for each pico-BTS, which including dimension, weight,
capacity, RF output power, and antenna configuration.
Table IV. Comparison of CDMA pico-BTS products
SCTM 601
Pico-BTSTM
Flexcent
Qcell 500
by Motorola
by Samsung
by Lucent
by Qualcomm
Dimension
(inch)
34x28x12
RMU 18x20x10
34.6x18.25x12
26x15x8
Weight (lb)
210
110
75
PRU15x12.5x6
RMU 80
PRU 45
Capacity
(channel
elements)
16
64
40
64
RF Output
Power (W)
5
5/10
10
10
Configuration
Omni
Omni, 3 sector,
6sector
Omni
Omni
34
2.2.4.
Standardization
The European Telecommunications Standards Institute (ETSI) developed several
standards and technical specifications on Base Station Systems (BSS) for GSM and third
generation wireless systems [27], [28], [29], [30]. In [27], the requirements for the
transceiver of the digital cellular telecommunications systems GSM are presented. This
standard defines Radio Frequency (RF) characteristics for the Mobile Station (MS) and
BSS. The BSS contains either a normal BTS or BTSs at micro-cells and pico-cells
(micro-BTS, pico-BTS). In [28], the RF test methods and conformance requirements for
GSM 900 and DCS 1800, PCS 1900, GSM 850, MXM 850 and MXM 1900 BSSs are
specified. These specifications are derived from the core GSM specifications. This
document is applicable to BSSs meeting the requirements of both GSM Phase 2 and
GSM Phase 2+. In [29], the requirements for transceivers (BTS, micro-BTS, and picoBTS) in a 136HS system are defined. In [30], the requirements for synchronization on the
radio subsystem of the digital cellular telecommunications systems are presented.
The International Telecommunication Union (ITU) developed a family of
standards for the 3G systems. Leading 3G standards are based on CDMA technology,
though there are other standards based on FDMA/TDMA and TDMA-SC). Two main
standards based on CDMA technology for 3G are Wideband CDMA (WCDMA) and
CDMA2000. WCDMA standards are currently under review by 3GPP, 3GPP2 as well as
Operators’ Harmonization Group. Till now no single base-station model is the standard.
WCDMA base-station products started with 15-channel model designs. Recently
products with 50- or 60-channel models have been produced by manufactures.
2.2.5.
Frequency Allocation
The GSM standard contains several subsets:

P-GSM (Primary GSM) uses the channels 1-124

E-GSM (Extended GSM) uses the channels 975-1023 and 1-124

R-GSM (Railways GSM) uses the channels 955-1023 and 1-124

DCS 1800 (GSM 1800) uses the channels 512-885

PCS 1900 (GSM 1900) uses the channels 512-810
The frequency bands for GSM BSS defined in [27], [28], and [29] are given in
Table V.
Table V. Frequency bands for GSM base station systems
P-GSM 900
E-GSM 900
R-GSM 900
DCS 1800
GSM 850 and MXM 850
PCS 1900 and MXM 1900
TX:
935 MHz to 960 MHz
925 MHz to 960 MHz
921 MHz to 960 MHz
1805 MHz to 1880 MH
869 MHz to 894 MHz
1930 MHz to 1990 MHz
35
RX:
890 MHz to 915 MHz
880 MHz to 915 MHz
876 MHz to 915 MHz
1710 MHz to 1785 MHz
824 MHz to 849 MHz
1850 MHz to 1910 MHz
The BSS manufacturers declare the specific operating frequency range of their
devices. This operating frequency range should be within the frequency bands defined in
Table V. This frequency range comprises the transmit and receive operating bands. A
BSS may support DCS 1800, PCS 1900, MXM 1900, GSM 850, MXM 850 and one of
the GSM 900 bands, but should not be defined as supporting more than one of the GSM
900 bands [27].
The pico-BTS is an extension of the micro-BTS concept to the indoor
environments. Micro-BTS and pico-BTS are different from a normal BTS in two ways.
First, the range requirements are less strict, and the close proximity requirements are
more stringent. Second, the micro-BTS and pico-BTS are required to be of small size and
of low complexity to allow deployment in large numbers. Therefore, the micro-BTS and
pico-BTS need a different set of RF parameters to be specified to guarantee their
requirements [27].
Many pico-BTS products support GSM 900, DCS 1800 and PCS 1900 frequency
bands, such as the BS-242 Pico by SIEMENS supports GSM 900, DCS 1800 and PCS
1900; the sub-pico CDMA IP-BTS by Halfdome Systems supports PCS 1900; and RBS
2401 Indoor Base Station by Ericsson supports GSM 900 and DCS 1800.
Different frequency bands are allocated in different parts of world for third
generation mobile services. Figure 8 gives detailed information about the frequency
allocation for IMT-2000. The frequency of operation of WCDMA base-stations will be as
per the frequency allocated in that particular region. Base station specifications for
WCDMA are yet to be finalized.
2.2.6.
Power Management
For pico-BTS, the manufacturers declare the rated maximum power at the antenna
connector. The class of a pico-BTS is defined by the highest output power capability for
8-PSK modulation, and the output power should not exceed the maximum output power
of the corresponding class. The power classes of pico-BTS are in Table VI.
Table VI. Pico-BTS power classes
TRX Power Class
P1
Pico-BTS Maximum Output Power
GSM 900, GSM 850 &
DCS 1800, PCS 1900 &
MXM 850
MXM 1900
(>13)-20dBm
(>16)-23dBm
The tolerance of the actual maximum output power of the BTS can be pm 2 dB
under normal conditions and pm 2.5 dB under extreme conditions. In order to be able to
hop between any defined power levels on a time slot, the dynamic power control may
optionally be implemented in GSM pico-BTS according to [31].
2.2.7.
Interference
The spectrum allocation varies in different parts of the world. The availability of
spectrum also varies greatly from operator to operator. Currently, no base station
hardware supports all of worldwide frequency assignments [32]. Moreover, the addition
36
of spectrum for 3G applications adds more complexity to the task of designing base
station hardware. Figure 7 shows the worldwide spectrum allocation [33], which is a
reference for BTS designers.
Figure 8. Worldwide spectrum allocation
Interference is the limiting factor for the capacity of wireless systems. There are
three types of interference:
 Co-channel interference: produced by users who transmit in the same frequency
channel.
 Adjacent channel interference: produced by users who transmit in the neighboring
frequency channels.
 Out-of-band interference: produced by non-linearities.
Due to the frequency reuse nature in cellular systems, there is co-channel
interference. Co-channel interference arises when the same carrier frequency is used in
different cells. In this case, the power density spectra of the desired and interfering
signals completely overlap. So, in narrowband systems, intense frequency reuse is not
possible due to co-channel interference which degrades the quality of the received signal
to intolerable levels.
Frequency reuse also introduces adjacent channel interference. This type of
interference arises when neighboring cells use carrier frequencies that are spectrally
adjacent to each other. In this case, the power density spectrum of the desired and
interfering signals partially overlap. Adjacent channel interference is usually avoided by
means of selective filters. The system designer should not assign contiguous channels to
the same cell. Adjacent channels are usually spaced by 6 other channels (not used in the
cell).
37
2.2.8.
Environmental Conditions
ETSI defined the following environmental conditions as the requirements for the BSS
equipment [27]:
Normal environmental conditions:

Temperature Range: +15 to +35°C

Relative Humidity: 35% to 75%

Air Pressure: 86 kPa to 106 kPa
Extreme typical operating temperature ranges are:

Indoor Temperature Range: -5°cto +50°C

Outdoor Temperature Range: -40°cto +50°C
In addition, the BTS should not make ineffective use of the radio frequency
spectrum and exceed the transmitted signal level as defined in [31] for extreme operation.
2.2.9.
Major Suppliers and Products
Many companies have pico-BTS products. Here we list some of the major products.
2.2.9.1.
BS-242 Pico by SIEMENS
BS-242 Pico-BTS is a new base station solution for indoor applications. It allows easy
and flexible deployment in any indoor segment. It provides flexible coverage areas and
capacity allocation, easy modification and extension of existing deployments, and fast
installation. The decentralized architecture comprises of one server (core part) and up to
24 agents (remote TRX). Multi-carrier cells may be built simply by configuration. The
main features of BS-242 Pico-BTS are:

E-GSM 900/1800/1900

Dual band support by the same server

Internal and external antenna

RF frequency hopping

Output power up to 200 mW at antenna connector
2.2.9.2.
RBS 2401 Indoor Base Station by ERICSSON
Ericsson's RBS 2401 Indoor Base Station is a self-contained design. It can reduce the cost
of providing high-quality coverage for wireless office services in public buildings. It is
small, consumes 65 Watts, and has enough capacity to serve around 100 typical office
users. It is compatible with advanced GSM services. It supports GSM 900 and 1800 MHz
frequencies, and fits into Hierarchical Cell Structure schemes. It may also be deployed as
part of Ericsson's integrated GSM-over-IP business communications solution.
38
2.2.9.3.
Sub-Pico CDMA IP-BTS by Halfdome Systems, Inc.
This BTS enables service providers to extend the IP network to the RF unit. Service
providers are able to offer high bandwidth IP services, including Internet access, to its
mobile customers. This BTS supports better quality soft handoff procedures and
voice/data services in an in-building environment. The sub-pico CDMA IP-BTS supports
PCS 1900 and has an output power of 25 mW at antenna connector.
2.2.9.4.
PicoBTS (TM) by Samsung
Samsung received the "Infrastructure Product Innovation Award" from the CDMA
Development Group by its PicoBTS product in 1998. The PicoBTS is designed for the
CDMA radio platforms. It provides open architecture to make CDMA an affordable
option for smaller carriers. It allows the operators to fit their design needs while reducing
initial network deployment costs. The PicoBTS provides the operators with a small, yet
high capacity platform allowing for maximum deployment flexibility. It is designed for
both indoor and outdoor applications, and is available for omni and sector deployments.
It is the first CDMA product of its size to incorporate dynamic channel allocation and
feature up to 64 channel elements that may be appropriate for any sector and/or frequency
in a multi-carrier configuration.
The main features of the PicoBTS are:

Air-interface: IS-95 A/B

Operating frequencies: PCS and cellular frequencies

Configurations: omni multi-carrier, 2-sector multi-carrier, 3-sector single carrier,
indoor or outdoor

Capacity: 64 channel elements
2.3.
Types of Pico-BTS
According to the installation location, pico-BTSs can be categorized as indoor pico-BTS
and outdoor pico-BTS. There are three types of pico-BTSs according to the underlying
air interface:

pico-BTS supporting GSM (900/1800/1900)

pico-BTS supporting TDMA (IS-136)

pico-BTS supporting CDMA (IS-95)
2.4.
Main Target Market Forecast
The pico-BTS technology is currently in use, and its future is even more promising. The
growth of the wireless population along with the increasing demand for higher bandwidth
due to new wireless applications pushes the network operators to have smaller cells.
Smaller cells increase system capacity, and provide higher bandwidth to the subscribers.
On the other hand, smaller cell sizes imply more frequent handoffs. In order to avoid the
39
adverse effect of frequent handoffs, the pico-cells must be located at hot spots like
downtown areas where the subscriber density is high and mobility is low.
2.4.1.
Discussion of the Current Market Segments
The pico-BTS technology is being currently used for 2G systems at hot spots. It is also
being considered for the 3G cellular systems. The major application of the pico-BTS
technology is Samsung's award-winning product. Samsung Telecommunications America
and Tecore, Inc. have merged their efforts to offer a modular solution to small second-tier
PCS operators in North America. They have integrated Samsung's PicoBTS with Tecore's
AirCore Platform MSC and transmission system. The decreased cost of the pico-BTSs,
due to economies of scale, has enabled cdmaOne to compete with TDMA and GSM
networks. Thus, it has become economically reasonable for the rural operators to invest
in CDMA systems. Tecore's switching center is scalable from 500 to 100,000 subscribers.
The PicoBTS, coupled with Tecore's switching center, allows small operators to affiliate
with brand-name carriers while operating their own networks.
The Samsung-Tecore solution was initially developed for the US market where
cdmaOne and PCS networks are expected to reach 28.2 million subscribers by 2002 [36].
However, the fact that Samsung is taking this product to South Korea, and Telstra is
replacing its AMPS network with cdmaOne shows that the international market for picoBTS is expanding. Samsung has also made a contract with AirTouch Communications
(now Vodafone AirTouch Plc which operates in 28 other countries) in May 1999 for five
years to deploy CDMA PicoBTS and BSC in the US.
2.4.2.
A Forecast of the Target Markets and Estimated Market Size
One of the major problems cellular operators encounter is getting approval from the local
city committees for the construction of towers and outdoor shelters for the base stations.
Pico-cell solution is different from the traditional micro- and macro-cell solutions in
terms of deployment since pico-BTSs can be installed inside privately-owned buildings.
The deployment characteristics reduce the problems encountered with the local
regulatory agencies. They also decrease field maintenance costs by satisfying A/C and
power requirements, and avoiding tower and shelter rents.
Samsung has invested over $200 million in the US market as a proof of its belief
in the potential of pico-BTS technology. Pico-BTSs will be integrated with other
networks in the future to bridge the gap between 802.11b WLANs and 3G cellular
networks. Enterprises can install pico-cells in their premises and integrate it with their
local PBX switchboards. This model will improve the in-building signal reception. The
enterprises can utilize this model to switch the calls made in the office as local calls
through their local PBXs. There will be a seamless handoff to the cellular network when
the employee leaves the premise.
2.5.
Health and Safety
People who live or work close to BTSs are concerned about health and safety issues. The
government of United Kingdom investigated possible health effects posed by mobile
40
phones and base stations, and published the results as a report [34]. The conclusion in the
report is: "The balance of evidence indicates that there is no general risk to the health of
people living near base stations, on the basis that exposures are expected to be small
fractions of guidelines."
Although none of the recent research activities have concluded that exposure to
the RF fields from mobile phones or base stations causes any adverse health
consequence, radio waves above a certain signal level can cause heating effects to the
body. International guidelines have been set to keep exposure to radio waves below that
signal level. Network operators should comply with these international guidelines. In
addition, the base station antennas emit RF beams that are typically narrow in the vertical
direction but broad in the horizontal direction. The network designer should mount the
antennas at a certain height to ensure the RF field intensity at the ground directly below
the antenna is low. The RF field intensity decreases as one moves away from the base
station. Since the size of macro- and micro-cells is larger than the size of pico-cell, the
base stations for the larger cells transmit at higher signal levels. Therefore, the
individuals located close to such base stations will be subject to higher signal levels.
According to David Allen, Director of Wireless Systems for Samsung
Telecommunications America, Inc, "environmental concerns are ever-present when
attempting to gain construction approval from various government agencies," in addition
to the health and safety concerns. He has also mentioned that the pico-BTS is
"aesthetically pleasing to the eye and extremely unobtrusive in city or rural landscapes,"
because of its small size [37].
Overall, the network operator should take electromagnetic energy, safety level,
and safety distances into consideration and follow the health and safety-based guidelines.
2.6.
Technology Development Prospect Analysis
As the wireless multimedia communication becomes more popular, there is a trend in
developing 3G base stations that enable users with various services. Making voice calls,
surfing the web, checking e-mails, participating in video-conferences, and accessing a
wide range of new services from their wireless devices are examples of such services. It
is expected that the pico-BTS technology will follow the development of 3G wireless
systems and improve in the following aspects:

3G CDMA pico-BTS
The underlying 3G innovation is Wideband Code Division Multiple Access
(WCDMA) technology. To deliver the promise of WCDMA, 3G pico-BTS must be
able to handle greater capacity, support higher data rates and multimedia standards,
while reducing the cost and the power consumption. The difference in the bandwidth
requirements of different services like voice, data, and video must also be considered
in the design.
For 3G pico-BTSs, high channel density must be accompanied by low power
consumption. Components of pico-BTSs should consume less power, dissipate less
heat, and be packed more densely. In addition, pico-BTSs should be reliable to keep
41
maintenance costs down. All of these requirements place great demands on the
performance, scalability, programmability, and power efficiency of 3G pico-BTS.
Overall, the 3G pico-BTS infrastructure requires high performance and better cost,
space, and power consumption efficiency.
Several companies are working on 3G CDMA pico-BTSs, such as Samsung, Hyundai
Electronics, and Texas Instruments.
ETSI selected W-CDMA and TD-CDMA as the radio interfaces for the outdoor and
indoor environments, respectively. In [106], a link level simulation is provided to
compare W-CDMA and TD-CDMA systems. Two vehicular and two indoor to
outdoor scenarios with different channel responses are considered in the simulations.
Voice and data (circuit-switched and packet-oriented) services are considered for both
air interfaces. The simulation results are summarized in Figure 9.
Figure 9. Link-level simulation results [106]
The round trip delay of the power control algorithm in the TD-CDMA mode is higher
than the delay in W-CDMA mode. Therefore, the link performance in the TD-CDMA
mode is more influenced by the mobile speed than the W-CDMA mode. Furthermore,
the absence of the antenna diversity in the downlink causes the link performance to be
downgraded with respect to the uplink. This is especially true for circuit-switched
data service.

Wireless Access to IP Network
The growth of the Internet and the success of mobile wireless networks lead to
increasing demand for mobile wireless access to Internet applications. The IP-based
pico-BTS enabling broadband multimedia mobile communications is a great solution
for this demand. As we introduced previously, the product Sub-Pico CDMA IP-BTS
from Halfdome Systems, Inc. [35] is an IP-based CDMA pico-BTS. The system
architecture is shown in Figure 10.
42
Figure 10. IP radio access wireless network
As shown in this figure, the pico-BTS is an element in the overall IP-based radio
access network. The wireless access gateway connects the wireless network and the IP
network to enable high bandwidth IP services to mobile users. With Internet access, high
quality voice and data services are supported in an in-building environment.
Wireless IP communication is a promising field for future technology
improvements. IP-based pico-BTSs have great potential in the future market. The need
for pico-BTS will increase with the emerge of the next generation wireless networks. The
cell size in the next generation wireless networks will decrease due to the many reasons.
The increase in the number of subscribers will pose the need for more capacity. The
system capacity can be increased by smaller cells, and frequency reuse. Furthermore, the
increase in the bandwidth requirements per user can be satisfied in smaller cells and
shorter distances.
Pico-BTSs will employ new technologies like the OFDM-CDMA technology in
the air interface to provide high bandwidth. QoS provision will also be provided in the air
link of the next generation networks.
2.7.
Service Analysis
Providing in-building communications services using wireless technology and pico-cell
base stations is a feasible alternative to wireline networks. It offers many advantages,
including cheaper and easier installation since it does not require the laying of cables, etc.
It can also provide as much bandwidth as a wireline network. The deployment of wireless
networks will be much faster than that of wireline networks. Thus, wireless networks are
more suitable for temporary events like exhibitions. Furthermore, it is the only solution
for places such as historic buildings where laying cables or drilling holes is not allowed.
43
Moreover, wireless network infrastructures such as 2.5G and 3G can be constructed using
pico-cell base stations in buildings. In the near future, broadband multimedia services
will be available over Internet as the IP convergence solution is getting more interest and
the IP technology is moving toward the edge in the radio access network (RAN) [42].
2.7.1.
Current Services (2.5G/3G)
The deployment of pico-cell base stations enables cellular/PCS operators to offer
enhanced system capacity, coverage. Pico-BTSs also enable high quality voice and high
speed data services as in GPRS, cdmaOne and cdma2000 [39]. The users inside the
buildings can use their mobile phones to benefit from high quality voice and additional
services as well as data transmission capabilities.
2.7.2.
Future Services
Pico-cell base stations will also enable multimedia services, voice and video mail,
wireless virtual private network (VPN), and other competitive features with QoS
guarantee. Additionally, it is possible that location-aware services will be provided
considering the small cell size of pico-cellular networks which means better knowledge
of the user's location. A pico BTS can provide the location information of enough
precision for location-aware services without additional cost. In the future, Internet
technology will also be immediately available for cellular transmission [42]. Thus, the
mobile users in the buildings will have complete access to the Internet using their mobile
devices, and various types of multimedia services will be provided through Internet and
corporate LANs.
44
2.8.
Network Design Plan Analysis
Figure 11. In-building network
Given the expense and limitations of physical cabling, the idea of using wireless
technology and pico-cell base station to construct an in-building network becomes an
obvious alternative. In a wireless in-building pico-cellular network, the working place is
partitioned into pico-cells defined by floors and major walls. Such a system can be
implemented to save time and cost due to cabling. Figure 11 shows an example of an inbuilding wireless network using pico-BTS. The deployment approaches in constructing
such an in-building network can be mainly categorized into two approaches according to
the front-end used.
2.8.1.
Distributed Antenna Approach
The deployment for the distributed antenna system will involve an arrangement of central
base stations feeding out to several of antennas over coaxial or fiber cables. The antennas
could be directional or omni-directional depending on the need. Figure 12 shows how an
in-building deployment is achieved by the distributed antenna approach. It shows the
base station located in the basement feeding out to the distributed antennas of the
building.
45
Figure 12. Distributed antenna
This approach for deploying wireless in-building network involves lengthy cell
and frequency planning and the installation of distributed antennas using coaxial or fiber
cables [41]. A typical installation can take several weeks and can cause a certain degree
of disruption to the workplace.
The typical decisions that a system integrator would consider in an in-building
installation can be summarized as follows:

Whether the building will be supported by external antennas or it will require
internal base stations.

The coverage and level of service that will be needed.

The number of cells and frequency band required to meet the specification.
In order to decide on these items, the system integrator will need to perform test
measurements on the site to find out how RF signals attenuate throughout the building.
The system can effectively be integrated and optimized by test measurements. This
approach might not be well suitable for use in events requiring temporary deployment for
it involves cabling work to some degree. It might not be able to deliver very large
capacity because it depends on the central BTS's multiplexing capability.
46
2.8.2.
Distributed BTS Approach
Figure 13. Distributed BTS
The distributed BTS approach involves using a BTS as the front end to the wireless inbuilding network. While this is not the most cost-effective method for an antenna could
be cheaper than a BTS, it is the most robust solution for deploying a wireless in-building
network because it provides a capacity as large as the in-building system needs [40].
Additionally, as lower cost pico-cell BTSs will be available from various vendors, this
approach will become more feasible. Figure 13 shows how an in-building deployment
can be done with this approach. It shows the base stations distributed in the building.
Using a BTS as the front end of the system provides the flexibility to allocate
capacity as needed. This approach also allows engineers to conduct frequency planning
on a cluster basis with the rest of the external macro system, allowing the in-building
system to be seen as its own separate and independent site within the carrier's system.
Moreover, it is possible to introduce autonomous cell and frequency planning through
extended operating and maintenance (O&M) functionality. The ability of each pico BTS
to listen to the network and provide O&M information to a central controller will result in
the production of a virtual map of the distributed BTS network and ensures efficient use
of allocated frequencies within the building. With autonomous cell and frequency
planning, each distributed BTS can adjust its power level and frequency to define its
position in the network. It can also be used to minimize interference with the external
macro cellular networks.
Test measurements of the building will still be required but to a much lesser
degree than the distributed antenna approach. The distributed BTS can be deployed
exactly where the capacity is needed. Furthermore, by using standard IP autoconfiguration protocols, the distributed BTS can locate the central base station controller
(BSC) and then register and authenticate a secure connection. Upgrades and addition of
47
capacity can be achieved by simply adding another distributed BTS, which, in turn,
causes the internal network to recon to accommodate the new distributed BTS. With this
approach, the installation process can be done in days.
2.9.
Network Security Plan
Data security itself is a fundamental design consideration for any RF-based network
technology. In wireless in-building network systems, there could be two ways in which
data might be intercepted:

Out of the system.

Inside the system.
Preventing effective reception of system data by an outside receiver is an inherent
benefit of a technology allowing spectrum reuse within a relatively short distance. To
allow reuse of the same frequency by a system nearby, system power level is kept very
low. Additionally, it needs to take advantage of the propagation characteristics of the
system RF as used in the in-building system. With their reflectivity and ability to
disperse, the low-power system signals provide whole coverage within the in-building
pico-cellular environment, yet are greatly attenuated by continuous barriers such as
building floors and walls and dissipate rapidly with distance. Moreover, the multipath
problem will make the signal incoherent to an outside receiver.
To protect the in-building network system from an inside attack, a controller node
concept could be employed. In this system, every user node is required to register with
the controller node and authenticate a secure connection before it starts communicating.
Each user node not only needs to register and authenticate, but also has to request and be
authorized to transmit and receive. Any node without authorization that tries to
communicate will be excluded from the system. User nodes can neither transmit nor
receive unless they are told to do so by the controller node. This operational protocol will
be buried securely within the source code of the system.
2.10.
Network Deployment Scenarios and Analysis
A cellular operator considers how the subscribers are distributed over the service area,
and their movement patterns in network design. Thus, the number of handoffs is
minimized, and the system capacity and coverage are maximized. According to these
criteria, the typical deployment scenario for a cellular operator in a major city is to cover
the rural areas with macro-cells, and urban areas with micro-cells. Such a deployment
provides coverage with fewer base stations in rural areas, reducing the network cost.
However, deploying macro-cells in urban areas causes low system capacity in densely
populated areas. Therefore, micro-cells are deployed in urban areas, resulting in more
handoffs. Although micro-cells increase system capacity, they cannot solve the capacity
and coverage problems completely. There will still be dead spots inside the micro-cells
with almost no coverage. Such dead spots will typically exist inside the buildings where
the walls obstruct the radio signals.
48
In order to overcome the problem of dead spots and increase system capacity,
another possible scenario is to place pico-BTSs inside the buildings. In this scenario,
pico-BTSs are placed at different floors of a building in which the coverage is to be
improved (Figure 14). Although the building may be inside another cell, the subscribers
in the pico-cells will have better signal reception from the pico-BTS, and communicate
with the pico-BTS. Although the pico-cells are very small, there will not be frequent
handoffs since the subscriber speed inside the building will be very low.
Figure 14. Alternative deployment with pico-BTSs
2.11.
Network Cost Analysis
There are three basic differences between the two scenarios, given in Section 2.10, that
affect the network cost:

There are less base stations in the typical deployment, therefore the total investment
in the equipment will be lower.

In the alternative deployment scenario, the pico-BTSs are placed inside the building
where better coverage is required. Therefore, the cost of real estate to shelter the base
stations and establishing the towers in the typical scenario is avoided. Thus, the
overall cost of the alternative scenario will not be high.
49

Since the system capacity is increased and coverage is improved with the alternative
scenario, the revenues of the cellular operators increase.
As a consequence of the items above, the gain obtained by deploying pico-BTSs,
in places where feasible, surpass the cost of the deployment. Therefore, pico-BTS
deployment is a good solution as long as the number of pico-BTSs and their locations are
determined after careful study.
2.12.
Conclusions
In this chapter, the technology of the pico-BTS has been presented from both of the
technological and business perspectives. Some technical aspects of pico-BTS including
standards, frequency allocation, power, and interference have been discussed in detail.
Current and future technological development prospects of pico-BTS and its market
forecast have been investigated.
For cellular networks deployed in some challenging environments such as
mountains or highways wireless repeaters seem to be more suitable due to its cost
efficiency with respect to the coverage it provides. For instance, cellular coverage might
be increased with the use of wireless repeaters instead of costly deployment of base
stations in mountains. In highways, on the other hand, high coverage solutions must be
deployed in order to maintain the acceptable handoff rate in network. Pico-BTS is not an
efficient technology for those areas due to its relatively low coverage.
In-building network design, however, might well take advantage of the higher
capacity and service quality pico-BTS offers. Wireless repeaters along with the pico-BTS
might be utilized together for large in-building areas to obtain cost efficient, high
capacity and increased service quality cellular network solutions. A base station per
building, wireless repeater for each floor, and pico-cell BTS for each corridor or large
meeting hall might be a simple network deployment scenario in which wireless repeaters
and pico-BTS coexist.
50
3.
3.1.
Wireless LAN
Overview
In local areas such as business buildings, campuses, malls, and homes, the everincreasing demands of wireless access to next generation networks continuously motivate
the quick evolution of wireless local area networks (WLANs). Via WLANs, users can
access high speed multimedia applications anywhere at anytime. Due to the high speed
and multiple traffic types that are expected to be supported in the future WLANs, last
mile issues in a local area network (LAN) environment will be solved at the same time.
In order to achieve the objectives of easy implementation, low cost, and wide user
acceptance, WLAN generally work in industrial, scientific, and medical (ISM) band,
which is un-licensed and available for public. Currently, several types of WLAN products
have already existed. They belong to different standardization groups and can be
categorized according to their different protocol standards. Typical WLAN standards or
draft proposals include IEEE 802.11 [9], [44], [45], Bluetooth [46], [47], HomeRF [48],
IEEE 802.16 [10], HiperLAN [49], [50], and many others [51], [52].
To date, several challenging issues still exist in WLANs. Compared to 2G
wireless networks, current WLAN products are able to support data applications. Some
products can achieve very high data rate, e.g., the rate of IEEE 802.11 WLANs can be as
high as 11Mbps, while some products such as Bluetooth can only achieve medium speed
data rate. Moreover, current WLAN products are weak in providing real time services. As
an example, IEEE 802.11 products, which are based on the CSMA/CA protocol [9], are
unable to provide quality of service (QoS) guarantees for voice, video, and other real time
services. Thus, IEEE 802.11 working group E is still working QoS enhancement for
IEEE 802.11 WLAN [53]. HomeRF products cannot support other real time service
except low speed isochronous applications [48]. Another issue of WLANs is that
interference between different types of WLANs can greatly degrade the performance of
WLAN [54]. Moreover, the interoperability between WLANs needs to be paid attention
to. Otherwise, the global communication, which is one of the objectives of the next
generation communication systems, cannot be achieved.
Although WLANs are still being researched in order to have more advanced
features, basic techniques are mature enough for deployment. WLANs are now being
widely deployed. It is expected that the market of WLAN will be huge because WLANs
will provide tetherless, high speed, and QoS-guaranteed last mile access to backbone
networks such as next generation Internet.
In this chapter, we give a comprehensive investigation of WLAN technologies. In
Section 3.2, we first analyze the functions, techniques, and standards of wireless
repeaters. Then, current applications of WLANs, interference, and environmental issues
are investigated. In the final part of this section, major suppliers of WLAN are presented.
In Section 3.2.7, types of WLAN are categorized. Characteristics of these types of
WLAN are also addressed in this section. The target market forecast and technology
development prospect are reported in Sections 3.4 and 3.5, respectively. Interworking and
integration with IMT-2000 are discussed in Section 3.6. Services provided by WLAN
51
technologies are presented in Section 3.7. Network design plan and network deployment
technology based on WLAN are analyzed in Sections 3.8 and 3.9 respectively. In
Sections 3.10 and 3.11, the network deployment scenarios and cost analysis are
presented.
3.2.
Technology, Standardization, Present Conditions of
WLAN
3.2.1.
The WLAN Technology and Standards
Currently, different types of WLANs coexist. For some WLANs, standards have been
finalized. However, due to the increasing demands on the next generation communication
systems, more research efforts are necessary in order to enhance the performance of these
products. Thus, it is expected that standards with more advanced features will be
proposed for these WLANs. For certain types of WLANs, proposals have been proposed,
but research is still being carried out to finalize the standards. Finally, some types of
WLANs are still in the start-up phase. Lots of research efforts are required in order to
have a standard. In this subsection, the investigation is focused on the WLANs that have
been widely accepted or researched. In particular, we analyze the WLANs such as IEEE
802.11 [9], Bluetooth [46], HomeRF and shared wireless access protocol (SWAP) [48],
and HiperLAN/2 [50]. To investigate these typical WLANs, we focus on the technologies
in the data link layer. Other issues such as frequency spectrum, bandwidth, and
propagation characteristics of WLANs will be described in Section 3.2.3, and
interference issues are discussed in Section 3.2.4.
3.2.1.1.
IEEE 802.11
IEEE has developed several specifications in the Wireless LAN (WLAN) 802.11 family.
Among them, 802.11a and 802.11b use Carrier Sense Multiple Access with Collision
Detection (CSMA/CD), as the medium access protocol. It means that if a card has
something to send, it will listen until no other card is transmitting, then starts
transmitting, and listens if no other card starts transmitting at the very same time. If
another card began transmitting it will stop, wait for a random interval and try again. If a
source station has a data packet to send, the station checks the system to see if the path
medium is busy. If the medium is not busy, the packet is sent; if the medium is busy, the
station waits until the first moment that the medium becomes clear.
IEEE 802.11 standards activities include followings:

802.11a - 5GHz- Ratified in 1999

802.11b - 11Mb 2.4GHz- ratified in 1999

802.11d - Additional regulatory domains

802.11e - Quality of Service

802.11f - Inter-Access Point Protocol (IAPP)

802.11g - Higher Data rate (>20mBps) 2.4GHz
52

802.11h - Dynamic Frequency Selection and

Transmit Power Control mechanisms

802.11i - Authentication and security
In the IEEE 802.11 standard, the physical layer and the MAC protocol are
specified [9]. The MAC protocol has two operation modes, i.e., distributed mode and
coordinated mode. As shown in Figure 15, the distributed coordination function (DCF)
works in a distributed fashion and is based on CSMA/CA protocol. The point
coordination function (PCF) is implemented on top of DCF in order to support real time
traffic. PCF is based on polling which is controlled by a centralized point coordinator.
Figure 15. Protocol architecture of IEEE 802.11
In addition to PCF and DCF, three interframe spaces (IFS) are defined in the
IEEE 802.11: short IFS (SIFS), DCF-IFS (DIFS), and PCF-IFS (PIFS). The length of
SIFS is the shortest, and PIFS has a shorter length than DIFS. Normally, SIFS is used for
CTS and ACK messages; and CIFS and PIFS are for asynchronous data and real-time
traffic, respectively. Based on IFS, DCF, PCF, and the mechanism of CSMA/CA, the
main operation procedures of the MAC protocol is shown in Figure 16. It actually
follows the mechanism of using RTS/CTS to avoid collisions and hidden nodes.
Figure 16. Main operation procedures of the IEEE 802.11 MAC protocol
The IEEE 802.11 can support both data and real time traffic. However, their
design is not QoS oriented since only priority is assigned to different types of traffic.
Also, in order to support real time traffic, a centralized coordinator is required, which is
infeasible in some wireless LANs such as ad-hoc networks. Thus, in [55], a reservation
CSMA/CA is proposed to support multimedia traffic over mobile ad-hoc networks. IEEE
802.11 Working Group E [53] is also working to enhance the QoS capability of IEEE
802.11.
53

802.11 Compatibility
While 802.11a and 802.11b share the same MAC layer technology, there are
significant differences at the physical layer. 802.11b, using the ISM band, transmits in
the 2.4 GHz range, while 802.11a, using the -NII band, transmits in the 5 GHz range.
Their signals travel in different frequency bands allowing both technologies to
operate without interfering with each other, it’s even possible to operate both on the
same network concurrently. This can allow both 802.11b and 802.11a to operate
using the same access points.

Interoperability
To ensure crossvendor interoperability [91], WLAN purchasers can look for the WiFi symbol (Wireless Fidelity). WECA (Wireless Ethernet Compatibility Alliance) is
the organization behind Wi-Fi that certifies products meeting the 802.11b
specification through compatibility testing. (ww.wirelessethernet.org)
3.2.1.2.
Bluetooth
To have a wireless network which has a more localized purview, i.e., the personal area
[47], IEEE 802 Executive Committee started another working group to create a new
wireless personal area network (WPAN) in March 1999. This new working group is
IEEE 802.15 [56]. In the process of creating a standard for WPAN, the IEEE 802.11
called for proposals. By July 1999, the only respondent was the Bluetooth Special
Interest Group [57]. Due to conflicting interests between IEEE and Bluetooth group
members, Bluetooth has not yet become a standard for WPAN. However, it is the most
widely accepted proposal for WPAN.
The aim of Bluetooth is to enable design of low power, small-sized, and low-cost
radios that can be embedded in the existing portable devices. The multiple access of
Bluetooth is based on frequency hopping (FH) code division multiple access (CDMA).
The reason of not using TDMA in Bluetooth is to avoid timing issues [46], while that of
not using direct sequence (DS) CDMA is to avoid issues such as the coordinated power
control and common timing references. The Bluetooth network is a scatter ad-hoc
network in which multiple piconets exist, as shown in Figure 17. These piconets may
overlap or be disjoint. In each piconet, there is a master and multiple slaves. The master
controls the FH channels and hopping sequences, while slaves access network via the
master.
54
Figure 17. Scatter ad-hoc network of Bluetooth
Bluetooth network works in 2.45 GHZ ISM band. Both isochronous and
asynchronous services are supported by a Bluetooth network. For each unit, the
transmission rate is less than 1 Mbps.
The MAC protocol of Bluetooth is based on FH-CDMA/TDD and the piconet
architecture. A master is associated with a piconet which is identified by hop sequence
and system clock of the master. The master controls medium access so that only
communications between master and slaves are possible. The medium access is based on
the following scheme:

Polling-based MAC within a piconet. In a piconet, the master polls slaves slot by slot.
When a slave is polled, it starts transmission. The polling can be done implicitly when
the master has information to send. Otherwise, the polling has to be done explicitly
via a short poll packet. Due to polling-based access, the transmissions of slaves are
contention-free.

ALOHA-based MAC to avoid interference between piconets. Independent piconets
may interference when they occasionally use the same hop carrier. A type of ALOHA
is used to avoid this problem. The master transmits information without checking a
clear carrier. If the information is received in-correctly, it is re-transmitted at the next
transmission opportunity. Due to the short dwell time of FH channel, collision
avoidance scheme cannot be used.
55
Bluetooth is not QoS-oriented, so it cannot support multimedia applications.
Moreover, the intra-piconet scheduling and inter-piconet routing schemes need to be
developed. Also, the procedures of setting up connections are complex.
3.2.1.3.
HomeRF and SWAP
Networking in the home is required to extend the reach of PC and Internet throughout the
home and yard [48]. The Home RF Working Group was thus formed in early 1997 to
enable inter-operable wireless voice and data networking within the home at consumer
price points. A SWAP has been created by HomeRF group and is now being finalized.
In SWAP, the home network consists of two types of terminals or networking devices:
isochronous clients and asynchronous peer-to-peer devices, as shown in Figure 18. Both
of them can be connected to a main home PC. The isochronous clients are connected to
the main home PC via the HomeRF control point, while the asynchronous devices are
connected to main home PC via an Internet gateway.
Figure 18. Home networking based on HomeRF
In the HomeRF, the isochronous clients are based on TDMA, but the
asynchronous devices are based on CSMA. Thus, the MAC protocol of SWAP should
consider the hybrid of the two different systems. The frame structure of the hybrid MAC
protocol is shown in Figure 19. A superframe consists of five phases. The hop is used to
switch the hopping frequency, while the beacon maintains network synchronization,
controls the format of the frame, and manages when each terminal should transmit and
56
receive data. The contention free period (CFP) 1 and CFP 2 are based on TDMA/TDD,
while the contention period is managed according to the CSMA/CA access mechanism. It
should be noted that TDMA/TDD of CFP 1 and CFP 2 is different from the classical
TDMA/TDD structure. In CFP1 and CFP2, uplink and downlink are changed
alternatively on the slot basis. Service slot is used to send connection requests. Since the
SWAP is based on frequency hoping techniques, the frame length is equal to the duration
of a hop period.
Figure 19. The frame structure of SWAP
The operation procedures of the MAC protocol for SWAP are as follows:

Isochronous services. For each node that wants to transmit the isochronous services
such as voice data, it first sends a request to the connection point (CP), i.e., the
control point in Figure 18, via the service slot. In the beacon period of the next frame,
the assignment is sent back to the node. If it is allowed to transmit packets, it is
assigned a pair of uplink and downlink slots in CFP 2. Otherwise, the node should
send the request next time. In the CFP 2, a node which assigned a time slot can
transmit packets to the CP via the uplink slot and receive packet from the CP via the
downlink slot. Piggyback information is also transmitted in the header of each packet
to acknowledge whether packets sent in the last frame have been successfully. If
errors occur, retransmission is required, and thus a pair of uplink and downlink slots
for retransmission is assigned in the CFP 1. It should be noted that retransmission can
be performed for only one time.

Asynchronous services. The asynchronous services such as computer data access the
channel according to the CSMA/CA mechanism. In this working period, the CP is not
required and the network is of ad-hoc type. In order to avoid the hidden node issue,
the RTS/CTS also needs to be included into the CSMA/CA.
The main contribution of the SWAP protocol is to combine the TDMA based
MAC and CSMA/CA protocol. By this way, heterogeneous traffic can be supported.
Also, high system utilization can be achieved. Another advantage of SWAP is that it uses
retransmission for isochronous traffic. Low packet loss ratio of real time services can be
achieved by the fast MAC retransmission without using complicated error control
scheme. However, the TDMA based MAC in SWAP is still weak. For example, multi-
57
slot allocation is not proposed and the resource allocation algorithm to guarantee the QoS
is ignored. Moreover, retransmission of asynchronous traffic or other error control
schemes need to be developed.
3.2.1.4.
BRAN Project
ETSI has established a standardization project for Broadband Radio Access Networks
(BRAN) in Spring 1997. ETSI BRAN is the successor of the former Sub-Technical
Committee RES10 which developed the HIPERLAN/1 specifications.
The project prepares standards for equipment providing broadband (25 Mbps or
more) wireless access to wire-based networks in both private and public environments,
operating in either licensed or license exempt spectrum. These systems address both
business and residential applications. Fixed wireless access systems are intended as high
performance, quick to set up, competitive alternatives for wire-based access systems.
The specifications address the physical (PHY) layer as well as the data link
control (DLC) layer (with medium access and logical data link control sublayers as
appropriate). Interworking specifications that allow broadband radio systems to interface
to existing wired networks, notably those based on ATM, TCP/IP protocol suites and
UMTS, are or will be developed.
ETSI BRAN currently produces specifications for three major Standard Areas:

HIPERLAN/2, a mobile broadband short-range access network

HIPERACCESS, a fixed wireless broadband access network

HIPERMAN, a fixed wireless access network which operates below 11 GHz
3.2.1.5.
HiperLAN/2
There was an opposite WLAN standard, called HiperLAN/1, which was finalized by
ETSI. It works in dedicated bandwidth of 5.1-5.2 GHZ. The MAC protocol of
HiperLAN/1 is similar to CSMA/CA, so no real time service can be supported. In order
to enhance the performance of WLANs in the sense of supporting higher speed and
multimedia applications, ETSI proposed another standard, called HiperLAN/2, which is
the first WLAN standard that is based on orthogonal frequency division multiplexing
(OFDM) technology. The transmission rate of HiperLAN/2 can be up to 54 Mbps in the
physical layer and up to 32 Mbps in the network layer. HiperLAN/2 works in the 5.4-5.7
GHZ frequency band.
HiperLAN/2 network is an infrastructure-based, where services are connectionoriented. The access point (AP) in HiperLAN/2 acts like a base station, and controls the
medium access, handover, and interconnecting to other networks [50].
The frame structure of HiperLAN/2 is dynamic TDMA/TDD, which is shown in
Figure 20.
58
Figure 20. The frame structure of HiperLAN/2
Each MAC frame consists of several control channels such as broadcast channel
(BCH), frame control channel (FCH), random access channel (RCH), access feedback
channel (ACH), and the downlink and uplink transmission phases. The functions of these
control channels are described as follows:

BCH. Control information is sent via this channel. The information includes
transmission power, starting points and length of other channels, and identifiers of
AP.

FCH. This channel conveys resource allocation information.

RCH. It is used by mobile terminals to request resources in the downlink and uplink
transmission phases.

ACH. It conveys the feedback information on the access attempts in the previous
RCH.
The MAC protocol of HiperLAN/2 is operated according to the following
procedure:

Connection request. Mobile terminals send connection requests in the RCH, and get
feedback about access attempts in the ACH. In this process, random access protocol
is used, and collision resolution scheme is needed.

Admission control. To determine whether a connection request can be accepted, an
admission control scheme must be used. Since HiperLAN/2 is a type of wireless LAN
network, the admission control schemes for ATM networks can be used. However,
certain modifications are necessary in order to make them applicable to the wireless
environments.

Broadcast resource allocation via FCH. The information of allocated time slots for
each connection is sent back to mobile terminals via FCH in a broadcast way.

Data transmission. When a mobile terminal is allocated time slots, the packets from
high layers are segmented into ATM cells, and transmitted in the assigned time slots.
HiperLAN/2 holds the following features [50]:

High data transmission rate is possible

Network is ATM-based and connection-oriented, so QoS of multimedia traffic is
supported

Automatic frequency selection is performed at the AP, so no frequency planning is
required
59

Power saving management is embedded in the protocol

Mobility is supported

Flexible architecture to support different network environments

Plug-and-play radio network

Manageable and scalable bandwidth
However, HiperLAN/2 has several problems such as high protocol overhead for
IP traffic, low-throughput for bursty and delay-insensitive traffic, because it is based on
wireless ATM technology.
Table VII below summarizes the characteristics of 802.11, 802.11b, 802.11a, and
HiperLAN/2 [93].
Table VII. Comparison between 802.11 and HiperLAN/2
Characteristic
Spectrum
Max Physical Rate
Max data rate layer 3
Medium access
Connectivity
Multicast
QoS support
Frequency selection
Conn.-less
Yes
No
FH/DSSS
Authentication
No
No
No
Encryption
Handover support
Fixed network support
40bit RC4
No
Ethernet
40bit RC4
No
Ethernet
40bit RC4
No
Ethernet
802.11MIB 802.11MIB
No
No
802.11MIB
No
Management
Radio link quality
control
802.11
2.4GHz
2Mb/s
1.2Mb/s
802.11b
802.11a
2.4GHz
5GHz
11Mb/s
54Mb/s
5Mb/s
32Mb/s
CSMA/MA
Conn.-less
Conn.-less
Yes
Yes
No
No
DSSS
Single carrier
HiperLAN/2
5GHz
32Mb/s
32Mb/s
TDMA/TDD
Conn.-oriented
Yes
Yes
Single carrier
with Dynamic
Frequency
Selection
NAI/IEEE
address/X.509
DES, 3DES
No
Ethernet, IP,
ATM UMTS,
FireWire, PPP
HiperLAN/2MIB
Link adaptation
HiperLAN/2 enables QoS, automatically frequency allocation, power saving and
security support, and is network independent. However, as most major vendors produce
their wireless LAN products according to IEEE 802.11 standard, IEEE 802.11 has
become the practical standard for most markets. Market drives plays an important role in
the competition between the two different standards.
60
Currently, network operators intend to deploy 802.11x wireless LAN, especially
802.11b, instead of HiperLAN networks. Such a situation is caused by both technical and
non-technical factors.
In terms of non-technical factors, many big manufactures and IEEE committee
support 802.11 and try to have a global standard for wireless LAN. When they developed
802.11b techniques, they just pushed it to get the level of performance that was enough as
needed. Thus, not so much engineering effort is required to create products. However,
HiperLAN standard is too good to be true [104]. ETSI HiperLAn group tried to make the
technique advanced. However, it turned out to be too advanced and too late. Finally, most
of the WLAN manufactures tend to back IEEE 802.11 instead of HiperLAN. For
example, Intel clearly pointed out that they like to support IEEE 802.11 and Bluetooth in
their chip design, but they are not willing to back HiperLAN.
In addition to non-technical factors, there do exist non-technical factors.
1. ATM versus IP. HiperLAN/2 is a wireless ATM technique. Although it is able
to carry the IP traffic over ATM, most of the industrial companies do not like
such a design, because IP seems to be dominant network solution in the world
market.
2. Network Infrastructure. IEEE 802.11x supports both Ad-hoc and
Client/Server network architecture. However, HiperLAN only supports the
client/server architecture. Thus, IEEE 802.11 WLAN is much more flexible in
industrial application.
3. Frequency Band. IEEE 802.11b works in ISM 2.4 GHz band. Such a band is
globally license-free. Thus, IEEE 802.11b was quickly accepted by many
manufactures, vendors, and companies. However, HiperLAN works in 5-GHz
band. Such a frequency band has not been assigned to be free to use in many
countries. IEEE 802.11a share the same problem with HiperLAN. Athough in
the future, global license-free 5GHz frequency band believes to be available,
the application of HiperLAN is much later than 802.11b.
4. Complexity and Price. HiperLAN is too advanced, which results in the
complexity in implementation. It is generally expensive to implement
HiperLAN protocol in a chip set of a PC, PDA, and other terminals. However,
implementing IEEE 802.11x in a chip set is simpler, and thus low cost WLAN
can be easily provided to different type of WLAN users.
However, although HiperLAN/1 is not an interest to any network operators,
HiperLAN/2 is still in progress. Due to its high speed and QoS guarantees, it will be a
strong competitor with IEEE 802.11a WLAN in the world of 5GHz frequency band.
Which will be the winner is not obvious at the moment.
61
3.2.2.
Current Use of WLAN and Industry Practices
Because of the mobility, flexibility and low cost of WLAN, it has numerous practices in
many areas such as home, enterprises and public accesses.

Home wireless networks. WLANs are an ideal, no-hassle, no-wires alternative for
networking computers and Internet appliances at home. They can be installed easily,
expanded quickly and reduce the cost of setting up a wired network.

Enterprise wireless networks. WLAN save time and money for enterprises. They also
enable dynamic movements, scalability, and easy implementation. And they are
easily to be integrated to an existing LAN. Wireless Networking is used to connect
disparate networks in different locations. Building-Building or LAN-LAN wireless
networks are being used by many industries serving diverse applications. Point-topoint and point-multi-point connections allow users in different locations the
opportunity to access the Internet, share files, and access network resources without
wires.

Public access. Wireless Internet service providers (WISPs) now offer public WLAN
access for at various locations such as airports, airline clubs, conference centers,
hotels, restaurants, and cafes. Using a laptop or PDA, users can access the wireless
Internet, or log into a company intranet through a VPN (virtual private network)
client. Public access WLANs do not worry to search for a data port. Access speed that
is 50-200 times faster than dial-up, thus it is practical to make large file transfer. And
the service is affordable with flexible payment options and no long distance charges.
Here are more typical examples of current WLAN practices:

Hospitals. Hand-held devices and portable computers are able to deliver patient
information to doctors and nurses in real time, providing information that can save
lives. In addition, administrative productivity is bolstered through the elimination of
redundant paperwork.

Warehouses. Workers use wireless devices to deliver instant updates regarding
supplies and inventories to centralized databases providing more accurate information
to the management team. Bar code readers with wireless, data links are used to enter
the locations and to identify inventory, improving operational efficiency and reducing
costs associated with physical inventory counts.

Consulting and audit teams. Small work groups can quickly establish private and
integrated networks as they move from site to site.

Dynamic environments, ad agencies, etc. The cost of LAN ownership can be reduced
significantly in dynamic environments with multiple additions and moves.

Universities. Many universities have implemented campus-wide WLAN technologies
as students become increasingly PC dependent. New York University, for instance,
provides each entering freshman with a laptop computer as part of his/her tuition. By
implementing WLANs, colleges like NYU can provide accessible data to students,
both as they travel around campus and when they are unable to access a wireline
connection.
62

Historic buildings, older buildings. Many government and otherwise historic
buildings have regulations against changing the building infrastructure, denying the
possibility of pulling new wiring through the walls. WLANs are, in these
circumstances, the only possible form of data networking. Trade Shows-WLANs
provide quick and flexible setup capabilities that allow trade show personnel and
convention centers to constantly change the network structure from one show to the
next.

Meeting rooms. Real-time information allows management to make more informed
decisions during meetings.

Retail stores. WLANs enable frequent network reconfiguration.

Restaurants and car rental agencies. Real-time information transfer enables superior
customer service. Examples include Avis and Hertz.

Data backup. Mission-critical applications can be implemented with a wireless
backup in the case of malfunctions in the wired infrastructure.
3.2.3.
Working Frequency, Typical Bandwidth, and Propagation
Footprints of WLAN
The technologies of typical WLANs have been described in Section 3.2. In this
subsection, we summarize these techniques in terms of working frequencies, typical
bandwidth, and the propagation footprints.
Since IEEE 802.11 working group has proposed several physical layer
specifications, the working frequency, available bandwidth, and propagation
characteristics are dependent on the physical working modes, as listed in Table VIII.
Table VIII. Different Physical layers specified by IEEE 802.11
Operating Modes
Frequency Band
Transmission Rate
Radio based,
legacy DSSS
Infrared-light
based, legacy DSSS
Complementary
code keying (802.11b)
OFDM (802.11a)
2.4 GHZ ISM band
2.4 GHZ ISM band
1 Mbps with BPSK
2 Mbps with QPSK
1 Mbps with BPSK
2 Mbps with QPSK
11 Mbps/5.5 Mbps
5 GHZ
6-54 Mbps
Infrared-light
Propagation
Footprints
cellular or ad-hoc
cellular or ad-hoc
LoS
cellular or ad-hoc
cellular or ad-hoc
In Table VIII, the cellular propagation footprint means that the 802.11 network
works in an infrastructure based architecture. In such a scenario, mobile terminals
communicate with an AP. Thus, the mobile terminals controlled by an AP lie in the cell
which is covered by this AP. Handoff is required when a mobile terminal cross cells.
When the 802.11 network works in ad-hoc mode, mobile terminals communicate peer-topeer, so there is not a fixed pattern of the propagation footprints.
In a Bluetooth network, FH-CDMA/TDD is used, so the core physical layer
technique is FH-CDMA. The working frequency of HomeRF is in 2.45 ISM band. Since
63
a piconet uses one FH carrier, each Bluetooth unit cannot support the transmission rate of
up to 1 Mbps. Due to the scatter piconet concept used in Bluetooth, the propagation
footprint is non-regular. However, in each FH period, there exists an irregular cell that is
controlled and covered by the master. In such an irregular cell, all slaves must
communicate with the master.
HomeRF network works in the 2.4 GHZ ISM band. The physical layer is based on
FH, and modulation is 2-FSK or 4-FSK. HomeRF control point (CP) has low transmitting
power and can be implemented on a single chip. It has native support of Internet access,
and voice telephony access is provided through PSTN. The maximum transmission rate
of HomeRF non-real time services is up to 1 Mbps. When devices communicate with
each other peer-to-peer, no fixed propagation pattern exist. On the other hand, if the
devices are controlled by the CP, the network has a cellular structure, in which all devices
communicate through the CP.
The physical layer of HiperLAN/2 network is based on OFDM technique, which
enables that the physical layer transmission rate can be as high as 54 Mbps. In the
network layer, the transmission rate can be also up to 32 Mbps. HiperLAN/2 works in
5.4-5.7 GHZ frequency band, which is dedicated in Europe. In HiperLAN/2, the AP acts
like a base station. So all mobile terminals communicating with such a base station
actually work in the cell covered by the AP. When mobile terminals move from one cell
to another cell, handoff procedure is invoked.
As described previously, almost all the WLANs work in the frequency band
around either 2.4 GHZ or 5.3 GHZ. It should be noted that the radio wave propagation
introduce a path loss penalty of 6.9 dB going from 2.4 GHZ to 5.3 GHZ [54]. This means
that, for WLANs working in 5.3 GHZ frequency band, almost five times of RF power is
required to cover the same distance as WLANs working in 2.4 GHZ frequency band. For
the same reason, the RF propagation through barriers is poorer when 5.3 GHZ frequency
is used.
3.2.4.
Interference to WLANs
Interference in wireless systems is always an important issue because users near the local
vicinity occupy the same bandwidth and cause co-channel interference. For WLANs, in
addition to co-channel interference, other types of interference exist because generally
WLANs work in the unlicensed ISM frequency band. In the same ISM frequency band,
one type of WLAN may coexist with other types of WLANs or devices such as
microwave oven and ultrasonic equipment. Thus, the interference to WLANs comes from
the following major sources:

Co-channel interference. Co-channel interference arises due to uncoordinated users
occupying the same bandwidth within or near local vicinity [60]. In a WLAN
environment, since the transmission distance is short, the time dispersion from the
propagation channel is low [60]. Thus, co-channel interference becomes an important
factor of determining the SINR of the received signal. According to the ShannonHartley Law [61], the normalized capacity  can be derived as
 = log2(1 + S/(I+N))
64
(1)
where S is the received interference power, I is the received co-channel interference
power, and N is the noise power. Thus, from this equation, we know that if cochannel interference arises, the normalized capacity is reduced. This causes the
degradation of network performance of WLAN. For example, the throughput and
transmission rate are reduced if a fixed BER is required. In other words, if a fixed
throughput is required, the BER will be increased. There are two approaches for
reducing the effect of co-channel interference. One is to use the MAC protocol to
determine the level of co-channel interference and select an appropriate channel for
each user. Thus, for each channel, during a certain period, only one user transmits
signals and other users in the immediate vicinity stop transmitting. The other
approach is to use co-channel interference rejection technique in the physical layer.

Interference from non-WLAN devices in the same frequency band. Most of WLANs
work in the ISM band, i.e., the frequency band of 900 MHZ, 2.4 GHZ, and 5 GHZ,
where have already been used by other ISM devices such as microwave ovens,
medical diathermy, and ultrasonic equipment. It is known that such ISM band
interference exhibits impulsive characteristics and seriously degrades the performance
of WLANs [62]. Thus, new techniques are necessary to reduce the interference or
make the WLANs be more robust to operate in the presence of ISM interference. For
example, in a new multicode transmission technique is proposed for DSSS system so
that good performance can still be achieved in the presence of ISM interference.
Reducing interference in the MAC layer is possible, but it must be much more
difficult than in the physical layer. The reason is that the other ISM devices such as
microwave ovens are not network components and cannot communicate with
WLANs.

Interference between different WLANs in the same frequency band. It is quite possible
that different types of WLANs use the same ISM band. When they are deployed in
the near vicinity, interference to each other will seriously degrade the performance of
WLANs. Thus, coexistence of WLANs of the same ISM band is a challenging
research topic. For example, in the 2.4 GHZ ISM band, the coexistence of Bluetooth
and 802.11b has been widely researched.
In the 5 GHZ ISM band, the coexistence of HiperLAN/2 and IEEE 802.11a is also
an issue. To reduce the interference between WLANs in the same ISM band, many
schemes have been proposed [54], [63], [64], and [65]. In general, the coexistence of
WLANs can be enabled in the following ways [55], [66], [67]:

Regulatory and standards. Rules can be used to change the operation frequency
segment of a channel so that the interference can be reduced. This has been proposed
by FCC for Bluetooth. For example, a piconet in the Bluetooth might hop one
segment of the band instead of the whole 2.4 GHZ ISM band. In addition to rules,
standard and industry bodies should work together to make a rapid progress toward
providing a suite of coexistence tools.

Usage and practices. When one WLAN is working, others are banned. In such a way,
interference can be greatly reduced. However, this is not practical. Thus, modal
operation of WLANs can be a good alternative. However, when WLAN devices grow
65
to a high density, this approach is not feasible either. Thus, this type of methods
cannot really solve the interference issues between WLANs.

Technical approaches. Such approaches are implemented in different layers such as
driver layer, MAC layer, and physical layer. In the driver layer, software above the
MAC layer can be installed for different types of WLANs. Thus, software switch
from one WLAN to another WLAN is required. However, the approach in this layer
does not work when more than one WLAN are working in the same time period.
Thus, the approach in the MAC layer is more attractive. To propose schemes in the
MAC to reduce the interference between WLANs is still an on-going research topic.
In the physical layer, signal processing techniques and anti-jamming schemes can be
used to reduce the interference and keep the performance of WLANs. However,
physical layer techniques tend to directly affect system costs more than the MAC
layer techniques, because the MAC layer comprise digital hardware and software, and
techniques employed here tend to be relatively inexpensive to implement. Therefore,
the techniques of physical layer and MAC layer need to be balanced.
3.2.5.
Environmental Issues
Effect of wireless technology on health is one of the most discussed and to be concerned
issue, as the devices emit radio frequency electromagnetic energy. The radiation used by
this technology, fall well within the limits of safety guidelines (both in terms of
frequency content and power level) specified by Radio Frequency Safety Standards and
Recommendations. Hence it has been proved that WLAN is safe for health.
Widely accepted and recognized standard bodies for health regulations are
ANSI/IEEE, NCRP, NRPB, and IRPA/INIRC. The safety limits specified by these bodies
are very much the same, with little differences. ANSI/IEEE Standard (ANSI/IEEE C95.11992) specifies safety levels with respect to Human Exposure to Radio Frequency
Electromagnetic Fields, from 3 KHz to 300GHz. Radiation in this frequency range is
non-ionizing (as they do not have enough energy to break the chemical bonds of genetic
material of body cells). The limit set by ANSI/IEEE C95.1-1992, for radio power in the
above frequency range is in terms of, whole-body averaged energy absorption rate (i.e.
Specific Absorption Rate or SAR) and it is 0.4W/Kg of the body tissue in environments
designated either occupational or "controlled" and 0.08W/Kg in environments designated
either public or "uncontrolled".
WLAN Technology use frequency bands around 2.4GHz and 5GHz. Hence
radiation is non-ionizing. Moreover, manufactures of WLAN products are designing their
products to operate within the power limit set by the Safety Standards. In fact most of the
products have power specifications which is much below the specified limits (typically in
the range of 35mW [68]). Hence the technology is safe for health.
Apart from the fact that it is safe to use, there are many more added advantages,
inherited to WLAN Technology. Some of these are absence of wire in network (which
makes it convenient and quick for network setup, trouble shooting, relocation and
expansion etc). Also WLAN looks much better and cleaner compared to the wired one.
User mobility, reduced-cost of ownership, real-time-access to information, and positive
66
impact on user psychology are the added differentiations that WLAN has over Wired
LAN. All these features make WLAN a more friendly technology, for its user.
3.2.6.
Major Suppliers of the WLAN Products
There are three kinds of product in the WLAN: access point, LAN adapters and LAN
bridges. In Table IX, major suppliers of access points are compared. In Table X, major
suppliers of LAN adapters are compared. In Table XI, major suppliers of LAN bridges
are compared.
Some operators such as Nokia use GSM SIM card for authenticating the user.
Each SIM card stores a standard GSM International Mobile Subscriber Identity (IMSI)
code that identifies the user and the home operator. In Wireless LAN, the SIM is
integrated within Wireless LAN Card fitted to the user's laptop. Typically, this SIM is
used for Wireless LAN access, but it can also be used as a separate SIM card to make and
receive GSM calls while using the Wireless LAN. Using SIM authentication also
provides full GSM international roaming capability with GSM roaming partners.
67
Table IX. Comparison of access point products of major suppliers
Major
suppliers
Agere
Avaya
Nokia
Nortel
Intel
Intel
Siemens
3Com
Fujitsu
Compaq
Agere
Apple
IBM
Cisco
Products
AP-1000
I/700022270
A032
e-mobility
DSSS AP
DR4000E02
PRO/Wireless
2011B
PRO/Wireless
5000
I-GATE 11M
Access Point
6000
MBH8MB01
WL510
AP-1000
AirPort
AP500
Aironet 350
Series
Operating
Frequency
2.4GHz
2.4GHz
2.4GHz
Standard
Throughput
WEP
Encryption
64- and 128bit
-
802.11b
802.11b
802.11b
11Mbps
11Mbps
11Mbps
2.4GHz
802.11b
11Mbps
2.4GHz
802.11b
11Mbps
5.2 GHz
802. 11b
54 Mbps
2.4GHz
2.4GHz
802.11b
802.11b
11Mbps
11Mbps
64- and 128bit
64- and 128bit
11Mbps
64-bit
2.4GHz
2.4GHz
2.4GHz
2.4GHz
2.4GHz
2.4GHz
Bluetooth
802.11b
802.11b
802.11b
802.11b
802.11b
732.2kbps
11Mbps
11Mbps
11Mbps
11Mbps
11Mbps
128bit
128bit
-
Table X. Comparison of LAN adapter products of major suppliers
Major
suppliers
Intel
Intel
Compaq
Agere
Apple
Cisco
Products
PRO/Wireless
2011B LAN
PC Card
PRO/Wireless
5000 LAN
PCI Adapter
WL110
ORiNOCO
PC Card
Airport Client
Card
Aironet® 350
Series
Operating
Frequency
2.4GHz
Standard
Throughput
Range
802.11b
11Mbps
-
5.2GHz
802.11a
54Mbps
100 feet
2.4GHz
2.4GHz
802.11b
802.11b
11Mbps
11Mbps
-
2.4GHz
802.11b
11Mbps
-
2.4GHz
802.11b
11Mbps
-
68
Table XI. Comparison of LAN bridge products of major suppliers
Major
suppliers
Intel
Compaq
Agere
Agere
Cisco
3.2.7.
Products
Wireless
Gateway
WL310
RG-1100
Broadband
Gateway
ORiNOCO
PC Card
Aironet®
350 Series
Wireless
Bridge
Operating
Frequency
2.4GHz
Standard
Throughput
Range
802.11b
11Mbps
-
2.4GHz
2.4GHz
802.11b
802.11b
11Mbps
11Mbps
160m(525feet)
550m(1750ft)
2.4GHz
802.11b
11Mbps
-
2.4GHz
802.11b
11Mbps
25 miles (40.2
km)
Radio Link Quality Control
Radio link in wireless domain is the path or combination of paths from the transmitter to
the receiver. The radio link governs the communication quality in terms of BER for a
specific transmitter power level or in other words, given the BER specification
determines the required transmitter power. In case of WLAN this is very critical for
system performance. As there exist a limit on maximum amount of power which can be
transmitted as per FCC regulation, for different standards. The radio link quality along
with the transmitter power determines the range of communication for a specific
communication performance in terms BER. We will first discuss important system
parameters and variables required for this analysis of indoor WLAN range, then talk
about link budget, taking into consideration, one suitable path loss model into
consideration.
3.2.7.1.
System Parameters
The indoor coverage range depends on maximum allowable transmitted power
and nominal sensitivity. Such specifications are as per IEEE 802.11a and IEEE 802.11b
standards. Table XII compares the specific parameters that determine the indoor coverage
range as per IEEE 802.11a and IEEE 802.11b standards in USA and Europe. It is to be
noted that the Packet Error Rate (PER) of both these standards are same.
69
Table XII. System parameters
IEEE 802.11a
IEEE 802.11b
3.2.7.2.
Transmit
Power
Transmit
Gain
Receive
Gain
Receiver Sensitivity
USA
23dBm
6dBi
0dBi
-82dBm to –65 dBm
Europe
23dBm
0dBi
0dBi
-82dBm to –65dBm
USA
30dBm
0dBi
0dBi
-70dBm
Europe
20dBm
0dBi
0Dbi
-76dBm
Path Loss Model for Indoor WLAN
The indoor radio channel model differs from that of traditional outdoor wireless models
because of two main reasons: small distance of coverage and large variation in
environment for small within small distance. From various experiments it has been
observed that path loss in indoor environments are strongly influenced by building
features like building layout, material etc. Indoor propagation is dominated by reflection,
diffraction, and scattering. Many different types of models are proposed for such signal
propagation. When both the transmitter and receiver are on the same floor the
propagation loss can be modeled as the Keenan-Motley or Devasirvatham model. This
model predicts the path loss as the summation of free space path loss plus a factor which
varies linearly with range. The average signal path loss model can be represented by the
following equation [105]:
PL(d , f )[ Db]  PLFS (d , f )  a.d
(2)
where d is the distance, f is the frequency of operation, PLFS is the free space path loss,
and a is the linear attenuation coefficient (typical value of 0.47 [dB/m] for an office
environment).
3.2.7.3.
Link Budget for Indoor WLAN
The indoor coverage range is calculated using the link budget formula according to the
parameters specified by standards (given in previous table). Using the formula we can
given the transmitted power, the coverage distance d can be calculated. The received
power is related to transmitted power, antenna gain and signal path loss by the following
equation:
Pr[dB]=Pt[dB] + Gt[dB]-PL(d,f) [dB] –Gr[dB]
(3)
where,
Pr[dB] is the minimum received power to meet PER/FER (receiver sensitivity),
Pt[dB] is the maximum allowed transmit power,
Gt[dB] is the transmit antenna gain,
Gr[dB] is the receiver antenna gain,
PL(d,f) [dB] is the indoor signal path loss given by Equation 2.
Using the above equation for a particular standard we can fine the in-building
coverage area. In the above case we have assumed one channel model (path loss model).
70
But the link budget equation is valid for any path loss model. Using the above
propagation model the range of indoor WLAN is found to be around 47.4 m at 5 Ghz at
11 Mbps as per IEEE-802.11a (Europe) and 57 m for (USA).
3.3.
WLAN Types and Their Characteristics
WLANs are really diverse, and it is impossible to have a single standard for them.
However, they can be categorized into several types according to certain criteria. For
example, we can categorize WLANs according to working groups or standardization
committee. We can also classify WLANs according to their different frequency bands. In
this subsection, we use the multiple access schemes as a criterion to categorize and
compare WLANs. Thus, WLANs can be categorized into the following types:

CSMA/CA based WLAN. Due to simplicity of CSMA/CA, many WLANs are based
on this technique. For example, IEEE 802.11 belongs to this type. Since CSMA/CA
has hidden node and exposed node problems, some mechanisms such as request to
send (RTS) and clear to send (CTS) are needed to enhance its performance. The basic
network topology of CSMA/CA-based WLAN is ad-hoc. To provide network access
to backbone, an AP is required. Considering that CSMA/CA is weak in QoS
guarantees of real time services, so AP also helps to support the real time services.
However, how to really deliver QoS guarantees in this type of WLANs is still being
researched.

ALOHA- and Polling-based WLAN. This type of WLAN is especially used in WPAN
because of its simplicity. Also, due to the weakness of ALOHA in the sense of QoS
guarantees, this type of WLAN is not applicable to wider areas. Bluetooth and IEEE
802.15 WPAN belong to this type. The typical network topology of this type of
WLANs is ad-hoc. To control the medium access and provide access to backbone, a
master is generally used. The master can be dynamically selected in order to have
more flexibility, which has been done in Bluetooth. This type WLAN has low
transmission rate, and is weak in QoS guarantees. Multimedia services cannot be
supported by this type of WLANs.

TDMA or CDMA based WLAN. Compared to CSMA, TDMA and CDMA are more
flexible in resource management. The resources such as time slots or codes of a
network can be allocated to a user by a reservation scheme. Thus, TDMA or CDMA
based WLANs are becoming more and more attractive to developers and network
customers. However, because of the higher complexity existing in TDMA and
CDMA techniques, the cost of developing, manufacturing, and deploying such
WLANs is more expensive. As TDMA and CDMA techniques quickly develop,
especially in the physical layer, their cost will become so low that it can be acceptable
to local area environments and users. Thus, TDMA or CDMA based WLANs are a
promising option to provide next generation WLANs. Currently, most of the
proposals in IEEE 802.16 working group are based on TDMA or CDMA techniques.
In ETSI, HiperLAN/2 is also based on the TDMA technology. Because of using
TDMA as the multiple access scheme, resources in HiperLAN/2 can be reserved and
a virtual connection can be established as in an ATM network. In such a way, the
QoS of multimedia traffic can be guaranteed.
71

Hybrid WLAN. TDMA or CDMA can be used in combination with other multiple
access schemes such as CSMA or ALOHA. For example, in HomeRF, the MAC
protocol is based on a hybrid frame structure, i.e., the whole frame consists of the
TDMA phase and the CSMA phase. The delay-insensitive traffic can be sent in the
CSMA phase, while real time traffic such as voice is transmitted in the TDMA phase.
The hybrid WLAN has the advantage of flexibility. It provides the low access delay
for data traffic, so that users can feel that the network is always on, which is the
feature of Internet. Although the access time of real time traffic is generally larger
due to the process of resource reservation, the QoS is guaranteed. Unfortunately, the
TDMA-based MAC part is still very simple. Actually the real time service is
supported via the PSTN. Thus, the current HomeRF protocol only supports single slot
allocation to isochronous services, and it cannot support many types of real time
traffic. To have a powerful hybrid WLAN depends on the advances of both physical
layer and data link layer techniques.
3.4.
Main Target Market Forecast
The unexpected growth of Internet over last few years has proved the fact that
platforms/technologies that support data and resource sharing are boon for explosion in
business and added personal convenience. This provided motivation to apply the concept
of data and resource sharing to other domains of communication, which gave birth to
Wireless Networking in the LAN space. Development and penetration of WLAN
technology since its conception has further strengthened the above argument. The market
for WLAN products is increasing more than predicted, and its future is forecast to be
huge and it is going to be omni-present, starting from inside of home to offices,
educational institutes, health care centers, warehouses, hotels, airports and many more.
3.4.1.
Current Market Segments and Their Market Penetration
Though the ultimate aim of WLAN technology is to replace the wired infrastructure, at
present it is a significant compliment to what currently exists. Corporate, educational
institutes, health care centers, manufacturing companies etc are installing WLAN systems
to increase both user and IT team productivity. The present market for WLAN
Technology includes but not limited to the following sectors:

Corporate. Many companies are going for WLAN alternative, as it is providing a
common working platform of shared files and shared resources. It has already proven
(through market study) that WLAN is more convenient, productive, user friendly and
cost effective for corporate.

Education. In educational institutes WLAN is expanding its presence with
classrooms, laboratories, libraries, student center, sport complexes, getting connected
to its backbone network through wireless links. The advantages provided by WLAN
are more in-class-productivity, low-cost and wide-coverage network setup,
convenient access to institute's network from anywhere inside the campus (which
makes it possible for both faculty and students to setup group study/discussion
through desktops/laptops even though members are physically far apart). Institutes
72
are also saving lots of money by buying fewer computers as the same ones can be
used alternatively in different classes and laboratories at different times.

Healthcare. To take the advantages of this most sought after technology, hospitals are
centralizing their laboratories, resources through WLAN. This promising technology
has shown to meet their needs by decreasing the length of hospital stay, speeding
diagnostic and case analysis time (as doctors and nurses have access to patient's file
irrespective of their physical separation), procedural costs, documentation etc.

Manufacturing. Because of its size, frequent changes in assembly line, changing work
location, it is cost prohibitive and also not feasible to lay cables in manufacturing or
factory floors. Also in such environments, workers and management many times need
instantaneous access to accurate information to track production runs, and production
quantities in real time. WLAN is offering all these, hence its use in this sector is
growing steadily.

Warehouse. WLAN is enabling warehouse workers to input and access data in realtime using mobile devices, linked to the mainframes or servers with software
applications (like inventory collection, order fulfillment, shipping/receiving
applications etc.) running on them. This also reduces the paper work by a great extent
and has proved to be convenient both for workers and management.

Retail. Use of WLAN in retail industries (such as restaurants, military stores, grocery
stores etc) have proved to have many advantages like reduction of long lines of
customers, faster rate in getting customer checkout and totaling orders, faster rate in
receipts of goods and taking inventories. It is also very much helpful for the decision
makers in retail, as it provides them real-time information about ordering, collection,
distribution and sale of goods.
A study by Wireless LAN Association (WLANA) has the following data on WLAN
market penetration in different segments [75] (as shown in Figure 21).
Figure 21. WLAN market share of different segments
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3.4.2.
A Forecast of the Target Markets and Estimated Market Size
The growth, user acceptance, user satisfaction of WLAN technology, since its presence in
the market, strongly claims that, this is going to be "The Technology" of the future.
Steady developments of WLAN technology are supporting two major causes: decrease of
product price and increase of network speed, which are the reasons behind continuous
increase in shipments of WLAN devices. Apart from current sectors, more and more new
markets are opening up for this technology. Some of these are shipping and receiving
area, distribution center, cafeteria, home, train, bus, airport, sport complexes, trade
shows, coffee shops, etc. It is also under consideration, to make WLAN as a viable option
to connect the developing nations to the developed part of the world, making the concept
"Global Village" a reality. As its products are becoming cheaper, WLAN can be set up in
different parts of these countries. These distributed networks can be connected to each
other and also to rest of the world through satellite IP Network. This has huge market
potential.
In the present market scenario Wi-Fi (IEEE802.11b) products are becoming
increasingly popular and are looked upon as the driving force for future WLAN market.
Taking into account the accelerated growth of WLAN market, several market research
groups have estimated a five-fold increase in its market by 2005. This corresponds to a
complete enterprise WLAN end-user revenue to reach about 3.2 billion dollars.
3.5.
Technology Development Prospect Analysis
Future WLAN technologies should provide faster speed, better performance, more
security and lower price. There are many areas requiring further developments:

WLAN will have higher speed. WLAN network data rates have increased from 1 to 11
Mbps for Wi-Fi known as IEEE 802.11b, referring to the 2.4-GHz. WECA(Wireless
Ethernet Compatibility Alliance) is planning to test for Wi-Fi5 for IEEE 802.11a
standard at 5-GHz. It provides up to 54Mbps and will provide greater system
capacity. The 5.7-GHz band promises to allow for the next breakthrough data rate of
100 Mbps. Future generations of products should support both the two Wi-Fi
products and make a smooth migration. IEEE 802.11g committee is trying to extend
the 2.4-GHz technology to higher speeds.

To provide high-speed multimedia communications among different broadband core
networks and mobile terminals ETSI's BRAN (Broadband Radio Access Networks)
has developed HIPERLAN/ 2 as a flexible Radio LAN standard designed to provide
high speed access (up to 54 Mbit/s at PHY layer) to 3G mobile core networks, ATM
networks and IP based networks.

WLAN needs more security guarantees. 802.11a task group is addressing the WLAN
security problems. Wired Equivalent Privacy (WEP) algorithm of 802.11 provides
WLAN security by using secret key for authentication and encryption. However, such
mechanism has a principal limitation: the standard does not define a key management
protocol for distribution of the keys. Therefore, we need a key management protocol.
74

Many new futures and applications will occur for WLAN. Many semiconductor and
product vendors are driving to new architectures and new levels of integration to
decrease the size, cost, power consumption of WLAN devices. At the same time, they
are adding new futures and applications for various market demands. Researches are
being performed to find ways to adjust 802.11 network parameters dynamically to
improve throughput. Industry also needs a standard to addresses the tracking or
management of mobile devices in its Management Information Base (MIB).

WLAN needs to improve its reliability. Reliability is also a challenge that many
organizations face with WLANs. Currently, wired LANs are more reliable than
WLANs. We need to address interference problems and enhance signal strength.

Efficient and concurrent uses of bandwidth. Wideband Orthogonal Frequency
Division Multiplexing (W-OFDM) is a transmission scheme that enables data to be
encoded on multiple high-speed radio frequencies concurrently. This allows for
greater security, increased amounts of data being sent, and is claimed to be the
industry's most efficient use of bandwidth. W-OFDM tries to solve the problem that
Bluetooth and 802.11b networks have when operating in the same frequency range. It
enables the implementation of low power multi-point RF networks that minimize
interference with adjacent networks. This reduced interference enables independent
channels to operate within the same band allowing multi-point networks and point-topoint backbone systems to be overlaid.
3.6.
Interworking/Integration with IMT-2000
The issue of interworking/integration of WLAN can be analyzed from two angles. The
first case is to establish a communication link between two devices one of which is in
WLAN and the other one being in an IMT-2000 network. The second case is when a
device in WLAN can smoothly move to IMT-2000 network and vice-versa, as shown in
Figure 23. The first issue can be solved by using the Ethernet backbone between WLAN
and IMT-2000 network by using suitable adapters in both sides, as shown in Figure 22.
The second issue is still an open problem, though there are few solutions existing. As
both technologies operate at different frequencies, the issue of seamless inter-system
movement can be made possible by using a suitable interface which will take care of the
frequency conversion and other issues while the mobile is moving from one network to
the other. Birdstep Technology, a Norwegian software vendor, together with Ericsson has
a solution which allows session transparent IP roaming for mobile users between UMTS
and WLAN.
75
Figure 22. Interoperation between WLAN and 3G
Figure 23. Inter-system movement between WLAN and 3G
Wireless ISPs can offer 2.5G/3G cellular networks and WLAN to mobile users.
Some operators currently provide those services which simultaneously support multiple
access technologies, i.e., IEEE 802.11 for high-bandwidth access in urban areas and
GPRS for wide area access in rural areas. Each technology has its advantages and
disadvantages. The 3G cellular systems are designed to carry voice, video and data
simultaneously. It can provide 2 Mbps data rates for fixed users, 144 Kbps for fastmoving mobile users (such as in vehicles), and 384 Kbps for slower moving users (such
as pedestrians). 3G cell can cover a very large area, but it works in a circuit-switched
pattern. On the other hand, WLAN provides a much higher bandwidth. And it is works in
an IP-alike pattern similar to wired Ethernet. However, WLAN operates within the local
area, and can supports only best effort services. WLAN users share the unlicensed
spectrum where few quality assurances can be guaranteed.
Currently, 3GPP is considering the interworking between WLAN and 3G
network. Such an interworking should include security, mobility, QoS , charging, and
also support different WLAN standards to interwork with 3G. More and more operators
around
the world are evaluating and integrating WLAN into their current and nextgeneration networks. Ericsson and Telenor are devising a 3G/WLAN interworking
solution, and developing standards for this integration.
76
The interworking of services could result in numerous advantages, thus it can
enable the operator to acquire more customers. However, Telenor has also identified two
possible scenarios that could undermine the 3G/WLAN interworking business. First, the
demand for WLAN services could fall away once 3G services are widely available.
Second, the stand-alone public WLANs could take off and reduce demand for both 3G
and integrated 3G/WLAN offerings.
3.7.
Service Analysis
With the development of wireless industry and wireless application, a much wider variety
of services will be available for WLAN.

Network adapter card. This is the primary function of WLAN devices provided for
PCs, notebooks, and Access Points.

Convergence for voice and data networks. The wireless LAN infrastructure can be
used for a mobile PBX handset. As voice, audio and video are shared among WLANenabled phones, MP3 players, web cameras, interactive TVs, etc, wireless
applications will move beyond traditional computer networking.

Replacement of proprietary cables. Users can connect one device to another with one
universal short-range radio link. For instance, Bluetooth radio technology built into
both the cellular telephone and the laptop would replace the cumbersome cables used
to connect among laptops, cellular telephones, printers, PDA's, desktops, fax
machines, keyboards, joysticks and virtually any other digital device.

Portable access to wireless LAN. The increasing mobile users become WLAN
candidates. Laptop and wireless NIC enable user to travel to various locations while
remaining their access to networked data.

Multimedia over wireless networks. Wireless packet-switched LAN deal with realtime services like voice and video.

Wireless remote data access. People can access data or files stored on servers at home
of office wherever he is physically be. The servers function as Internet data/file
station.

Data Backup. Mission-critical applications can be implemented with a wireless
backup in the case of malfunctions in the wired infrastructure.
3.8.
Network Design Plan Analysis
There exist different alternatives for Wireless LAN setup. This can be simple or complex
depending on the number of expected users, area of coverage, quality of service, service
types. The network topology for WLAN can broadly be classified into the following two
types [71]:
77

Ad-Hoc WLAN. This topology is very simple. It consists of few devices (desktops,
laptops etc) each equipped with wireless adapter cards (a NIC card such as an ISA or
PCMCIA card installed through a PC card slot). This does not require a central server
(or administrator) or preconfiguration, so long as all the devices in the network are
within each other's range. This is not connected to the outside world, just that these
devices in the network are connected to each other, as shown in Figure 24. Hence this
has limited access and use. This type of network is also called wireless peer-to-peer
network. This is very suitable for group meeting, conference etc. The range of this
network depends on the products used, and data rate asked for. Table XIII shows
possible ranges for different data rates for 802.11b products.
Figure 24. Ad-hoc WLAN
Table XIII. Ranges possible for different data rates

RANGE
DATA RATE
100FT
11MBPS
150FT
5.5MBPS
300FT
2MBPS
Client-Server based WLAN. As already discussed ad-hoc WLAN has limited use and
is confined to a small region. But most of the time a WLAN is implemented as a
complementary extension to existing wired client server network. In such scenarios
the devices in the WLAN are capable of getting connected to the outside network
through wired backbone networks using Access Points (APs) along with a seamless
78
connection among themselves (either a direct wireless connection or through one or
more APs or Extension Points (EPs), as shown in Figure 25). AP acts as a connection
point between WLAN and existing wired network (which is high speed Ethernet in
most cases). Each AP effectively doubles the network range (compared to peer-topeer network) at which devices can communicate. Each AP can accommodate a
specific number of clients depending on nature of transmission involved, required
QOS etc. At present, many real-world applications exist, where a single AP serves
from 15-50 client devices [71]. These APs have finite range (in the order of 500 feet
in indoor environments and 1000 feet outdoor environments, which put a limit on the
coverage of network using one AP. To extend the area of coverage, multiple APs are
used and to ensure seamless roaming the coverage areas of different APs are made to
overlap. This type of network configuration is used in offices, educational institutes,
warehouses, etc, where the coverage area is large. Up till now, we are considering
that each AP is connected to the wired network, which is not a good and practical
option always, especially in cases where the area to be covered by such a network is
far from the wired network. To take care of such cases, Extension Points are used, as
shown in Figure 25. EPs look and function like APs, but the difference is that they
connect to APs not to the wired network. They extend the network by relaying the
signal from a client to an AP or another EP.
Figure 25. Client-server based WLAN
Although network design requirements, building environments, building materials
vary much, and different equipment vendors’ products have different parameters, there
exist some common principles in WLAN design, for both IEEE802.11 and HiperLAN.
The overall coverage area and the throughput of the WLAN system are the two
basic categories of performance metrics should been studied very carefully.
The overall coverage area is the region in which mobile users can receive signals
from access points in the WLAN system. It can be evaluated in terms of received signal
79
strength intensity (RSSI). Measuring RSSI could be performed by system monitoring
software coming from equipment vendors. There also exist some simulation software to
simulate and predicate the expected coverage area. After comparing the measured data
and predicated data, WLAN architects may need to re-locate some access points to fulfill
the design requirement and reduce signal leakage from the defined coverage area.
Throughput defines how quickly the mobile users can send and receive
information over the WLAN. Measurements data should be collected from different
locations of the coverage area. In most case, WLAN architects may establish a clientserver communication link via TCP connection, to identify throughput at any location.
Although there are some impacts (such as overhead of protocol, other traffic on the
network), such data could tell what a user may experience in the actual network. The
measure should be taken at any region during various periods, such as normal network
traffic, a much less one and a much exceeding one. And then make an average
throughput. The impact of loading on the access points needs to be performed too.
Implementations of handoff and dropping are the responsibility of manufacturers,
since they vary according to different equipments.
A certain level of received signal strength must be present to enable a
communication between mobile users and access points. In practice, this level may be –
90dBm, and may vary among different manufacturers. Considering the impact of
loading, increased traffic will shrink the service area, so this value may be changed to a
increase signal strength of –75dBm.
Security issues need be considered carefully. Signal leakage is a major concern,
and present a potential security threat. Signals transmitted in a WLAN can penetrate
through building walls and floors. WLAN architects should keep the access points away
from windows, thin outside walls and other building materials, which could be penetrated
by signals easily and thus result in risk of security.
Currently, the traffic engineering issues are under research. Some projects plan to
exploit the potential of IP-based wireless mobile multimedia networking for WLAN. One
major purpose is to develop a set of enhanced/new IP-based techniques to support
mobility and soft-guaranteed QoS for WLAN. They should also develop location-aware
and QoS-aware application services for mobile users. UMTS Release 5 will add
additional rationale for unique addressing and predictable performance delivery of realize
wireless multimedia contents for WLAN.
Wireless operators should provide transactional and multimedia environments for
their customers with performance guarantees, especially for those time-critical and realtime applications. IPv6 has mobile IP concept. The IPv6 standard also use the Flow Label
in header to enable QoS, and supports traffic engineering of flow in a MPLS (Multi
Protocol Label Switching) fashion. So, both IPv6 and MPLS techniques should be
utilized in the traffic engineering of WLAN. The combination of Differential Services
(DiffServ), MPLS and proper network traffic engineering could provide application
specific QoS.
80
In order to offer dual IPv4 and IPv6 solutions, NAT-PT (Network Address
Translation-Protocol Translation, RFC 2766) will be used to connect IPv6 mobile
terminals and IPv4 ones during early deployment phase.
3.8.1.
Description of Possible In-Building Network Design
Alternatives using the WLAN Technology and possible
external interference/interoperability
WLAN can be deployed inside of a building using the Client-Server based WLAN
Configuration. In most cases one or two APs will be sufficient to cover each floor and
then different floors can be connected through EPs. These APs can be connected to the
existing wired infrastructure of the building, which is high speed Ethernet in most cases.
There exist many sources of potential interference, to in-building WLAN, because
there are many more devices which also operate in the same ISM band used by the
WLAN Technology. Microwave oven, which operates at 2.4GHz, is potential source of
interference for WLAN devices, operating around same frequency. Also some cordless
phone work at 5GHz, which are sources of interference to the WLAN devices designed to
operate around 5GHz U-NII (Unlicensed National Information Infrastructure) band.
The interoperability issue can be looked upon from two angles: first is
interoperability between WLAN devices from different vendors and then interoperability
between different technologies (which exist or going to come in near future). The first
issue is being taken care, by standard bodies and manufactures, making sure that products
from different vendors can work with harmony. The second issue is still under research,
with few existing solutions, as discussed in Section 3.6.
3.8.2.
Coverage and Capacity Analysis as a part of Network
Design Process
If the coverage area is small (less than 500ft in radius) and also only communication
between the devices in the network is needed, ad-hoc WLAN can be used. Here the
number of users will be limited by factors like required QOS, service types, and so on.
But in most cases the Client-Server based WLAN is preferred. This can give coverage to
a much bigger area, using appropriate number of APs and EPs. Typically one access
point gives coverage of around 100m in 802.11b standard and can handle around 15-50
users [71].
3.9.
Network Deployment Technology and Premise Network
Security Plan
Compared to wired system, signal communication security over WLAN is an obvious
challenge, since unauthorized eavesdroppers and hackers can access the data
communicated over WLAN even they are not in the physical proximity. There are a set of
secure WLAN solutions available for different customers to choose according to their
own network.
81
802.11 APs can be cond with a service set identifier (SSID), but it is not enough
for security (???). For most enterprises, they can use VPN technologies built into or on
top of WLAN products.
The wired equivalent privacy (WEP) option of 802.11 standards or the common
128-bit extension of WEP is useful for many WLAN implementations. WEP technique
uses shared keys and a pseudo random number (PRN) as an initial vector (IV) to encrypt
the data portion of network packets, but does not encrypt 802.11b WLAN network
headers. Each station (clients and APs) has a number of keys to encrypt the data before it
is transmitted through the airwaves. Each station can only receive a packet being
encrypted with its appropriate key. Without proper key, the packet will be discarded by
the station and never delivered to the host. Some vendors also provide key servers to
implement centralized key management, such as Cisco.
The Internet Protocol Security (IPSec) specification defined by the IEEE is the
most widely used mechanism or securing VPN traffic. IPSec can use DES, 3DES and
other bulk algorithms for encrypting data, keyed hash algorithms (HMAC, MD5, SHA)
for authenticating packets, and digital certificates for validating public keys. IPSec
includes 3 main elements: Authentication Header (AH) Encapsulation Security Payload
(ESP) Internet Key Exchange (IKE).
For business networks, a VPN solution for wireless access is the best security
measure for WLAN. A VPN is a private network that creates a secure tunnel in which
data can flow. Already widely used for remote access, VPNs employ various security
mechanisms to ensure that only authorized users can access the network and that the data
cannot be intercepted.
The combination of VPN and, IPSec is an ideal solution for today’s wireless
networking security needs [90]. With this solution, wireless APs are simply configured
for open access with no WEP encryption, because the VPN channel handles security.
VPN servers provide authentication and full encryption over the WLAN. The use of
digital certificates offers strong authentication, and even in the event of unauthorized
access, the WLAN communications cannot be read or used.
Bluetooth also uses keys to encrypt data. There are several kinds of keys in the
Bluetooth system to ensure secure transmission [72]. The most important one is the link
key, which is used between two BT devices for authentication purposes. There are four
types of link keys: unit key, combination key, master key and initialization key. All of
them are 128-bit random numbers and are either temporary or semi-permanent.
Encryption key can be derived by using link key. This secures the data of the packet and
is regenerated for all new transmissions. Each time encryption is needed, the encryption
key will be automatically changed.
Even if there is not a key, there is the PIN code, which can be used to help
identify devices to each other. It is a user-selected or fixed number, normally 4 digits in
length, but it can be anything between 1 to 16 octets. The user can change it to add
security to the system.
Many vendors have their own optional security systems. For example, Ericsson
provides a firewall unit attached to each radio access point to forces every wireless user
82
to authenticate his or her identity, besides encrypting any data exchanged over the air by
means of IP-layer encryption. The firewall unit prevents unauthorized users from
accessing the LAN or from eavesdropping traffic that is broadcast in the corporate
environment. To achieve this, the firewall unit uses a powerful encryption scheme that
complies with the IPSec standard—set by the Internet Engineering Task Force (IETF)—
which is designed to provide a security level sufficient even for companies with very high
security standards.
Some operating systems have upgraded to simplify to address security for the
WLAN. For example, Microsoft Windows XP operating system incorporates the new
802.1x-standard VPN security technology for authentication and encryption key
exchange, so it may simplify the security decision-making [73].
3.10.
Network Deployment Scenarios
WLAN deployment is easy compared to other types of networks. There are different
types of topologies which are suitable for different applications. Out of all these, the
following two configurations are most widely used.

Peer-To-Peer WLAN. This is the most basic form. It is also termed as an ad-hoc
topology in which a LAN is created solely by the wireless devices themselves, with
no central controller or access point. Each device communicates directly with other
devices in the network rather than through a central controller. So such network just
requires PCs equipped with wireless adapter, enabling the PCs to share resources with
one another, as shown in Figure 24.

Client-Server based WLAN. In a Client-Server based WLAN, users are benefited
from extended range. They also get connected to the outside networks through Access
Points. The APs are connected to the wired backbone as a server to provide resources
for users (as shown in Figure 25). The number of users supported varies according to
different technologies and different kinds of transmissions. The typical number
ranges from 15 to 50. In this configuration EPs are used to extend the network
coverage to locations which are far away from the wired backbone network.
In-Building WLAN can be arranged in a peer-to-peer (ad hoc) topology using
only client adapters. A wireless LAN transceiver acts as a hub to bridge between wireless
and wired networks. When the range is enlarged, access points can be incorporated to act
as the center of a star topology and function as a bridge to an Ethernet network. Within a
building, WLAN support both mobile and connected computer. Users can move freely
within a facility while maintaining access to the network.
Networks located in buildings with miles from each other can be integrated into a
single local-area network with a wireless bridge, thus from a building-to-building
WLAN. This is much more convenient than bridging between buildings in wired way in
case of obstacles such as freeways, lakes, regulations of local governments. It is also
economic to eliminate the fees of leased line. Immediate and easy installation is another
benefit.
83
For HIPERLAN/2, it relies on cellular networking topology combined with an adhoc networking capability. It supports two basic modes of operation:

Centralized mode. This mode is used in the cellular networking topology where each
radio cell is controlled by an access point covering a certain geographical area. A
mobile terminal communicates with other mobile terminals or with the core network
via an access point. This mode of operation is mainly used in business applications,
both indoors and outdoors, where an area much larger than a radio cell has to be
covered.

Direct mode. This mode is used in the ad-hoc networking topology, mainly in typical
private home environments, where a radio cell covers the whole serving area. In this
mode, mobile terminals in a single-cell home "network" can directly exchange data.
3.11.
Network Cost Analysis
It is very important to know the cost equations of a particular network type before going
for its deployment. In fact, in the present scenario this has more practical meaning as
there exist multiple options to satisfy one particular type of network needs. For example,
to set up a small range we can either go for WLAN or Bluetooth or can decide to add our
area to the larger cellular network using repeaters etc. WLAN is proved to be cost
effective compared to its wired counter-part. Even though the initial cost of WLAN is
more compared to the wired one, once installed it has little management, expansion,
trouble-shooting and relocation expenses. Hence, comparing the overall cost involved
WLAN has been proven to be cheaper compared to the wired alternative.
3.11.1.
Identification of the cost of various components involved in
Wireless LAN setup
Different components of WLAN are Access Points, PC card, PCI Adapter, Wireless
Bridge. These components are manufactured by different vendors, e.g., 3Com, Apple,
Avaya, Cisco, IBM, Nortel, Nokia, Symbol, Zoom, and many more.
The following table gives a brief price comparison of there various components
[74].
84
Table XIV. Price comparison of different components of WLAN provided by major
suppliers
Vendor Name
3Com
Apple
Avaya
Cisco
Compaq
Ericsson
IBM
Nokia
Nortel
Symbol
Zoom
3.11.2.
Access Points
$545.00
$301.00
$685.00
$717.00
$729.00
$929.00
$1015.00
$751.00
$1065.00
$1025.00
$410.00
PC card
$169.00
$99.00
$144.00
$193.00
$166.00
$186.00
$182.00
$212.00
$289.00
$181.00
$136.00
PCI Adapter
$199.00
-$59.00
$269.00
$208.00
--$199.00
-$271.00
$136.00
Wireless Bridge
$1095.00
--$458.00
----$638.00
$655.00
$1888.00
Analysis of the total Economics Involved in Deploying and
Running such WLANs
In most cases the initial installation cost for the WLAN is more compared to an alternate
wired network, but the running cost for the WLAN is much less. Because of this, the
payback period of this is much less compared to wired one. Survey across industries
using WLAN has shown that the typical payback period in case of WLAN is around one
year [75]. This survey has also shown that on average the cost per user for WLANs is
around $4,550.00. Market analysis has shown that WLANs are extremely cost-effective
for organizations using this technology for large scale network deployment. For example
organizations that implemented WLAN for around 300 users has been benefited from
annual savings of up to $4.9 million which corresponds to per user saving of $15,989.00.
In some cases even the initial installation cost of WLAN has been found to be less
than the wired alternative. University of Akron, covered their four-story library with
WLAN with a total cost of $80,000, using Cisco Airnet 350 series and the estimated cost
for wired network for that was $800,000 [76].
All these shows that along with other advantages WLAN alternative is also costeffective. With the technology developing and more competition in market, WLAN
products are becoming cheaper, which will make their deployment even cheaper.
3.12.
Conclusions
In this report, the technologies of WLANs were comprehensively investigated. The issues
such as interference and environmental problems were also analyzed. The network
deployment scenarios and design plans were briefly discussed. Moreover, the market
size, market penetration, and costs of WLANs were addressed. Because of its advantages,
WLANs will be an important part of next generation wireless networks.
85
4.
Wireless PBX
4.1.
Overview
A Private Automatic Branch eXchange (PABX or PBX) is a private telephone system
within an enterprise that switches calls between the enterprise users on local lines
automatically [84]. It allows all users to share a certain number of external phone lines.
The PBX is owned and operated by the enterprise rather than the telephone company.
Most mid-sized and large organizations use a PBX because it is much cheaper than
connecting an external telephone line to each telephone in the organization. A wireless
PBX (WPBX) does not function as a stand-alone PBX. Instead, a WPBX works together
with a conventional wire-line PBX. It provides call forwarding to extensions, accessing
voice mail, intelligent switching and end-to-end transmission. WPBXs enable users to
carry their telephone handsets inside the building and be accessible wherever they are
[85]. A WPBX system can be integrated with a wireline PBX to provide mobility
capability to a conventional wire-line telephone system. When integrated into an
organization's PBX, wireless service allows the user to use a portable handset as a
wireless extension to his desktop telephone. This allows users to keep the same extension
number, and features of their desktop handsets with the freedom, and convenience of a
mobile phone.
A WPBX system typically involves three components: control unit, base station
and wireless handset. The control unit functions as a gateway between the wireless
system and the wireline PBX systems. The base stations of the WPBX are located within
the building to relay wireless signals through antennas to wireless handsets. The wireless
handset is a small digital telephone emulating the feature functionality of the PBX's
traditional desktop phones. Wireless PBX systems provide seamless communications
throughout the building, even in places like elevators, tunnels, or parking lots where the
signal reception is poor. Wireless PBX users benefit from the same digital voice quality
as conventional PBX users.
In this chapter, the technology, the characteristics, and the network deployment
strategies of WPBX systems will be presented.
4.2.
Technology Analysis
Wireless PBX systems provide users with a high degree of mobility. The wireless
handsets can be used anywhere within the coverage of the system's base stations, and
provide the voice quality of the wireline telephone network. The major components of
wireless PBX systems such as base stations and antennas must be strategically placed
within the coverage area to ensure seamless coverage and high-quality service.
4.2.1.
Current Technology of WPBX
A WPBX system consists of the following three components:

Control unit: The control unit routes all incoming and outgoing calls between the
wired telephone switch, and the base stations. The control unit can be co-located with
86
the telephone switch or connected to the switch with a twisted-pair wiring or optical
fiber from several thousand feet away. Optional battery backup is usually available,
permitting uninterrupted operation in case of a power failure. System control,
management, and administration functions are provided by an attached terminal that
is password protected to guard against unauthorized access. Since the control unit
becomes an integrated part of the company's existing telephone system, users have
access to most of its features through their portable phones. Users can even set up
conference calls, forward calls, and transfer calls. Depending on the wireless system
installed, up to several hundred handsets can be supported by a single WPBX.
Additional control units can be added as necessary to support future growth.

Base station: The base stations are placed strategically within an enterprise to relay
wireless signals via antennas to the wireless handsets in the coverage area. They are
typically mounted on the ceiling or walls, and are connected by twisted-pair cables to
the wireless controller. They send and receive calls between the wireless handsets and
the control unit. As the user moves from one cell to another, the base station hands off
the call to the base station into which the user moved. When the new base station is
able to receive the signals from the user's handset, the channel of the previous base
station becomes idle, and it can be used to handle another call. To facilitate the
handoff process, each base station may be equipped with dual antennas to provide
antenna diversity. Antenna diversity is used in narrow-band systems to deal with
multi-path fading. Multi-path fading is a serious problem also for the in-building
wireless systems because of the reflections from walls, furniture, etc. Antenna
diversity improves signal detection, enabling the handoff to occur in a timely manner.
The base station accomplishes this by sampling the reception on each of its antennas,
and switching to the one that offers the best reception. This process is continuous,
ensuring the best voice quality throughout the duration of the call. Some vendors
offer optional external antennas for outdoor coverage or directional indoor coverage.
Also, the use of spread spectrum technology by some vendors virtually eliminates the
multi-path problem. In densely populated areas, the number of base stations can be
increased to handle a greater number of calls.

Wireless handset: The wireless handset is a pocket-sized digital telephone that
emulates the feature functionality of the PBX's traditional desktop phones. They can
also be used independently by assigning telephone numbers of their own. Typically,
each wireless handset has a unique identification number that must be registered with
the control unit. This allows only authorized users to access the in-building wireless
communication system. If the handset is assigned the same number as the user's
desktop phone, both phones ring for an incoming call. The user can even start a
conversation on one phone and switch to the other. If the wireless handsets and the
desktop phones have different numbers, each can be programmed by the user to
forward incoming calls to the other. In either case, the wireless handsets must be
registered with the control unit. If the handset is equipped with a liquid crystal display
(LCD), the unit can also be used to retrieve e-mail messages, faxes, etc. However,
this requires a separate messaging interface or access to the PBX's integrated
messaging capability through a digital station interface.
87
4.2.2.
The Frequency Bands
In-building wireless communications systems currently operate in several frequency
bands. These include the 800MHz band used for narrow-band cellular service, the
900MHz band currently used for in-building systems, the 1920MHz-1930MHz band used
for unlicensed Personal Communications Services (U-PCS), and the 2.4GHz band
utilized by some vendors to integrate LAN and the wireless voice communication
systems.
Systems operating in the 800MHz, the 1900MHz, and the licensed PCS bands can
be frequency-coordinated with a cellular carrier to offer the advantage of roaming
between the corporate network and the public cellular network. Thus, the same mobile
handset can be used at work, on the road, and at home. However, this advantage is not
available to U-PCS wireless solutions, because U-PCS systems operate with a completely
different technology that is incompatible with any licensed service. Other wireless
systems use the 902MHz-928MHz frequency band that is intended for wireless
communication within very narrow geographical areas. Even if wireless systems use the
same frequency band, they may not be interoperable because of different underlying
transmission technologies like CDMA or TDMA. In fact, most in-building WPBX
systems are incompatible.
4.2.3.
4.2.3.1.
Products by Leading Vendors
Link WTS by SpectraLink
The Link WTS (Wireless Telephone System) [86] connects to a facility's existing
telephone system. A network of base stations is installed throughout the facility. The call
center mobility is supported via SpectraLink's ccLink WTS. The technical specifications
of this product are as follows:

Frequency band: 902MHz - 928MHz

Access technology: TDMA / Frequency-Hopping Spread Spectrum
4.2.3.2.
Companion by Nortel
The Companion [87] portfolio of in-building wireless communications solutions provides
cost-effective, mobile communications at work. It enables users to be anywhere within
their workplace for both voice and WCTI data communications. The technical
specifications of this product are as follows:

Frequency band: 1920MHz - 1930MHz

Access technology: FDMA / Time Division Duplex (TDD)
88
4.2.3.3.
MD110 by Ericsson
The MD110 [87] is a full-scale cordless PBX, supporting both physical and functional
integration of DECT (Digital Enhanced Cordless Telecommunications) in a fully modular
and distributed business communications system. The technical specifications of this
product are as follows:

Frequency band: 1900MHz

Access technology: TDMA / TDD
4.2.3.4.
NEAX WCS by NEC
NEAX WCS (Wireless Communication System) [89] provides the employees of an
organization with a full-featured wireless extension to their desktop telephones. Access to
advanced telephony features such as voice mail, call forwarding, and conferencing can
also be provided. The technical specifications of this product are as follows:

Frequency band: 1920MHz - 1930MHz

Access technology: TDMA
4.3.
Characteristic Analysis
There are various types of WPBX systems available in today's market. However, WPBX
systems can be mainly classified according to two criteria: operating frequency and
access technology.
WPBX systems are based on the following access technologies:

CDMA: CDMA is a spread spectrum technology that assigns a different code to each
wireless phone call. The CDMA-based systems recognize each call by its code and
process the call. The same frequency band is shared between all users simultaneously.

FDMA: FDMA works by allocating a separate frequency band to each user to support
multiple, simultaneous wireless access. Several WPBX products, like Companion by
Nortel, are based on this access technology.

TDMA: TDMA works by splitting each frequency band in the time domain into
multiple time slots. This access technology is adopted by many vendors such as
Ericsson, NEC, SpectraLink, Avaya, etc.
The WPBX systems operate in the 800MHz band, the 900MHz band, the
1920MHz-1930MHz band (U-PCS), and the 2.4GHz band. The following are the
characteristics according to the frequency band used:

800MHz and 1900MHz: Systems operating in these bands can be coordinated with a
cellular carrier to offer roaming between the corporate network and the public cellular
network. This enables the same wireless handset to be used everywhere.

900MHz and 2.4GHz: Systems operating in these frequency bands may cause
interference problems with other equipment operating in the same frequency bands.
89

1920MHz-1930MHz: The U-PCS frequency band is allocated by the FCC. Systems
operating in this frequency band cannot support roaming between the corporate
network and the public cellular network. U-PCS systems do not encounter
interference problems because this frequency band is allocated specifically for inbuilding wireless use.
4.4.
4.4.1.
Main Target Market Deduction
Current Wireless PBX Market Segments
Wireless PBXs have been on the scene for almost ten years. They are available from a
wide range of suppliers such as Ericsson, Lucent, NEC, Nortel, Siemens, and Spectralink.
In the year 2000, combined sales of WPBXs and wireless key systems reached $275
million. In some European markets, for example, in France and Italy, more than 10% of
the new PBX stations are wireless; in Finland, Sweden and Denmark, WPBX stations
account for more than 25% of the new station shipments [77]. However, in United States,
wireless communications within the office, in particular wireless options for the PBX,
have not taken off. Less than 5% of the new PBX station shipments are wireless.
There are several reasons for the relatively low shipment in the U.S. like pricing,
technology, customer awareness and education. Among these, pricing is the main reason.
The cost per user for a WPBX system is sometimes three times of a conventional wired
desktop phone. However, since in-building wireless communications is growing rapidly,
ample opportunity exists for manufacturers with innovative products and applications.
Customers want cordless telephones, full roaming, and seamless handoff during calls.
Multiple product lines, broader distribution channels, and increased roaming capability
are the highlights of wireless vendors' current market strategies [80].
4.4.2.
Market Forecast
Currently, the growing market trends are:

Wireless communications expansion outside the building.

Cellular communications expansion inside the building.

Wireless IP-based systems running over enterprise LANs for adding wireless
communications to existing data network infrastructure.

Mobile data and voice communications from handheld devices such as pagers and
personal digital assistants using WAP (Wireless Access Protocol) technology.
The market for WPBXs is changing rapidly. It is forecasted that by 2005, the
market will have exploded to almost $840 million, over a factor of three to one from the
base year of 2000 [78].
90
4.5.
Technology Development Prospect Analysis
As the wireless in-building communication becomes more common, it is expected that
the WPBX technology will have the following advancements in the future:

Convergence of telephony with IP
There is an increased demand from employees who are mobile and require both
wireless voice and data communications to perform their jobs effectively and
productively. Wireless IP-based systems running over enterprise LANs for integrating
wireless telephony with the existing data network is the trend of technological
development. Enterprise networks will evolve to an IP-based architecture that can
handle voice, video, and data. Considering the investment in wireless LANs, it is
more economical for enterprises to overlay voice over the wireless LAN rather than
installing a dedicated, WPBX. Because voice and data traffics are combined on a
single network, the quality of the voice call should be maintained while data
performance is kept high.
Currently, both SpectraLink Corporation [81] and Symbol Technologies [82] have
released voice-over-WLAN products, named NetLink Wireless Telephone System
and NetVision Phone System, respectively.

Integration of Enterprise and Cellular/PCS Systems
This solution is for both on and off-premises communications. It relies on cellular
technology. The key to this solution is to program cellular service to function like a
PBX. Compared to conventional WPBXs, users can save money because they need
only one handset that can be used both inside and outside the office. In addition, users
no longer need multiple business phone numbers.
Ericsson and AT&T are working to achieve this goal. We will discuss the services
provided by this solution in detail in the next section.

Compatibility
Currently, WPBX portable telephones are specific to each system. Although different
systems may operate in the same frequency range, each one conforms to different
wireless transmission standards. Even systems from the same vendor may not be
compatible. For example, Lucent's Definity Wireless System can not interoperate
with its TransTalk Wireless System. The former operates in 1910-1930MHz
frequency range, while the latter operates in the 900MHz range. Interoperability
among in-building WPBX systems is one of the future research topics.
Telecommunications Industry Association (TIA) has a standard for IP telephones
[79]. It specifies requirements for the interoperability, acoustic performance,
supplementary services support. It also provides specifications for safety,
electromagnetic compatibility, and environmental performance of Voice-over-IP
Feature Telephones.
91
4.6.
Interworking / Integration Technology Analysis with IMT2000
The International Telecommunications Union (ITU) defined the world standard IMT2000 (International Mobile Telecommunications). IMT-2000 now consists of five
standard committees:

IMT DS, widely known as UTRA (UMTS terrestrial radio access) based on W-CDMA

IMT MC, widely known as cdma2000

IMT TC, also called TD-SCDMA

IMT SC, also called UWC-136 (EDGE)

IMT FT (DECT)
The DECT (Digital Enhanced Cordless Telecommunications) standard is one of
the core building blocks for 3G communications. It will play a central role in the
convergence of fixed and mobile communication services. DECT is designed for shortrange use as an access mechanism to the main networks. It offers cordless voice, fax,
data, and multimedia communications, wireless local area networks, and WPBX. It
supports applications like single-cell domestic cordless phones, multi-cell WPBX
systems, and wireless local loop systems for fixed users.
Wireless PBX technology works efficiently with the DECT technology to cover
large business complexes with a cellular structure using small cells. A multi-cell DECT
WPBX system can form a seamless mobile communications environment. The DECT
digital radio technology, designed for indoor coverage, can handle a large number of
users getting both voice and high-speed data services with a single infrastructure.
Wireless PBX systems will continue to inter-work with the DECT technology to follow
the evolution of 3G wireless networks.
92
BTS
PBX
In-building WPABX
system
IP Core Network
BTS
BTS
BTS
3G network
Figure 26. WPBX inter-operation with 3G systems
Figure 26 shows how the in-building wireless PABX system can be inter-operated
with 3G network system. The in-building WPABX system is connected through PBX to
the IP core network. 3G network is also connected to the IP core network. When a user
moves from 3G network to a building equipped with WPABX system, a smooth roaming
can be provided via the BTSs in the building WPABX system which is connected
through PBX to the IP core network. Thus, the users getting various services in 3G
networks will be able to get the same services within the buildings equipped with
WPABX system which has inter-operability with 3G systems.
4.7.
Service Analysis
A WPBX adds the mobile capability to a conventional wireline telephone system. When
integrated into an organization's telephone system, the WPBX enables users to use a
portable telephone as a wireless extension to their desktop telephone. This allows users to
keep the same extension number and features of their desktop handsets with the freedom
and convenience of a mobile phone. This is called "on-site mobility". There can also be
significant savings in wiring in areas that are difficult or expensive to wire, like elevator
and parking lots.
Wireless PBX systems also allow the integration of mobile cellular services and
local cordless PBX services. When the users are in their offices, their mobile phones
93
serve as personal extensions to the company's PBX. Incoming calls to users are handled
by the company's PBX system. When the users leave their offices, the phones function as
ordinary mobile phones. Any incoming calls to users are routed to the mobile phones via
public wireless network. This service allows users to carry just one handset with one
number no matter where they are. It allows immediate and direct communication. This is
called "off-site mobility". Off-site mobility eliminates delays and allows users to work
away from their desks without fear of missing critical calls. It gives users great mobility
and versatility. This service can increase the productivity in a company, reduce phone tag
and paging load.
The integrated system also has the capability to map the four-digit PBX extension
to users' cellular phones. It gives the users ability to call or be called by others in the
office using just assigned extension numbers, regardless of their location. For example, if
a user at home wants to get in touch with a colleague, he just needs to dial his colleague's
four-digit company PBX extension number. If his colleague is out of the office, the call
will be automatically relayed to the other party's wireless phone via the public network.
The improved intelligent billing service is another advantage of the WPBX
system in addition to the flexible mobility capability. Calls within the company and calls
using the PBX extension numbers are billed at a lower cellular rate for on-site services.
For example, AT&T offers the Enhanced Personal Base Station (EPBS) option for its
cellular network that provides personal base stations for the home. The base station
consists of a small transceiver mounted on the exterior wall of the customer's premise. It
communicates via the digital PCS cell sites to AT&T central offices. Users pay a flat
monthly fee for the privilege of using their cellular phones at home, on the road, and at
the office. When the user is on the road, calls are billed at regular cellular rates. When he
arrives at work, the network automatically launches a cellular connection to the
company's PBX. Calls are then billed at the company's on-site telephone rate.
4.8.
Network Design Plan Analysis

Currently, there are three technology options for wireless telephone solutions
depending on the services described in the previous section [80]:

Fully integrated in-building wireless voice systems from traditional PBX vendors, like
Ascom, Avaya, Ericsson, Nortel Networks, NEC, and Toshiba, and adjunct systems
from vendors like SpectraLink.

Cellular/PCS-based systems, like Ericsson Mobile Advantage and AGCS ROAMEO,
which support both public cellular and in-building wireless calls from the same
handset.

The 802.11-based networks, which integrate wireless voice communications with
LAN infrastructures to support both voice and data communications over a single
backbone. Examples are NetLink WTS from SpectraLink and NetVision Phone System
from Symbol Technologies.
94
There is no interoperability among in-building wireless voice systems from
different vendors, except those systems that support the 802.11 standard for wireless
voice communications.
Integrated wireless solutions have the wireless radio controller installed in the
same cabinet with the telephone switch. Usually, the integrated wireless telephone
solution is manufactured by the vendor of the switch. Wireless adjunct systems from
third-party vendors, such as SpectraLink Corporation and Symbol Technologies,
typically locate the radio controller near the telephone switch, where it is directly
connected to the base stations.
In this section, we focus on the first and third network design options, i.e.,
integrated in-building wireless telephone system and 802.11-based voice/data
communications. From the end user's perspective, these two options provide the same
functionality and quality. The choice is based on the customer's infrastructure and
management preferences. The first option is an economical choice for customers who
need to implement a wireless voice-only solution. Because 802.11 is an international
standard for WLANs, the third option is good for wireless telephony throughout the
global enterprise. We choose the products from SpectraLink as examples to explain the
network design alternatives. Network design plans from other companies are similar.
4.8.1.
4.8.1.1.
Wireless Telephone Solution for Mobile Communication in
the Workplace
System Overview
The Link Wireless Telephone System (Link WTS) architecture developed by SpectraLink
Corporation [81] is shown in Figure 27. By placing small digital radio transceiver
systems called base stations throughout a building or campus, users can initiate and
receive calls anywhere in the facility using portable wireless telephones. The wireless
telephone system attaches to a local PBX, key system or Centrex service. Since all calls
are routed through the local phone system, there are no air-time charges or monthly usage
fee.
95
Figure 27. Link wireless telephone system architecture
The Link Wireless Telephone System includes:

Master Control Unit
The Master Control Unit (MCU) is a compact and modular unit that connects the
telephone switch to the wireless telephone system using digital and/or analog line
interfaces. The digital interface technology makes advanced switch features available
to wireless telephone users, such as multiple line appearances, and display features.

Base Stations
The base stations are fixed transceivers that provide radio coverage throughout the
workplace. They are small and lightweight, and can be installed in a variety of
locations. The base stations are placed to provide adequate overlap and coverage.

Wireless Telephones
The Wireless Telephone is specifically designed to meet the requirements of inbuilding mobile communications.
4.8.1.2.
Capacity and Coverage
SpectraLink offers Link 150 MCU and Link 3000 MCU. The system capacity and area
coverage of these two systems are listed in Table XV.
Table XV. System capacity and area coverage
MCU
Link 150
Link 3000
Wireless
Telephone
64
3,200
System Capacity
Base Stations
Simultaneous
Calls
16
32
1,000
1,600
96
Area Coverage
Max. Coverage
1,500,000 sq. ft.
100 million sq. ft.
4.8.1.3.

Interfaces
Open Application Interface
SpectraLink's Open Application Interface (OAI) is an integrated applications
programming interface for computer telephony integration. It enables third-party
computer applications to communicate with the Link WTS. It is the information
access for the WPBX system. This feature allows users to view and respond to
alphanumeric messages that are displayed on the wireless telephone. Message
exchange occurs in real-time. The benefit of the OAI is its ability to quickly respond
to non-voice messages, enabling fast decision-making and increased productivity for
wireless telephone users.
The OAI allows the application program to access the status and control features for
the display, keypad, icons, and ringer of the wireless telephone. Using the OAI, the
wireless telephone allows the user to receive and retrieve important information from
external systems.

Digital Switch Integration
SpectraLink offers digital interfaces to a wide variety of PBXs and key telephone
systems. The LinkPlus technology implements digital interfaces by emulating
proprietary digital telephone sets. It makes switch features available to wireless
telephone users without requiring any switch upgrades or enhancements. Mobile
users have the ability to screen calls, access multiple lines, and use switch features.
LinkPlus allows the WTS to connect to the host PBX or key system using the same
digital station ports that are used for digital wired telephone sets. For each type of
PBX or key system, the WTS emulates all the codec, display, control, and signaling
functions of a specific proprietary digital telephone set.
4.8.2.
4.8.2.1.
Wireless Voice and Data Solutions Over Local Area
Networks
System Overview
The NetLink Wireless Telephone System (NetLink WTS) by SpectraLink operates over
IEEE 802.11-compliant WLANs, providing both voice and data communications over a
single integrated network. The system architecture is shown in Figure 28. The NetLink
WTS uses Voice-over-IP (VoIP). To ensure excellent voice quality, SpectraLink
developed a voice prioritization mechanism for 802.11 access points and Wireless
Telephones. Based on the IEEE 802.11 standard for wireless LANs, the NetLink WTS
provides a single solution for wireless telephony throughout the global enterprise.
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Figure 28. NetLink wireless telephone system architecture
The NetLink Wireless Telephone System includes:

NetLink Telephony Gateway
The NetLink Telephony Gateway provides an interface between the Ethernet LAN
and the host telephone switch using digital and/or analog line interfaces. It manages
all wireless telephones on the network and converts from voice packets on the LAN
to voice circuits on the PBX. The NetLink telephony gateway also supports H.323compliant clients, allowing third-party wireless devices to initiate and receive calls
through the host telephone switch.

NetLink Wireless Telephones
The NetLink Wireless Telephone is specifically designed to meet the requirements of
mobile workplace communications. It is available in both frequency hopping and
direct sequence spread spectrum 802.11 versions.

Wireless LAN Infrastructure
Wireless LAN access points receive IP voice packets from wireless telephones and
forward them to the telephony gateway over the wired LAN.
4.8.2.2.
Capacity and Coverage
Each NetLink 150 telephony gateway supports 16 users and 8 simultaneous calls. Up to 4
gateways can be used on a network, maximizing the system at 64 Wireless Telephones
and 32 simultaneous calls. Adding more wireless telephones to a WLAN increases the
bandwidth requirement because of the increase in traffic. Depending on the manufacturer
of Access Point (AP), 3 to 7 simultaneous calls can be supported on an AP, requiring
approximately 450-1050 kbps of available bandwidth.
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The range of the radio in the wireless handset varies according to internal wall
construction, obstructions, AP output power, RF transmission type (frequency hopping or
direct sequence), and AP vendor. The typical indoor range between the wireless
telephones and AP is approximately 150 to 200 feet.
4.8.2.3.
Interfaces
NetLink wireless telephones operate as clients on the WLAN, along with other mobile
802.11 devices. APs receive IP voice packets from wireless telephones and forward them
to the NetLink telephony gateway over the Ethernet LAN. The telephony gateway
connects to the host telephone switch using digital or analog line interfaces.
Since all devices are compatible with 802.11 standards, they are able to
communicate in the same wireless network. SpectraLink developed a Quality of Service
(QoS) mechanism, SpectraLink Voice Priority (SVP). SVP gives preference to voice
packets over data packets on the wireless medium, when data and voice are competing
for bandwidth. SVP is compliant with the IEEE 802.11 standard.
4.9.
Security
The security goals of the wireless industry are to provide user authentication to deter
fraud, and to provide over-the-air privacy to deter amateur and commercial snooping.
For in-building network design employing the wireless PBX technology, many
companies add special features to their wireless PBX products to provide security
support. For example, the SpiderNET wireless PBX System from NSM Technology Ltd.
[83] employs Frequency Hopping Spread Spectrum (FHSS) Technology to support
maximum security against eavesdropping. Each portable telephone typically has a unique
identification number that must be registered with the control unit. This allows only
authorized users to access the system. In addition, when wireless voice network
integrated to IP, modifications should be made either to voice systems or data networks
in order to ensure IP network security.
4.10.
Network Deployment Scenarios
As discussed previously, there are several solutions for in-building wireless voice
communications such as cordless telephones, WPBX options, integrated wireless voice
communications with WLAN infrastructures, and cellular/PCS-based systems, etc. Main
applications for WPBX systems include:

Health care
In hospitals and nursing homes, WPBX systems provide an immediate link between
nurses and physicians. By eliminating paging delays, nurses spend more time with
patients and less time traveling back and forth to a phone. Patient care is improved
and information is shared promptly among hospital staff.

Retail
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In the retail environment, WPBX systems reduce the long hold times customers often
endure. Store managers can be reached directly to answer questions. Customers do
not have to wait long for price checks or approvals. Overhead paging is also reduced,
which creates a more pleasant shopping environment.

Manufacturing
Wireless PBX systems allow supervisors to roam the entire factory floor while
remaining in direct contact. Production downtime is reduced because maintenance
personnel are always reachable to address equipment problems, and to directly
consult outside specialists.

Corporate
Wireless PBX systems increase efficiency and productivity of the corporate. With
WPBX systems, customers can reach the right person directly rather than being
transferred into voice mail. Managers are contacted quickly when a decision must be
made. Employees have more time for their jobs, spending less time to return phone
calls.

Warehouse
Personnel in warehouses can be in touch throughout the day wherever they are on the
loading dock, conveying commodity via forklift, or pulling items from inventory.

Government
Office managers can be available at all times for decision-making issues.
4.11.
Network Cost Analysis
The main pricing elements of a WPBX system are the radio controller, base station and
portable telephones. There is no standard industry price for these elements. System
design and configuration requirements are also major factors contributing to the wide
price variation.
A base station costs $1,000 to $2,000. The cost of the wired system, which
provides the features/functions, and the cost of system switching and trunking must be
added to this price. Cost of a wired connection ranges from $200 to $1,000, depending on
the number of features (voice mail, speed dialing). A wireless connection starts at about
$600 and can rise up to $2,000. The most variable cost in any installation is the base
station, and the number required depends on traffic and cell coverage. The cost of the
portable telephone and the battery charger unit is typically priced at about $500 to $700.
The price of different system designs vary. The list price of SpectraLink WTS is
$1,000 per user. The specific price varies depending on the size of coverage area and
building construction. For the integrated system of wireless voice communications with
WLAN, the list price for a 16-port NetLink telephony gateway of NetLink WTS is
$4,000. The NetLink Wireless Telephone list price is $750. For the cellular/PCS-based
systems, i.e., programming cellular service to function like a PBX, the cost varies
according to the number of user licenses and the number of radio heads that need to be
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installed. The price of Ericsson product, digital wireless office system (DWOS), is $800$1,000 per user.
Pricing is a major issue in the in-building wireless voice system market. The longterm benefits of WPBX justify the initial cost of deployment. The increased availability,
efficiency, and productivity of properly equipped mobile workers, as well as the
enhanced customer service factor will outweigh the initial cost concerns.
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5.
Comparison of Wireless Repeater and Pico-BTS
As the demand for mobile telephony, data and Internet is increasing at more than
predicted rate, subscribers are not only expecting, but also demanding to be connected to
the mobile network all the time. The blank spots in the network are becoming intolerable
for users. Hence arise the need for total coverage by mobile network including shadowed
regions of the network i.e. tunnels, highways, in-building locations etc. Both repeater and
pico-BTS are the proposed technologies as a solution to the above issue. Even though
both of these technologies can be used as a solution for universal coverage of mobile
networks, each has certain advantages and disadvantages which makes each of those
suitable to different network deployment scenarios. This section will briefly compare
both these technologies from four major perspectives: network service, technical
characteristics, cost and market potential for network deployment.
5.1.
Comparative Service Analysis
Both the repeater and pico-BTS technologies have the advantages of providing enhanced
system capacity, reduced network cost, and easy and flexible installation. There are some
common services supported by both technologies, whereas differences are also obvious.
Both repeaters and pico-BTSs support traditional low bit-rate 2G services such as
voice transmission, medium bit-rate 2.5G data services such as those provided by GPRS,
and high bit-rate 3G multimedia services such as those provided by IMT-2000. They are
able to provide low cost, great flexibility, and high bandwidth wireless services in local
in-building environments.
However, there are great differences between these two technologies. Repeaters
are low-level network devices that simply amplify or regenerate weak signals. A repeater
just receives and retransmits signals to the destination. It does not correct corrupted data,
differentiate traffic types, or provide any other intelligent control functions. Therefore, a
repeater cannot add new control functions to the system except increasing the signal
strength. On the other hand, pico-BTSs are high-level network devices that support traffic
management, power management and mobility management. A pico-BTS has higher
layer networking protocols to provide error control, call admission control, resource
allocation, dynamic power control, and routing functions. QoS guarantees are achieved
by these protocols.
Compared with pico-BTSs, repeaters can be used in wider areas. They are not
restricted to the local or in-building areas. They are also suitable for mountains,
highways, tunnels, and large buildings where wireless coverage gaps exist due to
shadowed areas from base stations and/or the overall traffic is not very high, but
deploying additional base stations is expensive and not necessary. In contrast, since picocells usually extend to only a few hundred meters in diameter, pico-BTSs are good for
indoor mobile applications with high capacity. They are not suitable for large areas
because of their coverage limitation. However, since pico-BTSs have smaller coverage,
location-aware services can be provided and the system has better knowledge of users'
locations.
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Overall, if the system design goal is to provide indoor cellular services with high
capacity, pico-BTS is obvious the solution. If the requirement is to extend wireless
coverage to the existing system, repeaters can satisfy this requirement while reducing the
cost per coverage area.
5.2.
Technical Characteristic Comparison and Analysis
Repeaters and pico-BTSs have some similar technical features. However, they also have
some differences. We compare these two technologies in the following technical aspects:

Frequency bands
They both follow the standards which are compatible with current 2G/2.5G wireless
systems, and also follow the standards which are forward-compatible with 3G
wireless systems. Pico-BTSs are part of wireless cellular systems. They work in the
typical GSM/PCS, TDMA/IS-136, and CDMA/IS-95 frequency bands such as 900
MHz, 1800 MHz and 1900 MHz. Future 3G pico-BTSs may follow IMT2000/UMTS specifications to work in 2 GHz frequency bands. But besides wireless
cellular systems, repeaters can also be used for WLAN. The frequency bands of
repeaters working in WLAN environment are specified in different WLAN standards,
such as 2.4 GHz and 5 GHz. Typical frequencies used by repeaters from leading
wireless repeater providers are in the range of 300 MHz and 6 GHz.

Equipment structure
The structure design of pico-BTSs is more complicated than that of repeaters.
Conceptually, a repeater can be viewed as a simple amplifier. It consists of a receiver,
an amplifier, a transmitter, an isolator, and two antennas. However, a pico-BTS does
not only contain elements for physical signal transmission, but also incorporates
higher layer protocols for intelligent control, such as data link protocols, network
protocols, and transport protocols. Both repeaters and pico-BTSs can use either
directional or omni-directional antennas depending on applications and network
configurations.

Coverage
The coverage of each repeater and pico-BTS vary. A pico-BTS usually covers a picocell size, which ranges from around 50 meters to several hundred meters in diameter.
In present market, repeaters are available with ranges as small as 50 meters to that of
8,000 meters.

Interference
Both repeaters and pico-BTSs may experience interference from the equipments
working in the same frequency band. So the deployment is very important in order to
reduce interference. The surrounding areas of repeaters and pico-BTSs need to be
clear enough to avoid interferences from other electronic devices. The repeaters and
pico-BTSs should be placed with enough distance in-between.
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
Environmental issues
Both repeaters and pico-BTSs have advantages on environmental issues compared
with macro-cell base stations. Because of their small size and low radiation of
electromagnetic waves, repeaters and pico-BTSs are more suitable for in-building
deployment. They have smaller effect to the health of human being and can be
manufactured with more acceptable appearance. Both of them can be easily and
flexibly installed on the ceiling or wall of buildings.

Security
As more new applications will appear in 3G wireless systems, data security becomes
more important. Special designs are taken by repeaters and pico-BTSs for the
protection of data. As mentioned in Chapter 2, each receiver in the repeater contains a
security circuit for verification. In Chapter 3, we mentioned that the controller node
concept could be adopted to prevent unregistered data interception inside the system.
5.2.1.
Cost Comparison and Analysis
As both repeaters and pico-BTS technologies are solutions for full coverage of mobile
network, their cost comparison is necessary to select the best one suitable to an
application. The cost of these two technologies can be compared with respect to their
installation and operational cost.

Installation cost. At the system level, repeater is very simple (consisting of a receiver,
a transmitter, an amplifier, an isolator and two antennas), compared to pico-BTS
(which has hardware to take care of the physical transmission along with software for
higher layers protocols. Pico-BTS also has added functionalities like power
management, interference cancellation, space diversities, etc., inbuilt to it). All these
makes the pico-BTS much more expensive compared to repeaters.
Repeaters and pico-BTSs have comparable ranges (of the order of few hundred
meters), which tells that the number of repeaters or pico-BTSs required to cover a
particular area is almost same. Apart from all these, pico-BTSs are connected to each
other through high bandwidth cables (which adds to installation cost), whereas
repeaters are mostly connected via wireless links. Repeater network has one CAP to
take care of network functionalities, along with repeaters to provide required
coverage. Hence the installation cost of the repeater network is much less compared
to that of pico-BTS, in most cases. But this cost equation changes when the network
capacity and coverage are beyond some specific values. In such cases the load on
CAP increases making it more complex and hence costly, whereas in case of network
using pico-BTS, each of those operates within their capacity. The cost of this
complex CAP becomes more than the sum total of costs of pico-BTSs and that of the
cables used in the case of pico-BTS based network. The increase in complexity of the
CAP is because of several factors. One such is the complex modulation schemes (like
quadrature amplitude modulation (QAM) or adaptive modulation) used to increase
the capacity of CAP using fixed allocated bandwidth. Also when the capacity of the
repeater network increases, the interference at CAP increases exponentially asking for
more complex interference-cancellation techniques. In such cases, the installation of
repeater network becomes more expensive than the one using pico-BTSs.
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Hence it can be concluded that repeater network has low installation cost compared to
that of pico-BTSs until the network coverage and capacity are below some threshold
value, after which pico-BTS network installation option becomes cheaper. This
threshold value depends on factors like bandwidth available, types of services,
required QoS, and also on cost of repeater, pico-BTS, CAP, and cable.

Operational cost. For a repeater network, part of the operational cost which includes
real estate lease, electricity, hardware maintenance, software maintenance, T1
backhaul etc (as given in Table III) is much less compared to pico-BTS network.
Similarly, there are other components of operational cost, where pico-BTS network
has advantages. One such component is transmission signal power. In case of
repeaters, signal to/from subscribers needs to travel the entire path from the
subscriber to CAP, whereas in case of pico-BTS network, it only travels the path from
the subscriber to the nearest pico-BTS, which implies for same amount of
communication, the repeater network consumes more transmission power compared
to the pico-BTS network. Also when the network capacity is more, the hardware and
software maintenance cost of the CAP becomes comparable to the sum total of
similar cost for all the pico-BTSs. From this it is clear that both these technologies
have operational cost advantages over the other under different network deployment
scenarios.
As both the installation and operational cost for the network using repeaters and picoBTSs are a function of network design parameters, proper calculation must be done to
decide the cost effective solution.
5.2.2.
Comparison and Analysis of Main Markets and Network
Deployment
Both pico-BTS and repeater technologies have many market segments common to each
other. For some applications, either of these two technologies can be used, whereas, for
some others, one of these provides a more cost effective solution compared to the other
one. There are existing and future market segments where only one of the above two
technologies can be used as a solution. The main segments can be categorized as follows:

In-building coverage by mobile network. Market research shows that the demand for
in-building coverage by mobile network is going to increase. If the building to be
covered is of small or of medium size, then repeaters are preferred because of low
cost, no cabling requirement. In such cases, the CAP can be put in the ground floor
and the entire building can be covered by repeaters. As discussed in Chapter 6, as the
size of the building or the required capacity increases (for example in airports,
stadiums, shopping malls etc.) beyond the threshold value, pico-BTS based network
becomes cost-effective. This shows both these technologies have huge market
potential in this segment.

Coverage of shadowed regions in cellular environment. Repeaters are a promising
solution for coverage of shadowed regions in cellular networks, because as the
network capacity is less, there is not need to use a pico-BTS. Also in most of the
cases such regions are straight instead of circular (for example tunnels, parking ramps
and so on), hence using a repeater with directional antenna gives a low-cost solution.
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
Extension of mobile network. Now the demand for including highways, railways into
mobile network is increasing. Apart from that, extension of mobile network across
forests, mountains and also inter-city mobile network is gaining importance. In all
these cases, use of repeaters gives the most cost effective solution.

4G mobile network. For 4G mobile network, where the data rate is going to be of the
order of 10 Mbps, the cell size cannot be more than few hundreds of meters (because
of propagation characteristics of electro-magnetic waves going to be used). Hence,
pico-cells along with pico-BTSs are the proposed solution. Here repeaters can also be
used, but they cannot support frequency reuse across pico-cells, which limit network
capacity. Hence, pico-BTS technology is going to be preferred. This is a huge
potential market for pico-BTS technology.

Extension of satellite network. The satellite network, which is gaining popularity in
entertainment market, can extend its coverage area using repeater technology, also
they can provide mobile access to their service in small areas around the repeater
(which gets connects to the central distribution site via high bandwidth fiber cables).
The above discussion shows that both these technologies are going to see an
increased market for them. But for each one to capture the market of the other one, it has
to improve upon it. Like if the price of pico-BTS becomes less, then it will capture a
substantial portion of the in-building network market. Similarly, if the repeaters are going
to add certain functionalities like space diversity, interference cancellation, power
management, then the market for repeater technology is certainly going to increase.
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6.
Comparison of WLAN and WPBX
6.1.

Comparative Service analysis
WPBX service. A WPBX system is integrated with a wireline PBX to provide mobile
capability to a conventional wireline telephone system. It enables a user to use a
portable handset as a wireless extension to his desktop telephone, thus letting users
keep the same extension number and features as their desktop telephones. It supports
call forwarding to extensions, accessing voice mail, intelligent switching and end-toend transmission.
WPBX also allows the integration of mobile cellular service and local cordless PBX
service. When a user is in his office, his mobile phone serves as personal extension to
the company's PBX. After he leaves office, the phone functions as an ordinary mobile
phone.
In order to realize convergence of telephone with IP data, wireless IP-based systems
running over enterprise LANs should be a technical trend. IEEE 802.11-based
network can integrate wireless voice communications with LAN infrastructure to
support both voice and data communications.

WLAN service. WLAN products have a much wider services. Computers can use
WLAN adapters to form an Ad-Hoc WLAN. Most WLANs are implemented as a
complementary extension to existing wired client server network, in which access
point functions as the server. One or more access points can be used as extensions
points to enlarge such network. Because of the mobility, flexibility and low cost,
WLAN has numerous uses such as home wireless network, enterprise network and
public access.
In many applications, users use WLAN to connect between different devices, in order
to avoid using cables. Such devices include cellular telephone, laptop, PDA, fax
machine and printers. Therefore, it is easily to setup or expand a network of
computers and Internet appliances at home and or office.
With WLAN, people can access data or files stored on servers at remote places,
wherever he physically is. And the access speed is 50-200 times faster than dial-up,
while he does not worry any more about to search for a data port or the long distance
charges.
Wireless packet-switched LAN deals with real-time voice and video services. WLAN
can also provide high-speed multimedia communications among different broadband
core networks such as 3G mobile core networks, ATM networks, IP-based networks,
etc.
A wireless LAN infrastructure can be used for a mobile PBX handset, thus converge
voice and data networks. Voice, audio and video are shared among WLAN-enabled
phones, MP3 players, web cameras, interactive TVs and so on. In this way, WLAN
functions beyond traditional computer networking.
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6.2.
Technical characteristic (capacity and coverage)
comparison and analysis
WLAN and WPBX differ in many technical aspects such as operating frequency, access
technology, interoperability, security, system capacity and area coverage.

Operating frequency.
For WLAN, different frequency bands are utilized for different proposals and
physical working modes. IEEE 802.11b operates in 2.4GHz ISM band. IEEE 802.11a
operates in 5GHz band. Bluetooth network's working frequency is in 2.45 ISM band.
HomeRF network operates in 2.4 GHz ISM band. HiperLAN/2 works in 5.4-5.7 GHz
frequency band.
WPBX systems operate in 800MHz (for narrow-band cellular service), 900MHz (for
in-building systems), 1920-1930MHz (for unlicensed Personal Communications
Services) and 2.4GHz (for integration with LAN).

Access technology.
WPBX systems are mainly based on CDMA, FDMA, and TDMA. While WLAN's
operating modes are much more complex. There are CSMA/CA based WLAN,
ALOHA/ Polling-based LAN, TDMA/CDMA based LAN, or hybrid LAN. IEEE
802.11b can use radio based legacy DSSS, infrared-light based legacy DSSS, or
complementary code keying. IEEE 802.11a uses OFDM. Bluetooth network uses FHCDMA/TDD. HomeRF network's physical layer is based on FH, and it uses 2-FSK/4FSK modulation. HiperLAN/2 network is based on OFDM.

Interoperability.
Different WPBX products have very weak compatibility, even if they work in the
same frequency or they are produced by the same vendor.
Different WLAN products of the same type are compatible to each other, such as
WLAN adapters. Although different types of WLANs using the same ISM band may
cause serious interference to each other, there are some schemes to solve the
coexistence problem between them, such as for IEEE 802.11b and Bluetooth.

Security.
Many WPBX products use FHSS technology to support maximum security against
eavesdropping. Each portable telephone is assigned a unique identification number
registered with the control unit. Only authorized users can access the system.
For WLAN, both 802.11 standards and Bluetooth use keys to encrypt data. Wired
Equivalent Privacy (WEP) technology is an option of 802.11 standard and widely
used by most WLAN products. WEP uses shared keys and a pseudo random number
as an initial vector to encrypt the data. Most current products use 128-bit WEP
encryption.
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
System capacity and area coverage.
WPBX vendors have different series of products suitable for different needs. Such
products could be integrated to a network to maximize the system. For example,
SpectraLink's Link 3000 MCU supports 1000 base stations, 3200 wireless telephones,
and its area coverage is 100 millions square feet.
In a typical Client-Server-based WLAN application, each access point can serve 1550 client devices. The coverage range for a single access point is in the order of 500
feet for indoor environment, and 1000 feet for outdoor environment. Some WLAN
gateway products can reach 25 miles, such as Cisco's Aironet 350 Series.
6.3.
Cost Comparison
Table XVI. Cost comparison of WLAN and WPBX (unit: $)
WLAN
WPBX
Access Point
500 - 1,000
Base Station
1,000 - 2,000
Network Card
100 - 200
Handset
500 - 700
Radio Controller
2,000 - 4,000
A typical WLAN system consists of access points and network adapter cards. An access
point costs around $500 - $1,000, and a network adapter card costs around $100 - $200.
Typically, an access point can serve about 15 - 20 users at the same time. Thus, if we
assume that we construct a WLAN system composed of 20 users, it will cost around
$2,500 - $5,000. A typical WPBX system is composed of radio controllers, base stations,
and wireless handsets. A radio controller costs around $2,000 - $4,000. A base station
costs around $1,000 - $2,000, and a wireless handset costs around $500 - $700. Thus, if it
is assumed that a WPBX system serving 20 users is constructed, it will cost around
$13,000 - $20,000. Table XVI shows the cost comparison between WLAN and WPBX.
From this, we can know that a WLAN system is cost effective compared to a WPBX
system.
The initial installation cost of a WLAN system is much cheaper than that of a
WPBX system as shown above. Moreover, once installed, the WLAN system has less
management expenses than the WPBX system. A WPBX system cannot function as a
stand-alone PBX. It works together with conventional PBX systems. Thus, it involves
more installation and operational costs than the WLAN system. Hence, the overall cost
including the installation and the operational costs of the WLAN system is much cheaper
than that of the WPBX system.
6.4.
Markets and Network Deployment Comparison
There is an increasing demand for WLAN technology. The WLAN market is mainly
being driven by the growing demand for bandwidth from portable PCs to Web browser
and corporate applications. WLANs provide high-speed services that make access to
email and corporate applications feasible. The market for WLAN system that is intended
for PC connectivity will be slightly less than $1.4 billion in 2001. The market is expected
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to grow to $3.2 billion in 2005. Some of the WLAN market opportunities include the
following:

Use of WLAN technology to connect consumer goods such as set-top box, etc.

Public access WLANs could remove the need for data connectivity provided by 3G
cellular and packet data networks, therefore grabbing the market chance for public
network access.

The advantages of 5GHz products such as increased bandwidth, QoS and reduced
interference could force customers to go without 2.4GHz compatibility. This would
shift the market away from less costly 2.4GHz-capable solutions to relatively more
costly but cost-effective 5GHz solutions.
WLAN market development and growth has been delayed by overflow of
standards, which confused potential customers. Moreover, decisions were delayed while
market players waited for new standards. Supported by the interoperability testing
services of the Wireless Ethernet Compatibility Alliance (WECA), the IEEE 802.11
standards are emerging as the leaders. The technology is expected to continue to evolve.
Products complying with the 802.11a standard will be available during the first half of
2002, boosting maximum data rates from the 802.11b standard's 11 Mbps to 54 Mbps. By
using the broader 5.0GHz unlicensed band, 802.11a will also address many of the
spectrum congestion issues in the 2.4GHz band used by 802.11b.
The wireless options for the PBX have not shown much growth even though
WPBXs have been on the market for almost 10 years. Less than 5% of the new PBX
system shipments are WPBX. Some of the several reasons for the relatively low shipment
for WPBX are pricing, technology, customer awareness and education. Among these, the
main reason is the pricing problem. The cost per user for a WPBX system is expensive.
Sometimes it is three times of a conventional wire-line desktop phone. It is even more
expensive than that of WLAN system as shown above. However, since in-building
wireless communications is growing rapidly, lots of opportunities exist for manufacturers
with innovative products and applications. Customers want cordless telephones, full
roaming, and seamless handoff while they are receiving calls. Multiple product lines,
broader distribution channels, and increased roaming capability are the important issues
concerning wireless vendors' current market strategies.
The market for WPBXs is changing rapidly. It is expected that the market will
grow to almost $840 million by 2005, over a factor of three to one from the base year of
2000.
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7.
7.1.
Comparison of Pico-BTS and WLAN/WPBX
Comparative Service Analysis
In order to provide low cost and high traffic rate wireless services for local areas, several
wireless systems have been developed independently. For example, pico-BTS is used to
enhance the traditional cellular system in the indoor environments. By using low-cost
pico-BTS, higher capacity and services with better quality can be supported in buildings.
WLAN is another technique to provide high speed wireless services to local area users.
For a conventional wireline telephone system, WPBX is used to provide the mobile
capability to end users in a local area such as buildings.
Several services can be supported by pico-BTS, WLAN, and WPBX. Among
them, some are the same, while others are different.
As investigated in Chapter 3, pico-BTS is a type of cellular system, and thus, it is
a complimentary part of the wireless cellular system. All the existing services in the 2.5G
and 3G cellular systems can be supported in a pico-BTS system. However, since higher
capacity can be offered by a cell in a pico-BTS system, larger traffic rate than that in
2.5G and 3G systems can be provided by pico-BTS systems. In this sense, pico-BTS is
closer to the objective of the next generation wireless communication system. However,
to really achieve the goal of the next generation wireless communication system, efficient
protocols to support multimedia services need to be developed. Moreover, pico-BTS has
much smaller cell than the conventional cells in 2.5G and 3G system, which provides a
possibility of developing more precise location-aware services. Pico-BTS can be
integrated with 2.5G and 3G cellular systems in a seamless way, because it is actually the
same type of system as conventional cellular network. However, to access Internet via
pico-BTS does not have a direct solution. It must depend on the conventional cellular
system that is connected to pico-BTS. If the cellular system connected to pico-BTS is a
2G network, Internet access is not available. When the pico-BTS is connected to 2.5G or
3G, Internet access is supported.
In contrast, WLAN is a network that can be totally independent from other
networks, as descried in Chapter 4. Current WLAN systems can provide much higher
traffic rate than pico-BTS system. For example, the traffic rate of IEEE 802.11b can be as
high as 11 Mbps, while a pico-BTS is almost impossible to deliver such a high traffic
rate. However, in the same situation as pico-BTS system, new protocols such as MAC
need to be developed in order to really support multimedia services in WLAN. For
example, most of the existing WLANs such as IEEE 802.11 series, HomeRF, and
Bluetooth are very weak in QoS guarantees for real-time services, although the
transmission rate of data applications can be very high. Some WLANs such as HomeRF
can be connected to PSTN so that voice communication can be smoothly supported,
while the WLANs such as IEEE 802.11 and Bluetooth do not have a good solution to
deliver voice service. Normally, voice over IP should be used if voice service needs to be
supported. However, Internet over WLAN is an obvious solution, because data services
are supported in all WLANs. It is not so apparent to integrate WLANs with 2G or 2.5G
cellular systems because WLANs are purely packet-based network. However, since 3G
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and the next generation cellular systems are also purely packet-based, the integration of
such WLANs with cellular systems will be seamless, which is one of the objectives of the
next generation communication system. WLAN can be ad-hoc or infrastructure-based, so
network topology is very flexible. However, due to this flexibility, to provide locationaware service in a WLAN becomes more challenging. Another severe issue still exist in
WLAN is interference. Although co-channel interference also exists in pico-BTS system,
devices in pico-BTS systems do not experience interference from other devices working
in the same frequency band. However, a WLAN device experiences such interference,
which significantly degrades the performance of WLANs.
As pointed out in Chapter 5, current WPBX can only support voice service with
either on-site or off-site mobility. Thus, data applications and multimedia services cannot
be provided in a WPBX system. Base station is required in a WPBX system, so WPBX is
also an infrastructure-based network. Interference could be an issue if WPBX works in an
unlicensed frequency band. Location-aware service is difficult to provide in a WPBX,
because WPBX is connected to PSTN instead of a cellular system.
Features and services provided by pico-BTS, WLANs, and WPBX are compared
in Table XVII.
Table XVII. Comparison of the features and services of pico-BTS and WLAN
Features or Services
Data Rate
Voice Service
Pico-BTS
Medium
Supported
Data Applications
Depending on the
conventional
cellular s
Supported in the
future
Supported
Multimedia Services
Support
Location-Aware
Service Provision
Integration with
Cellular Systems
Network Topology
Interference
WLAN
High
Supported in some
WLANs
Supported
WPBX
Low
Supported
Not supported
Supported in some
WLANs
To be developed
Not supported
Seamless
To be developed
Infeasible
Infrastructure
Ad-hoc or
infrastructure
Severe
Infrastructure
Low
Not supported
Severe in unlicensed
In the industrial practice, hybrid networks that combine pico-BTS with WLAN or
WLAN with WPBX exist. Such hybrid networks hold features of both systems. For
example, when WLAN is integrated with WPBX, both voice and data applications can be
supported with good quality. In the hybrid network, if WPBX is used in an area with
severe interference that could be experienced by a WLAN, the interference issue of
WLAN can be improved.
In the next generation cellular system, the network is packet-oriented. Thus,
integrating WLAN with the cellular system is straightforward. However, since pico-BTS
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is also used for indoor environments, it is more advantageous to integrate WLANs with
pico-BTS system first and then the outdoor cellular systems are connected through picoBTS.
7.2.
Technical Characteristics Comparison and Analysis
The technical characteristics of the pico-BTSs, the WPBXs and various kinds of WLANs
are compared below.

Standards
Different types of WLANs are standardized by different bodies. IEEE 802.11 is
standardized by IEEE, and some working groups still continue working on the
standardization process. Bluetooth standardization is driven by the Bluetooth Special
Interest Group, and it is not complete yet. The HomeRF Working Group is about to
finalize the standards for the HomeRF and SWAP networks. The standards for the
HiperLAN/2 networks are set by ETSI. The ETSI organization also sets the standards
for the pico-BTS networks.

Physical and MAC layers
IEEE 802.11 uses direct sequence spread spectrum, infrared and OFDM technologies
in the physical network. Its MAC layer is based on CSMA/CA. The MAC layer in
Bluetooth uses frequency hopping CDMA based on polling or Aloha protocol. In
HomeRF, the MAC layer is TDMA-based for isochronous services, and CSMA/CAbased for asynchronous services. The MAC layer in HiperLAN/2 is TDMA/TDDbased. The pico-BTS system in 2G networks is designed mainly for voice, and its
MAC layer is the same as the network it is integrated with. WPBX systems are voiceonly networks and their MAC layers are determined by the access technologies.

Frequency bands
IEEE 802.11 systems operate at the 2.4 GHz, 5 GHz and Infrared frequency bands.
Bluetooth operates at the 2.45 GHz ISM band. The frequency bands for HomeRF and
HiperLAN/2 networks are at 2.4 GHz ISM and 5.4-5.7 GHz. Pico-BTS systems
operate at 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz, depending on the type.
The WPBX systems operate at 800 MHz, 900 MHz, 1920-1930 MHz U-PCS, and 2.4
GHz bands.

Infrastructure and organization
IEEE 802.11 and HomeRF systems work in both cellular and ad-hoc modes. In the
cellular mode, each mobile terminal communicates with an access point. In the adhoc mode, the communication is peer-to-peer. In Bluetooth networks, there is a
centralized organization; one master node and several slave nodes exist in each
piconet. HiperLAN and WPBX systems have cellular infrastructures. The pico-BTS
systems are also cellular by nature since they are part of larger cellular networks.
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
QoS support
IEEE 802.11 systems support only priorities for different types of traffic. However,
work is under way to enhance the QoS capability of IEEE 802.11 systems. Bluetooth,
HomeRF, HiperLAN/2, and WPBX systems provide do not support QoS
specifications. Pico-BTS systems can provide limited QoS support, but extensive
research is required to improve it.

Maximum transfer rate
The transmission rate of IEEE 802.11 systems ranges from 1 Mbps to 54 Mbps,
depending on the type. HomeRF systems provide a transmission rate up to 1 Mbps
while it is lower than 1 Mbps for Bluetooth. HiperLAN/2 systems provide a
transmission rate of 54 Mbps at the physical layer, but it is only 32 Mbps at the
network layer. The transmission rate of a pico-BTS system is determined by the
cellular network it integrates with. WPBX systems are intended only as extension of
the desktop telephones to provide voice communication, and their transmission rates
are very low.

Integration with other networks
The integration of the WLAN systems requires more improvement. Since WLANs
are considered to be a part of the next generation systems, there is increasing research
on this issue. The pico-BTS systems are already part of larger cellular systems, and
they are fully integrated. The WPBX systems, except those that operate at U-PCS
frequency band, can be integrated with cellular systems.
7.3.
Cost Comparison and Analysis
Costs of pico-BTS, WLAN, and WPBX have been analyzed in Chapters 3, 4, and 5,
respectively. Here a more comprehensive comparison is performed again based on the
results in Chapters 3, 4, and 5.
To deploy and operate a wireless network in an indoor or local area environment,
the costs are generally determined by the following important factors:

Deployment costs. This type of costs is related to several other factors such as
frequency planning, network design, and deployment difficulty.

Equipment costs. Such type of costs is determined by the number of devices and the
prices of these devices.

Operation costs. Operation of a network includes configuration of networks, service
provision and pricing, maintenance and management of network, and so on.
Based on these factors, the costs of pico-BTS, WLAN, and WPBX are compared
in Table XVIII.
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Table XVIII. Comparison of the costs of pico-BTS, WLAN, and WPBX
Cost Index
Frequency Planning
Network Design
Pico-BTS
High
High Complexity
WLAN
Low
Low
Deployment
Complexity
Number of Base
Stations
Price of Base
Stations
Price of Gateway
Price of Mobile
Terminals
High
Low
WPBX
Medium
Medium
Complexity
Medium
Medium
Low
Medium
Expensive
Low
Low
Expensive
Low
Low
Medium
Expensive
Low
High Complexity
Low Complexity
Medium
Complexity
Medium
Complexity
Simple
Network
Configuration |
High Complexity |
Low Complexity |
Simple
Simple
High
| Network
Configuration
Network
Maintenance
Service Provision
and Pricing
As shown in Table XVIII, the WLAN is much economical than the other two in
terms of network deployment costs. The reason is that WLAN is a relative independent
network and works in a public ISM frequency band. Because the techniques of base
stations (or access points) of a WLAN is simpler compared with pico-BTS or WPBX, the
price of WLAN base station is generally cheaper. The same reason causes the price
difference in gateways of pico-BTS, WLAN, and WPBX. Since WLAN is very flexible
in network topology, the network configuration of WLAN is simpler. The same reason
can be applied to the different costs in network maintenance and service provision and
pricing. From Table XVIII, WLAN is shown to be much more advantageous than the
other two options for wireless networks in local areas. However, it should be pointed out
that, when deploying a wireless network, cost is not the only criterion to decide which
option can be used. Actually, the features and services are also important aspects that
concern network designer and service provider. In other words, the comparisons of costs
in this subsection should be considered together with the comparisons of network features
and services in Subsection 7.1.
7.4.
Comparisons and Analysis of Main Target Markets and
Network Deployments
Pico-BTS provides low-cost and higher capacity to users in an indoor environment. It
also provides a bridge between WLANs and 3G cellular networks. Thus, pico-BTS has
been widely accepted. Its market is steadily increasing. For example, based on pico-BTS,
cdmaOne is enabled to compete with TDMA and GSM networks.
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The market of WLAN is increasing more than predicted. WLAN is going to exist
in all kinds of local area environments such as homes, offices, educational institutes,
warehouses, health centers, hotels, airports, and many more. Thus, the market penetration
of WLAN is promising.
However, WPBX does not hold a huge market. Currently, its market is just a
small percentage of the whole PBX markets. Its capability to penetrate the market of
other wireless products is not strong, because its simple function cannot satisfy the everincreasing demands on the new services of wireless communication. However, since
WPBX can be integrated with other networks, it will continue to hold some percentages
of market for wireless products. For example, WPBX can be integrated with WLANs so
that the hybrid networks can enhance the performance of both networks, which enhances
the market penetration capability of WPBX.
The target market and network deployment of pico-BTS, WLAN, and WPBX are
compared in Table XIX. In such a table, the following factors that affect the market and
network deployments are considered:

Motivation. This factor is determined by the functionality, technology advantages,
costs, and customer needs.

Current market percentage. Although a higher current market percentage cannot
guarantee a big future market, it reflects the actual needs from users.

Network deployments. This reflects the usage of a wireless solution. If a wireless
solution can be applied to various environments, it is expected to have a huge market.

Market development. This means if a market is increasing, decreasing, or stable.

Market penetration capability. This is a very important factor that determines the
future of a wireless solution. If the market penetration capability of a wireless
solution is high, the market must be very promising.
Table XIX. Comparison of the markets of pico-BTS, WLAN, and WPBX
Market Index
Motivation
Current Market
Percentage
Network
Deployments
Market
Development
Market Penetration
Capability
Pico-BTS
Moderate
Medium
WLAN
Strong
High
WPBX
Weak
Low
Buildings under coverage
of conventional cellular
systems
Steadily increasing
All local areas
Buildings with PBX
Increasing fast
Stable
Moderate
Strong
Weak
From Table XIX, we know that WLAN is going to be the wireless solution with
much bigger market than the other two solutions. However, pico-BTS will also hold a big
percentage of market. Both pico-BTS and WLANs will be an important wireless solution
in the next generation wireless networks. They can together as a hybrid network. In
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contrast, WPBX does not have a promising future market unless some innovative
technologies are developed to enhance its functionality. However, it is going to exist for a
certain period to provide the wireless voice services in a conventional telephone system.
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8.
In-Building Deployment
8.1.
Taking advantage of technological evolution and meeting
customer demands
Most wireless system venders and service providers declare their supports and evolutions
to 3G wireless systems. While they may take different technique approaches.
Europe and Japan support WCDMA system, which is a great improvement from
GSM in terms of data delivery. Currently, the feature set of WCDMA has evolved from
R99, through R00 to R01. NTT DoCoMo has launched its WCDMA system in the end of
this year, which is a R99 version.
United States and Korea prefer the cdma2000 system, which is based on IS-95.
But they are in different situations now. While Korea has the highest concentration of IS95 users, the United States faces the problem of several incompatible systems in use.
Even AT&T uses WCDMA system.
China’s TD-SCDMA is also proved by ITU as an IMT-2000 standard, though it
has a narrower rate of 1.28 Mbps. In current Chinese market, two totally different service
providers exist. China Mobile, with its 67.5 million GSM users, ranks number one in the
Chinese wireless market. It also supports GPRS service. The second player, China
Unicom, will launch the largest CDMA network all over the world on Dec 31 2001. The
first deployment phase will have 15.15 million users, 188 switches and 14,500 base
stations, based on an enhanced I-95A version. It plans to increase its capacity to 50
million users in 2003. One problem is the incompatibility of 4 kinds of different UIM
card in use now.
At the same time, China Unicom will launch its first CDMA-1X commercial
testing network covering 7 big cities including Beijing and Shanghai. Such network could
be upgraded onto 3G system smoothly.
The interoperability between CDMA and GSM is a big issue. The CDMA
network in Singapore failed recently shows the importance of this problem. Now Korean
Telecom delivers a GSM-CDMA two-mode mobile phone which will support GSM’s
SIM card to be used in Korea. It may be a potential solution. Another approach is to have
a traffic control function that is able to handle all spectrums allocated by the two systems
as one. Adaptive Traffic Control ensures full utilization of the combined spectrum and
resources with a seamless handover, and transfer of connections between the GSM and
CDMA systems.
No matter what kinds of technology to be used, successful service provider should
provide customers with the following services:

Greater coverage

High-speed rates

Scalable and manageable bandwidth

Enable new (high-end) services (and keep running the good old ones)
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
Service differentiation

Smooth deployment and low maintenance

Interoperable systems

Plug & Play

Extends the local area network

Freedom to access the corporate network

Comparable to those of wired networks

Secure access to important information (e-mail, corporate data, Internet)
More and more users prefer an integrated wireless network that could integrate
different wireless systems together and use them seamlessly. Therefore, successful
operators should offer a seamless handover between 3G and WLANs.
Currently, physical layer technologies for different wireless systems are
incompatible. Each of them occupies a different frequency band and their physical
interfaces are totally different. However, competitive service providers should provide
customer integrated service among different wireless networks, such as WCDMA cellular
systems, high speed WLANs, and home wireless networks. To achieve this goal, some
companies and research centers are developing novice techniques to produce a seamless
multitier network interface. A Multitier Network Interface Card (mNIC) for service
continuity is a hot topic now. It is a multi-tier network interface card which could be
reprogrammable to different physical and network-layer standards [100]. Researchers are
now developing a reconfigurable testbed and a prototype. DSP processors, custom VLSI
ASICs and FPGA techniques are involved.
In industry practice, another innovative concept is Always Best Connected
(ABC). This concept is given by Ericsson [98]. It provides operator a multi-access
solution that can integrate with CDMA, WLAN and Bluetooth. In this scenario, the
CDMA system covers a wide area network, while WLAN supports services in smaller
hot spots such as airports, and Bluetooth is used as a cost-effective access technology for
a PAN.
IN Ericsson’s solution, Bluetooth is used as the common interface technology for
all types of access. The different kinds of access should be identified and the optimal
access should be chosen automatically, without user’s interaction. Ericsson's CDMA2000
1xEV demonstration has been implemented in Nov 2001.
However, since Bluetooth has a relatively lower bit rate (no more than 1Mbps)
and its weak support for QoS, especially in real time communication such as video, some
other research institute may choose other access technology as the common interface.
The Broadband and Wireless Network Laboratory (BWN) of Georgia Tech will select
WLAN as the common interface in its Next Generation Wireless Network project.
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8.2.
Network deployment scenario (Technology, Market,
Architecture, Implementation Phases, schedule,
Resource estimates)
Since the customers have various requirements for their specific network environment
and needs, service providers should offer them different network deployment
accordingly, considering the network capacity, price, connectivity, and scale, etc.
8.2.1.
Wireless PBX System deployment for corporate
In a corporate which have a great needs for its employees to access telephone in building
frequently, it should have a wireless PBX system deployment. Wireless PBX is a mobile
communication system which connects the outside PSTN and the inner wireless base
stations. The wireless handsets can be used as extension telephones, so users can call
anywhere and anytime under the coverage. The lower charge is also attractive, because
the WPBX system is belong to run in the corporation’s own mobile communication
network, no extra charge is required. Besides, this system provides the company
broadcasting function, which is a necessary requirement in big buildings and malls.
Figure 29 shows an example fulfilling the needs of small size enterprises and
home-offices [94]. It should provide the following features:

Reliable wireless mobility

User-friendly features

System administration

Plug-and-go installation

Flexible relocation for dynamic workplace

Both stand-alone system, and being able to be connected to an existing corded PBX

Support maximum security against eavesdropping
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Figure 29. A wireless PBX system for small size corporate
The system consists of three major components: the Master Base station, the
Remote Base station (RBS), and the Wireless Handset. The diameter of each Remote
Base station’s cell coverage is about one kilometer, and whole system coverage is three
or more square kilometers. Typically, it is a multi-cell system supports four to eight
analog trunk lines, 16 simultaneous speech connections and 70 wireless handsets.
8.2.2.
WLAN internetworking with Wired Network
Some vendors provide WLAN 11 Mbps system deployment architecture shown in Figure
30, such as Ericsson [95].
Wireless LAN Guard will provide very high security protection. Besides, by using
authentication and encryption process with 128 bit encryption, each user will have safe
pre-shared keys and public certificate. The Wireless LAN Guard also functions as a
central monitor from which one people can configure, track the traffic, and manage the
whole system. A WEB based configuration of Access Points offers more convenience.
The site management enables users to can move from one location to another and connect
to the network.
By using a Virtual Private Network (VPN) service, the users could access the
enterprise network. Service providers may also extend the service area for the enterprise
user to certain public areas.
121
Figure 30. WLAN 11Mbps system architecture
8.2.3.
Unified 3G Wireless Network
In the future, customers may prefer a unified wireless 3G wireless network that integrates
all the wireless technologies together, and provide the customers a complete, seamless
and secure service. Unified 3G Wireless Network shown in Figure 31 will provide:

Flexibility for Internet-based Data & Multimedia Services

Bandwidth on Demand

Lower Cost Than 2G for “Basic” Services

Plus New Service Capabilities

Significantly Improved Operational Efficiency (esp. Capacity/Spectrum Efficiency)

Service Transparency/Global Roaming
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Figure 31. Unified 3G wireless network
The core of the network is a Multi-service IP network. Various services will be
supported including provisioning, PBX, VoIP, Value added, Billing, Settlements, Call
and Session control, Multimedia, etc. Users can select WLAN, or ADSL to access the
core network. Besides, both WCDMA and GSM systems could be supported
simultaneously.
8.2.4.
Complementary Technologies of cdma2000 and 802.11
QUALCOMM provides another prospective network deployment approach for inbuilding wireless communication [97]. This approach will provide benefits for ender
users, service operators and vendors. End users benefit from seamless wireless Internet
services, and such service will be affordable and runs everywhere. Operators function as
the preferred wireless Internet providers. Device Vendors should provide different and
utilities to fulfill the specific requirements for end users and operators.
Enterprise WLAN’s coverage should be included and integrated into the
WCDMA/cdma2000 coverage. In this coverage, laptops, PDAs and cell phones should be
supported everywhere at anytime. In order to achieve this deployment, two more
requirements should be fulfilled:

Dual Mode Laptop/PDAs that work both on WCDMA/cdma2000 and WLAN

Integrated Authentication mechanism with the Enterprise Wired LAN
123
There are some additional benefits for this deployment Compared to other WLAN
approaches, especially for enterprise:

Portability within the Enterprise

Leveraging existing Enterprise LAN

Direct access to information on the Intranet

Easy maintenance with existing LAN management system

Same security mechanisms as wired LAN

No monthly service fees

WLAN owned and operated by Office

Free use of unlicensed spectrum

Sufficient coverage with LAN

Employees are concentrated in a few areas of Enterprise when away from desk

LANs can provide sufficient coverage within Enterprise
There are may be three kinds of network deployment scenarios for end users and
service providers. Providers could select one to fulfill the users’ specific needs.

WLAN operators are different from the WCDMA/cdma2000 Operator and WLAN
operators compete with each other. This is not a long-term proposition. The main
reasons come from the complicated charge fees and the difficulties to integrate.
There may more than 1 WLAN operators to provide service. Each WLAN location
has its own monthly backhaul costs, and each WLAN operator has its own billing,
and authentication scheme. WCDMA/cdma2000 Operator will also feel to setup
roaming agreements with numerous independent WLAN operators.

WCDMA/Cdma2000 Operator and one WLAN operator are both offering commercial
service but compete with each other. WCDMA/cdma2000 operator will dominate in
this battle because their ubiquitous coverage advantage is overwhelming. Each
WLAN location has a monthly backhaul cost associated with it.

WCDMA/cdma2000 operator provides both CDMA and WLAN Services. This
scenario has integrated billing and authentication schemes. End users may find this
service is easily to use, and the charge will be unified and cheaper. Such a
combination enables end users to use wireless data everywhere easily. End user does
not have to know or worry about which air link is being used. WCDMA/Cdma2000
operator may own the WLAN, or wholesales from one other WLAN Operator. For
the latter, the advantage is that WCDMA/cmda2000 operator does not worry about
operation and maintenance of the WLAN.
8.2.5.
VPN security for Wireless Communication
When choosing network deployment schemes, each corporate consider the security as
one of the highest requirements. Currently, the combination of VPN (IPSec) and 802.11
is an ideal solution for wireless networking security needs. In such a scenario, the
124
wireless access points do not need WEP encryption themselves. All the security
considerations are carried out by the VPN. The VPN servers provide encapsulation,
authentication and full encryption over the LAN. To the end users, they will have a fully
secure access to their network resource as if the data transferred ‘transparently’. The VPN
approach is flexible enough to be used in a variety of different scenarios. In each
scenario, the user has a same login interface and procedure (shown in Figure 32).
Figure 32. VPN (IPSec) provides wireless network security
8.2.6.
HiperLAN/2 deployment for Corporate LAN
Since HiperLAN/2 have good support for QoS, many corporate will select such network
deployment to support real-time wireless communication. Figure 33 shows an example.
In this scenario, the corporate network is built on ethernet LAN and IP routers. Then, a
HiperLAN/2 network is used as the last segment between the mobile terminals and the
network/LAN. In subnet A, the HiperLAN/2 network supports mobility within the same
LAN/subnet. However, when the terminal is moving between different subnets (From A
to B), the handover should be handled by a layer above HiperLAN/2 [93].
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Figure 33. HiperLAN/2 used in a corporate network
HiperLAN/2 can be used as an alternative access technology to a 3rd generation
cellular network, especially to provide wireless coverage for hot spots. The combination
of using HiperLAN/2 in hot spots and using WCDMA technology for wide area is
potential approach. In this way, a user can benefit from a high-performance network
wherever it is feasible to deploy HiperLAN/2 and use W-CDMA elsewhere. Handovers
can be achieved between the two types of access networks.
126
9.
Conclusion
Most wireless communication operators declare they have plans to involve to 3G wireless
systems and will provide the customers the best wireless access from anywhere at
anytime, though they may take different technique standards. However, what the users
want most is to have a mergence of the wireless communication services that they get
from different operators currently. The market needs for integration with Bluetooth,
WLAN and cellular system is increasing rapidly, thus brings a great opportunity for those
competitive service providers who will have the strategy to integrate various wireless
technologies, and provide end users a completed, seamless service. Today’s high-rate
wireless communication technologies could enable the operators to achieve their
strategies.
Some key issues should be handled carefully when service providers offer
network deployment to their customers. Among them, the interoperability between
different wireless network systems is a key issue requiring further breakthrough from
novice technologies. The mNIC technology and Always Best Connected concept may be
the potential approaches. Compared to fixed network, the security problem is another
important and sensitive issue requiring more consideration when implementing network
deployment. In WLAN scenario, most providers use encrypted WEP technologies. In
practical use, the combination of VPN and IPSec is an ideal solution. To achieve the
high-rate wireless network integration and support real-time and multimedia wireless
communications with guaranteed QoS, many new modifications should be taken for
wireless repeaters, Pico-BTS, and WPABX devices.
Various vendors and research institute have different technology standards to
compete with each other. But the end users need a ‘transparent’ integration of those
detailed technologies. Besides, since different countries’ operators may take different
approach to involve to the 3G wireless systems, how to handover among different
systems should be a great issue.
Further more, since the needs from various enterprises and end users are quite
different from each other, the service providers should prepare various network
deployments for them accordingly. Lots of issues need to be considered including the
network capacity, the connectivity to wired network, the QoS, the security, the price and
the performance.
A competitive solution should provide seamless end-to-end connectivity from
mobile users to wired ones. A web-based, centralized network management is another
consideration most customers want. The more usages brought to customers, the more
revenue you get.
In short, the successful operators will be those who have strategy to deliver
mobile data through high speed 3G networks, and provide end users seamless, guaranteed
and affordable wireless access everywhere, anytime.
127
10. References
[1]
H. Newton and R. Horak, Newton's Telecom Dictionary.
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