Comparison of Mobile WiMAX and
HSDPA
KOLBRUN JOHANNA RUNARSDOTTIR
Master of Science Thesis
Stockholm, Sweden 2008
Comparison of Mobile WiMAX and
HSDPA
KOLBRUN JOHANNA RUNARSDOTTIR
Master of Science Thesis performed at
the Radio Communication Systems Group, KTH.
June 2008
Examiner: Professor Ben Slimane
KTH School of Information and Communications Technology (ICT)
Department of Communication Systems (CoS)
CoS/RCS 2008-10
c Kolbrun Johanna Runarsdottir, June 2008
Tryck: Universitetsservice AB
Abstract
HSDPA and Mobile WiMAX are high speed mobile technologies with different
backgrounds. HSDPA is a data enhancement for a voice-centric 3GPP system while
WiMAX is data-centric broadband technology that has an added feature of mobility.
To investigate how the technical advantages and limitations of those technologies affect
their feasibility as investment choices, first a general overview and comparison is given.
Thereafter the deployment cost and operating cost over 10 years is estimated for the case
of a new market entrant. This is done for the specific case of the city of Reykjavík.
Radio planning assumptions and link budget calculations are made. This affects the
network dimensioning, which in turn determines the infrastructure cost.
As Reykjavík is a city with few inhabitants but a large area, coverage had more affect on
the infrastructure cost than the capacity. Another factor that made the networks less
sensitive to capacity limitations was that the system model did not consider interference.
The 60% longer radius of HSDPA gave it an advantage in economic feasibility while 70
% higher throughput for Mobile WiMAX did not give any economic advantage under the
considered assumptions.
If the cell radius of the two technologies is set to be of the same length the outcome of
the business cases is very similar. Variations in cell radius has a big impact on the NPV
and IRR of both business cases while changing the average channel throughput has a
little impact.
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1. Introduction
2. Overview and comparison of mobile WiMAX and HSDPA
2.1.1 Background
2.1.3.Other features of Mobile WiMAX
2.2.1 Background
3.1.4 Link Budget
4. Techno economic analysis
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5
List of tables
Table 1. MCS levels and DL PHY data rates in Mobile WiMAX [5] ............................. 17
Table 2. Some features of W-CDMA ............................................................................... 25
Table 3. HSDPA terminal capability categories [15] ...................................................... 30
Table 4. Peak data rates with number of codes fixed at 15 [15],[10] .............................. 30
Table 5. Differences between WCDMA (R´99) and HSDPA ......................................... 32
Table 6. Comparison of some of the features of Mobile WiMAX and HSDPA ............. 36
Table 7. Model Parameters. ............................................................................................. 43
Table 8. Uplink link budget ............................................................................................. 45
Table 9. Downlink link budget ........................................................................................ 46
Table 10. Common system parameters for HSDPA and Mobile WiMAX...................... 49
Table 11. System specific parameters.............................................................................. 49
Table 12. SINR for different MCS levels, IEEE 802.16e [24], [31] ............................... 51
Table 13. HSDPA Rx sensitivity for different MCS levels. [27] .................................... 52
Table 14. Rx sensitivity for mobile WiMAX (5 and 10 MHz). [24], [38], [31]............. 52
Table 15. Cell radius, for HSDPA and Mobile WiMAX (5 MHz and 10 MHz)............. 53
Table 16. Distribution of modulation and coding schemes, HSDPA. ............................. 54
Table 17. Distribution of modulation and coding schemes, mobile WiMAX 10 MHz... 55
Table 18. Distribution of modulation and coding schemes, mobile WiMAX, 5 MHz.... 56
Table 19. WiMAX, peak data rates for different modulation and coding schemes.......... 56
Table 20. HSDPA peak data rates for different modulation and coding schemes........... 56
Table 21. A prediction of the mobile broadband market ................................................. 59
Table 22. Installation and site cost................................................................................... 60
Table 23. ARPU (Average Revenue/User) and data rate for 3 subscription types. [4] .. 60
Table 24. Cell radius and average throughput ................................................................. 61
Table 25. Nr. of BSs needed to fulfill coverage and capacity requirements. ................... 62
Table 26.Required investment capital, NPV and IRR for Mobile WiMAX 10 MHz ...... 65
Table 27.Required investment capital, NPV and IRR for Mobile WiMAX 5 MHz ........ 65
Table 28.Required investment capital, NPV and IRR for HSDPA .................................. 65
Table 29.Comparison of WiMAX with 5 MHz bandwidth and 10 MHz bandwidth ....... 67
Table 30. Comparison of HSDPA and mobile WiMAX (5 MHz BW)............................ 68
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List of figures
Figure 1. The layers of the OSI model, and the Data Link sublayers, LLC and MAC. .. 15
Figure 2. Network Architecture of Mobile WiMAX ........................................................ 20
Figure 3. UMTS network architecture ............................................................................. 33
Figure 4. Distribution of MCS, HSDPA ........................................................................... 55
Figure 5. Distribution of MSC for WiMAX 10 MHz....................................................... 55
Figure 6. Distribution of MCS for mobile WiMAX 5 MHz............................................ 56
Figure 7. Example of a cash balance curve...................................................................... 64
Figure 8. Cash balance curve for mobile WiMAX 10 MHz............................................ 66
Figure 9. Cash balance curve for mobile WiMAX 5 MHz.............................................. 66
Figure 10. Cash balance curve for HSDPA ..................................................................... 66
Figure 11.Sensitivity on cell radius. ................................................................................. 69
Figure 12. Sensitivity on channel throughput .................................................................. 70
Figure 13. Sensitivity on penetration levels..................................................................... 71
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List of abbreviations
AMC – Adaptive Modulation and Coding
ARPU – Average Revenue Per User
BS (BST) – Base Station
BW – Bandwidth
CAPEX – Capital Expenditures
CPE – Customer Premises Equipment
dB – Decibel
dBi – dB isotropic
dBm – dB milliwatt
DL – Down Link
DVB– Digital Video Broadcasting
EIRP – Effective Isotropic Radiated Power
FDD – Frequency Division Duplex
H-ARQ – Hybrid Automatic Repeat Request
HSDPA – High-Speed Downlink Packet Access
IEEE – Institute of Electrical and Electronics Engineers
IP– Internet Protocol
IRR – Internal Rate of Return
LOS – Line of Sight
MAPL – Maximum Allowable Path Loss
MCS – Modulation and Coding Scheme
MMS – Multimedia Messaging Service
MS – Mobile Station
NLOS – None Line of Sight
NPV – Net Present Value
OFDM – Orthogonal Frequency Division Multiplexing
OFDMA – Orthogonal Frequency Division Multiple Access
OPEX – Operative Expenditures
PDA – Personal Digital Assistant
QAM – Quadrature Amplitude Modulation
QoS – Quality of Service
QPSK – Quadrature Phase Shift Keying
SNR – Signal to Noise Ratio
TDD– Time Division Duplex
UL – Up Link
UMTS – Universal Mobile Telecommunications System
VoIP – Voice over Internet Protocol
WiMAX – Worldwide Interoperability for Microwave Access
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1. Introduction
1.1. Síminn and the Icelandic telecom market
The work in this thesis has been requested by the Icelandic Telecom company, Síminn
1
.
Síminn has carried out studies on both fixed and mobile WiMAX in collaboration with
other European operators within Eurescom (The European Institute for collaborative
research and strategic studies) and has been deploying fixed WiMAX in summer cottage
areas in an experimental purpose. Recently Síminn started deployment of an UMTS
network with HSDPA included in Iceland.
The Icelandic market is in many ways interesting. It is small, but developed and there is
a high purchasing power. The consumers are open to new products and technologies. For
an example, Iceland has the highest ADSL penetration in the world and a year after
Síminn started its IPTV service 19 % of the Icelandic households were subscribing,
which is a world record [1]. Still the Icelandic market is difficult because of the
country’s small population and the relatively big size of the island. One of the main
purposes of a special law, Act8/2005 2 on Third Generation Mobile Telephony, is to
guarantee that the rural areas will not be left out when it comes to 3G. This act applies to
the allocation of frequency ranges 1900-1980 MHz, 2010-2025 MHz and 2110-2170
MHz [2] Two thirds of the Icelandic population lives in the Reykjavik area, which makes
it by far the best area from market perspective.
No frequency band has yet been assigned for TDD in Iceland but it is likely that the
Icelandic Post and Telecom Agency will follow other European countries and the CEPT 3
recommendations. Hence it is likely that the frequency band 2500-2690 MHz will be
allocated partly for TDD and there will be a change for operators to deploy WiMAX
there.
1.2. Problem Definition
The objective of this thesis is to provide a techno-economic comparison of two wireless
broadband technologies, Mobile WiMAX and HSDPA. The comparison is divided into
two parts. The first part is a general overview and comparison of the two technology
standards. In the second part the deployment cost and operating cost over 10 years in
terms of CAPEX, OPEX and estimated revenues is estimated, for the case of a new
market entrant. The investigations will be performed for the city of Reykjavík.
1
1
Síminn is the largest telecommunication operator in Iceland. Its range of services includes fixed and
mobile subscriptions, Broadband/DSL, Live TV and Centrex network solutions. Síminn has about 80%
market share in fixed line telephony, 65% in the mobile telephony and 56% market share as an ISP.
Síminn operates a GSM network reaching 98% of the population and since September 2007 an UMTS
network that covers Reykjavik, Keflavik and Akureyri. [1]
2
The law states how frequencies should be assigned and what conditions the operators have to fulfill to
get the frequency license. The country is divided into four areas and the service has to reach 60% of
each of them. The law also states how fast the operator has to obtain this coverage. A better coverage
gives discount. The duration of the right to use the frequencies is 15 years per each block.
3
The European Conference of Postal and Telecommunications Administrations.
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1.3. Approach
Methodology
This thesis is partly based on studies on Mobile WiMAX carried out by Síminn in
collaboration with a few other European incumbent operators within Eurescom.
The Eurescom project aimed to clarify the role and usefulness of mobile WiMAX by
performing a set of business case analysis. To perform the analysis first radio planning
assumptions and link budget calculations were done, as this affects the network
dimensioning, which in turn determines the infrastructure cost. [3], [4]
In this thesis we will use the similar methodology but only one business case will be
considered, the one for a new entrant and the analysis will be performed for two
technologies, Mobile WiMAX and HSDPA.
In the first part of the thesis the subject will be introduced by giving an overview of the
two wireless broadband standards, this is covered in chapter 2. In this overview the
technical characteristics of both standards will be studied and a comparison between them
given. Other aspects like market position and future development will be briefly
discussed.
The second part, the techno-economic analysis, is covered in chapters 3, 4 and 5.
In chapter 3, a framework for the comparison is established by introducing system
models and establishing radio-planning assumptions. Then these assumptions are used to
do the network dimensioning that will give us two important parameters for the technoeconomic analysis, the cell radius and average throughput per channel.
In chapter 4 a framework for the business analysis is established and in chapter 5 the
results are presented and further analyzed in a sensitivity analysis. In chapter 6 the
conclusions are presented and discussed.
Tool
The OPEX and CAPEX calculations will be carried out by adapting a spreadsheet-based
model created by Telenor and used in the Eurescom project that this study is partly based
on. The tool was created to calculate the economical feasibility of a Mobile WiMAX
Business Case. This tool has been chosen for several reasons. First of all it fits the
purpose of this thesis well as it provides the output parameters we are looking for and
takes into account all aspects that we are interested in. It is also simple to alter to fit our
needs.
WiMAX
2.1.1 Background
WiMAX stands for Worldwide Interoperability for Microwave Access and is a wireless
broadband communication system defined in the IEEE 802.16 industry standards. The
WiMAX Forum is an organization formed to promote conformance and interoperability
of the IEEE 802.16 standards.
The IEEE 802.16-2004 (802.16.d) standard, also known as the fixed WiMAX standard,
was approved by IEEE in June 2004. It provides fixed, point-to-multi point broadband
wireless access service and is primarily used as a wireless metropolitan area network
(WMAN).
In 2005 IEEE approved the mobile WiMAX amendment, IEEE 802.16e-2005 (802.16.e).
In the 802.16e-2005 amendment the most important addition to the previous standards is
mobility with specifications of mobility management, extensible authentication protocol
(EAP) and handover.
Mobile WiMAX is based upon Orthogonal Frequency Division Multiple Access
(OFDMA).
Some of the features of Mobile WiMAX are:
• High Data Rates: Can theoretically support peak download data rates up to 63
Mb/s per sector and peak upload data rates up to 28 Mb/s per sector in a 10 MHz
channel, when MIMO 2*2 is used and DL:UL ratio is 1:0 and 0:1 respectively.
• Quality of Service (QoS): QoS measures for WiMAX include service
availability, data throughput, delay, jitter, and error rate.
• Scalability: Mobile WiMAX has been designed to be able to work in different
channel bandwidths from 1.25 to 20 MHz.
• Mobility: Optimized handover schemes with latencies less than 50 milliseconds
and flexible key management schemes are supported. Mobile WiMAX has been
tested for speeds up to 120 km/h.
[5]
These features make the technology suitable for a range of applications. Among the
applications that have been suggested for mobile WiMAX is to provide high speed data
services and other Internet services like VoIP for fixed, nomadic and mobile terminals, to
provide a wireless alternative to cable or DSL for last mile broadband access and to
connect hotspots with each other and the rest of the Internet. The only application we
will consider is the high speed Internet service to fixed, nomadic and mobile users.
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2.1.2 Technology
The IEEE 802 standards are a family of standards dealing with local area networks
(LANs) and metropolitan area networks (MANs). The standards mainly focus on the
lowest 2 layers of the Reference Model for Open Systems Interconnection (OSI)[6], the
Data Link layer and the Physical (PHY) layer. Furthermore, IEEE 802 splits the Data
Link Layer into two sub-layers, the Logical Link Control (LLC) sub layer and the Media
Access Control (MAC) sub layer. In broadband wireless networks, most of the things
happen in the MAC layer and the PHY (Air Interface) layer.
Figure 1. The layers of the OSI model, and the Data Link sublayers, LLC and
MAC.
The Physical layer
At the first level of the seven level OSI model there is the Physical layer, the most basic
network layer. Its main functions are providing an interface to physical transmission
media, modulation, coding, bit synchronization, flow control and circuit mode
multiplexing. [7]
Mobile WiMAX (802.16e-2005) uses a physical layer mode called scalable Orthogonal
Frequency Division Multiple Access (sOFDMA PHY) mode.
OFDM
Orthogonal Frequency Division Multiplexing is a multiplexing technique that divides the
input data stream into a large number of parallel substreams of reduced data rate and each
substream is modulated and transmitted on a separate orthogonal subcarrier. Each
subcarrier is modulated with a conventional modulation scheme. The reduced data rate
causes the symbol duration to increase and hence improves the robustness of OFDM to
delay spread. Because of the subcarriers orthogonality there will be no cross talk between
them, even though their spectra is very close or overlapping. By allowing the subcarriers
to overlap, the spectrum required is reduced and the bandwidth efficiency is increased.
OFDM signals are generated with efficient Inverse Fast Fourier Transform (IFFT), which
enables a large number of subcarriers (up to 2048) with low complexity. In the time
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domain the resources of an OFDM system are available by means of OFDM symbols and
in the frequency domain by means of subcarriers. For allocation to individual users the
time and frequency resources can be organized into subchannels. [5]
OFDMA
Orthogonal Frequency Division Multiple Access is a multiple-access/multiplexing
scheme that divides the channel in such a way that many users can share it. An
individual subcarrier or a group of subcarriers are assigned to different users and thus the
users can all use the same channel simultaneously.[8]
In other words OFDMA is a multi-user version of OFDM where subsets of subcarriers
can be assigned to different users. Different number of subcarriers can be assigned to
different users according to channel conditions and the type of service the user is
requesting. This is comparable to CDMA and how spreading codes can be used to assign
different users with different data rates.
Scalable OFDMA (S-OFDMA) is the modulation/multiple-access method used in
Mobile WiMAX to address the problem of different channel sizes in different countries.
With the scalability IEEE 802.16-2005 can support channel sizes ranging from 1.25 MHz
to 20 MHz. This is done by adjusting the FFT size based on channel size or bandwidth
while keeping the subcarrier frequency spacing fixed at 10.94 kHz.
Since the resource unit subcarrier bandwidth and symbol duration is fixed, the impact to
higher layers is minimal when scaling the bandwidth. [5]
To do the sub-channelization there are two types of subcarrier permutations:
1. Diversity permutation that draws subcarriers pseudo-randomly to form a
subchannel. This provides frequency diversity and inter-cell interference
averaging.
2. Contiguous permutations, which groups a block of contiguous subcarriers to form
a subchannel.
The diversity permutations include DL FUSC (Fully Used SubCarrier), DL PUSC
(Partially Used SubCarrier) and UL PUSC. The contiguous permutations include DL
AMC (Adaptive Modulation and coding) and UL AMC. AMC permutation enables
multi-user diversity by choosing the sub-channel with the best frequency response.
Diversity permutation is best suited for mobile applications, while contiguous
permutation works best for fixed, portable and low-mobility situations.
Time Division Duplex (TDD) frame structure
The 802.16-2005 PHY does support TDD and Full and Half-Duplex FDD operation but
TDD is the preferred duplexing mode and FDD will only be considered to address
specific market opportunities.
When using TDD only one channel is required for both downlink and uplink as opposed
to the two separate frequency channels of FDD. The advantages of TDD are that it
enables adjustment of the downlink/uplink ratio to efficiently support asymmetric
downlink/uplink traffic instead of fixed and equal DL and UL bandwidths. The ratio
between the uplink and downlink determines how time is split between them, for example
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the ratio 2:1 means that the UL gets two times more time for transmission than the
uplink. TDD also supports channel reciprocity, which is important when using MIMO
and other closed loop advanced antenna technologies. Transceiver designs are also
simpler for TDD implementations than FDD. On the other hand the discontinuous
transmission and reception of TDD reduces the average power of the system. [5], [9]
Modulation and Coding
In Mobile WiMAX support for QPSK, 16 QAM and 64 QAM is mandatory in the DL but
in the UL 64 QAM is optional. Both Convolutional Code and Convolutional Turbo
Code are supported.
The coding and modulation schemes supported in Mobile WiMAX can be seen in table 1.
To show how it is possible to vary the data rates by choosing different MCS levels, the
different PHY DL data rates for different MCS levels are also shown in Table 1 (for
PUSC mode and 10 MHz channel).
Modulation Code rate DL PHY data rate (10 MHz)
QPSK 1/2 (CTC) 6,34 Mb/s
QPSK 3/4 (CTC) 9,50 Mb/s
16 QAM 1/2 (CTC) 12,67 Mb/s
16 QAM 3/4 (CTC) 19,01 Mb/s
64 QAM 1/2 (CTC) 19,01 Mb/s
64 QAM 2/3 (CTC) 25,34 Mb/s
64 QAM 3/4 (CTC) 28, 51 Mb/s
64 QAM 5/6 (CTC) 31,68 Mb/s
Table 1. MCS levels and DL PHY data rates in Mobile WiMAX [5]
Other features of the PHY layer
The term Adaptive Modulation and Coding (AMC) is used to denote the matching of
the modulation, coding and other signal and protocol parameters to the conditions on the
radio link.
Hybrid Auto Repeat Request (HARQ) is a feature that enables fast response to packet
errors and asynchronous operation, with a variable delay between retransmissions.
Fast Channel Feedback (CQICH): A Channel Quality Indicator (CQI) channel is used
to provide channel-state information from the user terminals to the base station scheduler.
Relevant channel-state information that is fed back by the CQI channel includes: Physical
CINR, effective CINR, MIMO mode selection and frequency selective subchannel
selection.
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All combined HARQ, CQICH and AMC provide robust link adaptation in mobile
environments.
The MAC (Media Access Control) Layer:
At the second level of the OSI model there is the Data Link layer that can be divided into
two sub-layers, MAC and LCC. The MAC sub-layer serves as an interface between the
physical layer and the LCC sub-layer. It provides channel access control mechanisms
and addressing mechanisms (MAC address) that make communication between terminals
and/or networks possible. Also it provides the protocol and control mechanisms that are
required for several stations to share the same physical medium.
The MAC layer of the IEEE 802.16-2005 is quite complex and advanced. The main
features are the following:
Quality of Service (QoS):
Is a term that refers to control mechanisms that can provide different priority to different
users or data flows, or guarantee a certain level of performance in accordance with
requests from the application program.
For certain types of network traffic a defined QoS is required. For example:
• Voice over IP (VOIP): Requires maximum latency tolerance, jitter tolerance and
maximum sustained rate.
• Streaming multimedia: Minimum reserved rate, maximum sustained rate, latency
tolerance and traffic priority.
• File Transfer Protocol (FTP): Maximum sustained rate, minimum reserved rate
and traffic priority.
• Data transfer, web browsing: Maximum sustained rate, traffic priority.
In the Mobile WiMAX MAC layer, QoS is provided via service flows. First the base
station (BS) and the user-terminal establish a unidirectional logical link between the peer
MACs. The QoS parameters associated with the specific kind of data to be transmitted
define the transmission ordering and scheduling on the air interface. For whatever
service is in use the parameters can be dynamically managed through Media Access
Control (MAC) messages. This QoS mechanism applies to both DL and UL for a better
QoS in both directions. [5]
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MAC Scheduling Service
Is a scheduling service that is designed to deliver broadband data services in an efficient
way over time-varying broadband wireless channel. These data services include voice,
data and video. To achieve this the scheduling service uses the following properties:
•
•
•
•
•
Fast Data Scheduler: To efficiently allocate available resources in response to
bursty data traffic and time-varying channel conditions. Located at each BS for
faster response. In order for the scheduler to correctly determine the packet
transmission ordering, the data packets are associated to service flows with
defined QoS parameters. Because of the CQICH channel feedback the scheduler
can choose the best coding and modulation for each allocation.
Scheduling for both DL and UL
Dynamic resource allocation: Frequency-time resource allocation on a perframe basis is supported in both DL and UL. As the resource allocation is
delivered in Media Access Protocol (MAP) messages in the beginning of each
frame it can be changed on a frame-by-frame basis in response to traffic and
channel conditions. The amount of resource can range from one slot to entire
frame.
QoS Oriented: Data transport is handled on a connection-by-connection basis.
For each connection there is a single data service with a set of QoS parameters
that define its behavior.
Frequency Selective Scheduling: Provides different services for different types
of subchannels. For PUSC subchannels, where the subcarriers are pseudorandomly distributed across the bandwidth, the subchannels are of similar quality;
QoS with fine granularity and flexible time-frequency resource scheduling is
supported. For AMC subchannels, where the subchannels may have different
attenuation, mobile users can be allocated to their strongest subchannels.
Power Management
To enable power-efficient MS operation Mobile WiMAX supports Sleep Mode and Idle
Mode. In Sleep Mode the MS conducts pre-negotiated periods of absence from the
Serving Base Station air interface to minimize power usage and usage of the Serving
Base Station air interface resources. In Idle Mode the MS is periodically available for
DL broadcast traffic messaging without registration at a specific BS.
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Handoff
The IEEE 802.16e-2005 standard supports three types of handoff:
Hard Handoff (HHO): Is the mandatory mode and has been improved with the
goal of keeping Layer 2 delays to less than 50 milliseconds.
Fast Base Station Switching (FBSS): Is an optional mode. The set of BS that
support FBSS is called an Active Set and one of the BS is defined as the Anchor BS.
When operating in this mode the MS only communicates with the Anchor BS. At every
time the MS chooses the BS with the strongest signal to be the Anchor BS.
Macro Diversity Hand-over (MDHO). Is an optional mode. The BS’s that
support MDHO are part of an Active Set maintained by the MS and BS. One of the BS’s
in the Active Set is defined as the Anchor BS. As opposed to FBSS in MDHO the Ms
communicates with all BSs in the Active set, but the regular mode of operation is the
particular case when there is only one BS in the Active Set. In the DL diversity
combining is performed at the MS as two or more BSs provide synchronized
transmission of MS downlink data. In the UL selection diversity is performed as the
transmission from a MS is received by multiple BSs.
Network Architecture
The end-to-end network architecture is not part of the IEEE 802.16e-2005 standard. As
IEEE usually only defines the PHY and MAC layers. However operators and vendors
have formed working groups to define standard network reference models. In Figure 2 a
basic view of the all-IP Mobile WiMAX network can be seen.
Figure 2. Network Architecture of Mobile WiMAX
The three basic domains are:
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User Terminals : Mobile, portable and fixed devices with WiMAX support. This could
be for example cellular phones, MIDs (Mobile Internet Devices), UMPCs (Ultra Mobile
PCs), laptops or Desktops.
Access Service Network (ASN) : Provides a way to connect user terminals using
OFDMA air interface to an IP backbone with session continuity (a session is not drop
when user moves between wireless environment). An ASN consists of BSs and Access
Gateways. The set of network functions in ASN include:
Network discovery and selection of the preferred CSN/NSP (Network Service Provider)
Network entry with IEEE 802.16e-2005 based layer 2 connectivity and AAA proxy.
Relay function for IP Connectivity.
Radio Resource Management.
Multicast and Broadcast Control.
Foreign agent functionality for inter-ASN mobility
Paging and Location Management.
Data forwarding.
Service flow authorization.
Quality of Service.
Admission Control and Policing.
Connectivity Service Network (CSN) : is defined as a set of network functions that
provide IP connectivity services to the mobile subscribers. A CSN consists of network
elements such as routers, AAA(Authentication, Authorization, Accounting)
proxy/servers, user databases and Interworking gateway devices. A CSN is deployed by a
NSP. AAA or Home Agent residing in CSN allocates the IP address. AAA also performs
authentication, authorization, and accounting. Communication is through a RADIUS
protocol. The policy server residing in the CSN is responsible to store the policy and QoS
info of each subscriber, which is communicated to ASN during service flow creation.
CSN is also responsible to access other IP networks.
2.1.3.Other features of Mobile WiMAX
Smart Antenna Technologies
Using OFDMA makes it possible for Mobile WiMAX to use smart antenna operations in
rather simple way as they can be performed on vector-flat subcarriers and no complex
equalizer are required to compensate for frequency selective fading. The MIMO
technologies can be divided into the following three categories:
• Spatial Multiplexing: To enhance the peak data transmission rate and overall
throughput by using multiple streams with multiple antennas.
• Space-Time Coding: A transmission diversity method for enhancing transmission
robustness.
• Beamforming: The received signal gain is improved and interference reduced
with better coverage, higher capacity and reduced outage probability.
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By using Adaptive MIMO Switching (AMS) between multiple MIMO modes, the MIMO
system can use the transmission techniques one at a time or all together as is best at each
time. In that way the spectral efficiency can be maximized with no reduction in coverage
area.
Fractional Frequency Reuse
To maximize spectral efficiency Mobile WiMAX support the frequency reuse of one. In
other words every cell/sector uses the same frequency. Normally, this can lead to heavy
cochannel interference (CCI) and reduction in connection quality, especially for users at
the cell edge. However, since in Mobile WiMAX each user operates on a subchannel
that only occupies a small fraction of the bandwidth, configuring subchannel usage can
significantly reduce the interference.
Multicast and Broadcast Service (MBS)
MBS is a technology that can be used to broadcast (or multicast) multimedia , similar to
DVB-H, MediaFLO and DMB. MBS uses a Single Frequency Network (SFN) to obtain
high data rate and coverage. It supports flexible allocation of radio resources, has low
MS power consumption and low channel switching time.
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2.
properties of their spreading codes.
24
Scrambling
In addition to spreading, part of the process in the transmitter is the scrambling operation.
This is needed to separate terminals or base stations from each other. Scrambling is used
on top of spreading by using scrambling codes. It makes the signals from different
sources separable but doesn’t affect the bandwidth or the symbol rate as the chip rate is
already achieved in spreading by the spreading codes.
Main features in W-CDMA systems (R’99)
In Table 2 some of the main features of W-CDMA systems are listed. Those features and
others are better explained below.
Multiple access method
DS-CDMA
Duplexing method
Frequency division duplex/(time division duplex)
Chip rate
3.84 Mcps
Frame length (TTI)
10 ms
Multirate concept
Variable spreading factor and multicode
Multiuser detection, smart
antennas
Supported by the standard, optional in the
implementation
Modulation
QPSK
Physical layer spreading factors
4 - 256
Table 2. Some features of W-CDMA
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Multiple Access Method: DS-CDMA
Multiple Access schemes are used to allow multiple users to access the radio resource in
a way that maximizes the use of resource and minimizes the interference between users.
In CDMA each user uses a different spreading waveform, which means that two or more
different users can use the same carrier frequency and still transmit simultaneously.
There doesn’t need to be any difference in time or frequency between the different users,
only different waveforms. (See explanation of W-CDMA above).
Frequency Division Duplexing (FDD)
The basic mode of duplex is frequency division duplex, that is one 5 MHz channel is
used for uplink and another 5 MHz channel is used for the downlink. TDD is also
supported but FDD is by far the most common mode in UMTS WCDMA systems.
Frequency duplex means that the radio transmitter and receiver operate at different
frequencies and can thus send and receive at the same time without interference.
FDD is more efficient than TDD in the case of symmetric traffic. In this case TDD tends
to waste bandwidth during switch over from transmit to receive, has greater inherent
latency, and may require more complex, more power-hungry circuitry. On the other hand
TDD allows for assymetric traffic and has some other advantages (see TDD in WiMAX
chapter).
Chip rate
Chip rate is the number of bits per second used in the spreading signal. A different
spreading signal is added to the data signal to code each transmission uniquely. The
number of chips (bits) in the spreading signal is significantly greater than the data bits.
Chip rate is measured in "megachips per second" (Mcps), which is millions of chips per
second. In WCDMA the chip rate is 3.84 Mcps, which leads to a carrier bandwidth of
about 5 MHz.
Frame length
Frame length is also known as Transmission Time Interval (TTI). Before data is
transmitted it is divided into blocks and then the bits in the block are encoded and
interleaved (arranged in a non-contiguous way). This is done to make the data less
sensitive to fading and interference on the radio link. The length of time required to
transmit one such block determines the TTI.
When the data is then received at the other end it is de-interleaved and decoded. But first
all the bits of the specific block must be received. When all the bits of the block have
been decoded and de-interleaved the receiver can estimate the bit error rate (BER). So as
the shortest decodable transmission is one TTI the shortest period over which BER can be
estimated is also one TTI.
In networks with link adaptation (e.g. HSDPA and Mobile WiMAX) information about
the estimated BER are used to adapt to the condition on the link. The shortest possible
interval between reports of the BER are one TTI. So a very short TTI helps the network
to adapt quickly to changing conditions in the radio link. On the other hand a longer TTI
increases the efficiency of error-correction and compression techniques and the effect of
26
interleaving. In WCDMA (R’99) the shortest TTI is 10 milliseconds but 20ms, 40ms
and 80ms are also supported.
Variable user data rates
W-CDMA supports highly variable user data rates, that is bandwidth can be obtained on
demand. The user data rate is kept constant during each 10 ms frame. However, the data
capacity among the users can change from frame to frame. This fast radio capacity
allocation will typically be controlled by the network to achieve optimum throughput for
packet data services.
One of the things used to support variable user rates is the Orthogonal Variable Spreading
Factor (OVSF). Different spreading factor means different code length. Different
messages with different spreading factors (different code length) are combined and the
orthogonality between them is kept. As the chip rate remains the same for all codes the
short ones will be transmitted at a higher information rate than longer ones.
Another thing used to support variable user rates is multicode transmission. Then each
user can have data sent over more than one channel (that is each user gets to use more
than one spreading or channelization codes).
Channelization Codes
Codes used to separate the different channels that may be present on a certain frequency
in a CDMA system.
To support a variety of data rates and spreading factors, it is necessary to chose
channelization codes that are orthogonal no matter what their length are. WCDMA uses
Orthogonal Variable Spreading Factor (OVSF) codes. Depending on the number of
physical channels used and their data rate, the number of available channelization codes
varies.
The number of voice channels per carrier can be approximated to 250. (256 available
orthogonal codes, minus some control channels).
Softer and Soft handover
During softer handover, a mobile station is in the overlapping cell coverage area of two
adjacent sectors of a base station. The communications between MS and BS take place
concurrently via two air interface channels, one for each sector separately. This requires
the use of two separate codes in the downlink direction, so that the MS can distinguish
the signals. The two signals are received by means of Rake processing; the fingers need
to generate the respective code for each sector for the appropriate despreading operation.
During soft handover, a mobile station is in the overlapping cell coverage area of two
sectors belonging to different BSs. As in softer handover, the communications between
MS and BS take place concurrently via two air interface channels from each BS
separately. Both channels are received at the MS by maximal ratio combining Rake
processing.
27
2.2.3 New features in HSDPA (release 5)
HSDPA was designed to increase downlink packet data throughput of UMTS by means
of fast physical layer (L1) retransmission and transmission combining as well as fast link
adaptation and fast scheduling controlled by the BS.
Several new channels are introduced in release 5. A new transport channel named HighSpeed Downlink Shared Channel (HS-DSCH) is the primary radio bearer. For the
associated signaling a channel called high-speed shared control channel (HS-SCCH) has
been added in the downlink and in the uplink the high-speed dedicated physical control
channel (HS-DPCCH) that carries information about the link condition.
High-Speed Downlink Shared Channel (HS-DSCH)
HS-DSCH is the channel used to send packets on the downlink to the UEs and comes
instead of the downlink shared channel (DSCH) used in R’99.
Similar to the DSCH, the HS-DSCH resources can be shared between all users in a
sector. The primary channel multiplexing occurs in the time domain, with a TTI of 2ms
(or three slots.) In R’99 the shortest TTI is 10ms. This significant reduction of the TTI
size will improve the link adaptation rate and the AMC efficiency as well as reducing the
round trip delay between the BS and the UE.
In DCH (R’99) it was possible to use variable spreading factor between 4 and 512, in
HSDPA a fixed Spreading Factor of 16 is used for code multiplexing. Therefore, within
each 2 ms TTI a maximum of 15 parallel codes allocated to the HS-DSCH can be used
for code multiplexing. All 15 codes can be assigned to one user or split between several
users in the sector, during each TTI. The number of parallel codes allocated to each user
depends on cell loading, QoS requirements and the UE code capabilities (5, 10 or 15
codes). [11]
The following list is a list of the main differences between HS-DSCH and DCH (R’99).
Better explanations follow below.
•
•
•
•
•
•
•
Use of physical layer retransmission and retransmission combining (H-ARQ)
Lack of fast power control, link adaptation and AMC used instead.
Support of higher order modulation (16 QAM)
Shorter TTI (2ms)
Lack of soft handover
Fixed spreading factor
BS based Fast packet scheduling for controlling allocation of users.
28
Hybrid Automatic Repeat Request (H-ARQ): Automatic Repeat reQuest is an error
control method for data transmission. If a receiving part of the system has received a
correct data frame it sends an ACK (acknowledge character) message to the transmitting
part of the system. If it receives an erroneous data frame it sends an NACK (negative
acknowledge character) and the packet is discarded. In H-ARQ two methods are used to
improve this scheme: Chase combining and incremental redundancy (IR). In chase
combining the erroneous packet is not discarded but stored and later combined with the
retransmitted packet to increase the probability of successful decoding. In IR the
different transmissions are coded differently instead of the same code being repeated as
in chase combining. [12]
Adaptive Modulation and Coding (AMC): Denotes the matching of the modulation,
coding and other parameters to the condition on the radio link. In HSDPA AMC is used
to ensure that all users achieve the highest possible data rate regardless of its location in
the cell. The modulation scheme and coding is changed for each user depending on signal
quality and cell usage that has been reported as feedback from the UE. QPSK is the
initial modulation scheme but in good ratio conditions 16QAM can be used to improve
the data throughput significantly. The spreading factor cannot change but the coding rate
can change between 1/4 and 3/4. The higher coding rate reduces the number of errors.
[13] & [14]
Fast Packet Scheduling: Allows the HS-DSCH channel to take advantage of favorable
channel conditions to make best use of available radio conditions. Each EU periodically
reports on the signal quality to Node B (Base Stations). That information is then used to
decide which users will be sent data on the next 2ms frame and how much data can be
sent to each user.
Both Convolutional Coding and Turbo coding are supported but previously only CC has
been supported.
2ms TTI: The shorter time interval enables higher speed transmission in the physical
layer, so that the system will be more reactive to changing link conditions and can
reallocate capacity to users quicker.
Handover: HSDPA does not use soft handover. This is because the AMC, H-ARQ and
fast packet scheduling are techniques that require a constant one-to-one connection
between the HSDPA mobile terminal and the BS. Thus hard handover, in which the
destination BS is selected each time the cell changes, is needed. Since the only traffic
supported by HSDPA is delay-tolerant data traffic soft handover is also not as necessary
as when dealing with voice traffic.
29
A higher modulation scheme, 16QAM, has also been added to the already existing QPSK
modulation used for the R’99 channels. With also a lower encoding redundancy this
gives an increased instantaneous peak data rate.
The modulation to be used at each time is adapted to the link conditions. The code rate is
also adapted to the condition. HS-DSCH uses Turbo coding and supports the following
code rates: 1/4, 1/2, 5/8 and 3/4. In addition to the modulation scheme and code rate HSDSCH can also choose different number of multi-codes to provide different data rates to
different users. Table 3 shows the UE categories defined in release 5.
Category Max nr. of
parallel codes
per HS-DSCH
Minimum interTTI interval
Transport
channel bits per
TTI
Achievable
m aximum data
rate (Mb/s)
1,2 5 3 7298 1,2
3,4 5 2 7298 1,8
5,6 5 1 7298 3,6
7,8 10 1 14411 7,2
9 15 1 20251 10,2
10 15 1 27952 14,4
11 5 2 3630 0,9
12 5 1 3630 1,8
Table 3. HSDPA terminal capability categories [15]
Changing the coding rate and the modulation scheme can largely vary the terminal data
rate. Table 4 shows the maximum data rates when the number of codes is kept constant at
15 codes but the coding rate and the modulation scheme are varied.
Modulation Effective code rate Max throughput (Mb/s)
QPSK 1/4 (turbo) 1,8
QPSK 1/2 (turbo) 3,6
QPSK 3/4 (turbo) 5,3
16 QAM 1/2 (turbo) 7,2
16 QAM 3/4 (turbo) 10,2
16 QAM 4/4 (turbo) 14,4
Table 4. Peak data rates with number of codes fixed at 15 [15],[10]
Other channels
In addition to the HS-DSCH channel, three other physical channels are new in HSDPA.
30
High Speed-Shared Control Channel (HS-SCCH):
Informs the user that data will be sent on the HS-DSCH 2 slots ahead. HS-SCCH has a
fixed rate of 60 kbps (spreading factor 128), which allow 40 bits per slot to be carried.
Part of the information carried on HS-SCCH like which codes to de-spread in the HSDSCH, needs to be available before beginning to use the HS-DSCH. Thus the HS-SCCH
is divided into two parts.
The first part contains the most urgent information about the modulation and coding.
This allows terminals to support only 5 or 10 codes even though the code space allocation
is 15 codes.
The second part carries information that is not as urgent. Which ARQ process is being
transmitted and if the transmission is new or related to an older transmission.
When HSDPA is operated using the time multiplexing principle there can only be one
HS-SCCH channel configured. This means that only one user can receive data at a time.
When code multiplexing is being used, more than one HS-SCCH channels are needed. A
single terminal cannot use more than 4 HS-SCCH channels.
The channel coding is one-third convolutional coding.
Uplink High Speed-Dedicated Physical Control Channel (HS-DPCCH):
Carries acknowledgement information and current channel quality indicator (CQI) of the
user from the terminal to the base station. The base station then uses this value to enable
the link adaptation and physical layer retransmissions. The H-ARQ feedback informs the
base station whether the packet was decoded correctly or not and the CQI informs the
base station scheduler about what data rates the terminal expects to be able to receive at
that moment.
The HS-DPCCH has a fixed spreading factor of 256 and a 2ms (three slots) structure.
The fist slot is used for the H-ARQ information and the remaining to for the CQI
information. An associated Dedicated Physical Channel (DPCH), a parallel code
channel, provides the signaling.
31
High Speed-Physical Dedicated Shared Channel (HS-PDSCH):
Is mapped to the HS-DSCH transport channel that carries actual user data.
The table below shows some of the differences between WCDMA (R’99) and HSDPA
(R’5):
WCDMA (R’99) HSDPA (R´5)
Modulation Scheme
QPSK QPSK/16QAM
Multiplexing Scheme
(Downlink)
DS-CDM DS-CDM/ TDM
Duplex Method
FDD FDD
Channel Bandwidth
5 MHz 5 MHz
Frame Size
10 ms (20, 40 and 80 ms) 2 ms
Coding
Cc Cc, Turbo
DL Peak Data Rate
384kbps-2Mb/s 14 Mb/s
Frequency Reuse Factor
1 1
Table 5. Differences between WCDMA (R´99) and HSDPA
32
End to End Network Architecture
The UMTS architecture: An UMTS network can be divided into three interacting
domains:
•
•
•
Core Network (CN):Provides switching, routing and transit for user traffic
and contains the databases and networking management functions.
UMTS Terrestrial Radio Access Network (UTRAN): Provides the air
interface access method for UE.
User Equipment (UE): The handset that the user needs to connect to the
system. This can be for example a cellular phone or a laptop.
Figure 3. UMTS network architecture
A mobile radio network generally includes a set of base stations and base station
controllers. In UMTS this network is called the UMTS terrestrial radio access network
(UTRAN), a base station is called a Node B and a base station controller is called a radio
network controller (RNC).
The UTRAN communicates with mobile stations (UEs) via a Uu interface and with a
core network (CN) via an Iu interface. The RNCs are connected to each other via a lur
interface and to the BS (Node B) via a lub interface.
33
2.3 Comparison of WiMAX and HSDPA
2.3.1 Technical comparison
The most fundamental difference between the two technologies is based on that HSDPA
evolved from 3G CDMA standards and networks that provide mobile voice services
while WiMAX has evolved from system concepts designed for fixed wireless access.
WiMAX is optimized for broadband data services where as mobility was an additional
feature added to the standard.
Similarities :
Despite their different background there are several technical features that the two
technologies have in common. Those include:
• Adaptive Modulation and Coding (AMC)
• Hybrid ARQ
• Fast Scheduling
• Hard Handoff
All those things have already been mentioned in the overview chapters. Both standards
support AMC. Both technologies have similar approach on HARQ and support the chase
combining (cc) method. The advantage of using HARQ CC is that since the
retransmissions are identical, it is easy to extend to different transmission techniques such
as MIMO.
In order to enable fast response to traffic and channel condition variations both standards
have included Fast Scheduling.
However there is a little difference in that WiMAX applies the fast scheduling on a per
frame basis and broadcasts the downlink/uplink scheduling in the MAP messages at the
beginning of each frame. While HSDPA supports dedicated scheduling, where only a
subset of UEs with pending data is selected to transmit over a given time interval with
selected rates restricted. The user devices periodically transmit an indication of the
downlink signal quality and the base station uses that information to decide which users
will be sent data on the next 2 ms frame and how much data should be sent to each user.
The network bandwidth allocated to HSDPA users is determined by the network and is
“semi-static”. It can be modified while the network is operating but not on a per frame
basis.
Neither WiMAX nor HSDPA supports the traditional mobile network soft handover.
Instead HSDPA uses “Network initiated Hard Handover” and WiMAX “Network
Optimized Hard Handover”. Both methods are more bandwidth efficient than the soft
handover where more than one BS in a mobile active set of base stations send
simultaneously in order to minimize the handover delay. [16,page 27-30]
34
Differences
HSDPA is based on a traditional mobile telephony while Mobile WiMAX is based on
fixed wireless broadband technology. The Mobile WiMAX physical layer is based on an
OFDMA while HSDPA is a CDMA based system. OFDMA has some advantages over
CDMA and it is likely that future systems will be based on OFDMA technology. For
exampleLTE, the next generation of UMTS systems, will be based on OFDM. [17], [15]
Some of the features of OFDMA that make it well suited for high speed wireless
networks are listed below:
Tolerance to Multipath and Self-Interference : Since the subchannels maintain their
orthogonality in a multipath channel the number of multipath components does not limit
the performance of the system as long as the multipath is within the cyclic prefix
window.
Scalable Channel Bandwidth :
Orthogonal Uplink Multiple Access: In OFDMA systems users are allocated different
portions of the channel where as in CDMA each user transmits over the entire channel.
This means that in OFDMA there is no multiple access interference (MAI) between
multiple users. In CDMA orthogonal spreading codes are used to avoid MAI but due to
the uplink synchronization issues, asynchronous CDMA is used in the uplink in most
practical CDMA systems and there will be interference and reduced spectral efficiency.
Frequency Selective Scheduling: As only a portion of the channel is occupied by the
WiMAX signals frequency selective scheduling can be used to choose sub channels with
the best condition at each time and hence improve QoS.
Advanced Antenna Technology: For smart antenna technologies the processing
complexity scales with the channel bandwidth. Since in CDMA the signals occupy the
entire bandwidth this becomes quite a problem when used in broadband wireless channels
and limits the options of using advanced Antenna Technology. OFDMA on the other
hand is well suited for these technologies.
From the beginning IEEE 802.16 was designed as an all-IP technology. It is based on an
advanced all-IP core network, which includes interworking with IP Multimedia
Subsystems (IMS) and with 2G, 3G and IP-based technologies.
HSDPA supports GERAN (GSM EDGE Radio Access Network) and UTRAN (UMTS
Terrestrial Radio Access Network) based access networks. GERAN and UTRAN can
carry many traffic types from real-time Circuit Switched to IP based Packet Switched.
This in turn means a high degree of compexity compared to an all-IP architecture. In the
3GPP LTE (Long Term Evolution) an All-IP Network is proposed as the future of
UMTS.
35
Other differences
Duplex method : Mobile WiMAX will most commonly use TDD while HSDPA
generally uses FDD. FDD is more efficient than TDD in the case of symmetric traffic but
TDD allow for assymetric traffic and as the downlink traffic is usually much heavier than
the uplink traffic, assymetric traffic can be very practical. TDD requires system-wide
frame synchronization to counter interference issues and the discontinous transmissions
reduce the average power. On the other hand TDD assures channel reciprocity and thus
better supports link adaptation, MIMO and other advanced antenna technologies.
Modulation : Mobile WiMAX supports QPSK, 16 QAM and 64 QAM modulation but
HSDPA only supports QPSK and 16 QAM (although in release 7 64 QAM has been
added). In other words Mobile WiMAX supports higer order modulation than HSDPA.
With 16 QAM 4 bits can be carried per symbol instead of 2 bits per symbol with QPSK.
With 64 QAM 6 bits can be carried per symbol and thus higher data rates can be reached.
Table 6, gives an overview of some of the features of Mobile WiMAX and HSDPA.
HSDPA Mobile WiMAX
Base Standard
WCDMA IEEE 802.16e-2005
Duplex Method
FDD TDD
Downlink
CDM-TDM OFDMA
Uplink Multiple Access
CDMA OFDMA
Channel Bandwidth
5 MHz Scalable: 5,7,8.75, 10 MHz
Frame size
DL=2 ms UL=2/10ms 5 ms TDD
Modulation DL
QPSK, 16QAM QPSK, 16QAM, 64QAM
Modulation UL
BPSK, QPSK QPSK, 16QAM
Coding
CC, Turbo CC, Turbo
DL Peak Data Rate
14,4 Mb/s 46 Mb/s DL/UL =3:1
(BW=10MHz and 2*2 MIMO)
H-ARQ
Fast 6-channel Asynchronous
CC
Multi Channel Asynchronous
CC
Scheduling
Fast scheduling in DL Fast Scheduling in DL and UL
Handoff
Network initiated Hard
Handoff
Network optimized Hard
Handoff
Table 6. Comparison of some of the features of Mobile WiMAX and HSDPA
36
2.3.2 Market situation and opportunities
Many operators around the world have invested in R’99 UMTS networks. For them
HSDPA offers a significant service upgrade and an opportunity to accelerate the Return
of Investment. HSDPA networks are already widely deployed and handsets have been on
the market since 2006.[18]
For Mobile WiMAX it is necessary to build new networks, and the manufacturing of
handsets has been quite complicated and required a totally new set of chips and
platforms. The fact that Intel, a giant on the semiconductor and microprocessor market,
is a leader in promoting WiMAX and has included its WiFi/WiMAX solutions in it’s 5th
generation Centrino platform for labtops, Montevina, and its next generation platform for
MID’s and UMPC’s could help the promotion of WiMAX. [19]
Current and future deployment of mobile WiMAX
Deployment of mobile WiMAX is yet in early stages. However many companies have
plans of deployment and some are already on the market. In South Korea a technology
called WiBro has been developed by the Korean telecommunication industry. WiBro is a
wireless broadband Internet based on the IEEE 802.16-2005 standard and is interoperable
with WiMAX. In 2005 Samsung introduced the world’s first Wibro phone, M8000, and
Wibro PDA. The services offered in the M8000 include broadcasting, home networking,
video-conferencing and video on demand. [20] ,
In the US, Sprint Nextel announced in 2006 that they had chosen WiMAX as its next
generation 4G technology platform. Working with Intel, Motorola and Samsung, Sprint
Nextel are planning on a nationwide network and mobile WiMAX products that will
support advanced wireless broadband services for computing, portable multimedia,
interactive and other consumer electronic devices.[17] Motorola has been developing
Mobile WiMAX chipsets to use in its WiMAX devices in cooperation with Texas
Instruments and the first chipsets are scheduled to support commercial Motorola WiMAX
devices in 2008. [21],[22] Also Nokia is planning on introducing its first Mobile
WiMAX handset in 2008, based on a Intel/Nokia chips. [14] LG is another manufacturer
that is involved in WiBro/WiMAX.
Current and future deployment of HSDPA
In November 21, 2007 GSA, the Global mobile Suppliers Association, confirmed that
154 HSDPA networks had entered commercial service in 71 countries. [23]
Also according to the GSA, 403 HSDPA devices are announced. Those include 203
phones/consumer devices, 39 wireless routers, 61 laptops and 100 devices for laptop
connectivity (USB modems etc).
The number of HSDPA networks, devices and subscribers is constantly growing. For
example WCDMA/HSDPA was responsible for 75% of the mobile subscription growth
in Western Europe in Q3 2007. [23]
37
The next upgrade of the UMTS protocol (release 6) includes High Speed Uplink Packet
Access (HSUPA) that provides improved up-link performance of up to 5.76 Mb/s
theoretically. The standard is already established and a small number of networks have
already been launched. A new 3GPP technology, LTE will use scalable OFDM air
interface, MIMO, 64 QAM and have an all-IP network.
Performance studies
A few studies have been carried out to compare the performances of Mobile WiMAX and
HSDPA.
The WiMAX Forum published the study:Mobile WiMAX-Part II: A Comparative
Analysis in May 2006. [5] In this study Mobile WiMAX is compared to HSPA and
EVDO (Rev A & Rev B). The simulations results show a clear advantage of Mobile
WiMAX in both spectral efficiency and sector throughput. For Mobile WiMAX the net
information throughput per channel was found to be 14.1 Mb/s in the downlink using 10
MHz bandwidth, TDD 3:1 and MIMO and 9.1 Mb/susing SIMO. For HSDPA this
number was 3.9 Mb/s using 2 * 5 MHz FDD and single antenna Tx and dual antenna Rx
(1x2, SIMO) with RAKE receivers.
In the paper “The Performance Comparison between WiBro and HSDPA” a team of
Network Engineers at the Network R&D Center of SK Telecom in Korea published the
results of their performance comparison of WiBro and HSDPA. The two factors
compared where coverage and capacity. The team concluded that the overall
performance of WiBro was better than HSDPA. The biggest difference was that WiBro
showed better robustness in multi-path fading channels. On the other hand the shorter
TTI of HSDPA, 2ms for HSDPA and 5ms for WiBro, made HSDPA more robust to the
dynamic channel variation. Another advantage of HSDPA, according to the Korean
Team, is that it uses the well-established WCDMA network. [13]
In may 2007 Ericsson published the paper “ HSPA, the undisputed choice for mobile
broadband”. In the paper the performance of HSPA and Mobile WiMAX is said to be
comparable. “Both technologies offer similar peak data rates, spectral efficiency and
network complexity”. However, in this paper the coverage of HSPA is found to be better
than the coverage of Mobile WiMAX. [9]
38
3.1 Network dimensioning and planning
3.1.1 Frequency band
The frequency band in which a network is operated is an important factor of the network
dimensioning. The use of radio frequency bands is regulated by governments. When
regulators have decided how a certain frequency band should be used and regulated then
frequency licenses are allocated to operators that fulfill the conditions, for example
through auctions.
Radio communication technologies are designed to be deployed in certain frequency
bands. Cellular networks use the UHF band whose frequency is between 300 MHz and 3
GHz. The signal propagation characteristics are better in the lower frequency bands.
Many radio communication standards can be designed for use in the same frequency
band but only one can be deployed in a particular area in a certain frequency band.
That´s why the regulations and allocations are needed. Therefore many standards define
several different frequency bands that the networks can be operated in. For example 15
different FDD paired frequency bands and 6 different TDD frequency bands are defined
in the UMTS standard. [24]
Networks based on the IEEE 802.16e-2005 standard will operate on licensed bands
between 2 GHz and 6 GHz.
Release-1 Mobile WiMAX profiles cover 5, 7, 8.75, and 10 MHz channel bandwidths for
licensed spectrum allocations in the 2.3 GHz, 2.5 GHz, 3.3 GHz and 3.5 GHz frequency
bands. [5]
So in which frequency band a network will be operated can depend on the standard,
regulations in the selected geographical area and possibly the preferences of the operator.
In Iceland a special law, Act8/2005 on Third Generation Mobile Telephony states how
frequencies for UMTS networks should be assigned and what conditions the operators
have to fulfill to get the frequency license. This act applies to the allocation of frequency
ranges 1920-1980 MHz, 2010-2025 MHz and 2110-2170 MHz, that is band I according
to 3GPP specifications. [2]
No frequency band has yet been assigned for WiMAX in Iceland but it is likely that the
Icelandic Post and Telecom Agency will follow other European countries, in particular
the Nordic countries.
The European Conference of Postal and Telecommunications Administrations (CEPT)
has recommended that the frequency band 2500-2690 MHz should be allocated as 2 x 70
MHz for FDD and 50 MHz for TDD. Some regulators think that there is a bigger
demand for TDD than the CEPT guidelines imply. Norway has decided to allocate 2 x
40 MHz for FDD and 100 MHz for TDD.
The Swedish National Post and Telecom Agency has also announced that it will issue
licenses in the 2500-2690 MHz frequency band through an auction planned for the first
half of 2008. The licenses are service and technology neutral. That is, they can be used
for mobile telephony or wireless broadband services. [25],[26]
39
In order to make the design of our system as realistic as possible we have chosen to use
the 2.5 GHz band as the operating frequency band for mobile WiMAX and as the
frequency ranges 1920-1980 MHz, 2010-2025 MHz and 2110-2170 MHz have already
been allocated to UMTS in Iceland we have chosen the 2.0 GHz band as the frequency
band for HSDPA.
3.1.2 Fading model
In mobile systems the radio link conditions are constantly changing. Thus the signal
strength varies as a function of time and deviates around a mean value. To take the
uncertainty of the signal strength into account fading models are used.
When electromagnetic waves meet obstructions on their way through the air, the
wavefronts are scattered and the waves travel along multiple paths. The scattered portions
of the signal arrive at different times at the receiver and have been affected in different
ways. This problem is called fading and refers to time variations in the received signal
power because of changes in the path or the medium that the signal has traveled through.
Fading is divided into small-scale fading (also called multipath fading or fast fading) and
large-scale fading (also called shadowing or slow fading).
Small-scale fading happens because of small obstructions in the propagation path or
small movements of the mobile station. Large-scale fading happens because of large
movements or large obstructions in the propagation path.
To analyze the effects of fading, mathematical channel models are used. Fading channel
models are divided into categories depending on some properties. Small-scale fading
channels can be divided into categories based on the channels multipath time delay
spread (Tm ), Doppler spread (Bd ), coherence bandwidth (Bm ) or coherence time (Td ).
These parameters are related in the following way:
Bd = 1/ Td and B m =1/ T m
By looking at the coherence bandwidth/delay spread we can divide small-scale fading
channels into frequency selective fading and frequency nonselective fading channels.
The coherence bandwidth is the range of frequencies over which the channel can be
considered flat (i.e. the channel passes all spectral components with equal gain and linear
phase. [8]
Frequency selective fading : If the bandwidth of the input signal is larger than the
coherence bandwidth of the channel, the different frequency components of the signal
will be subject to different attenuation and phase shift. Hence the distortion is said to be
frequency selective and if the distortion leads to sharp drop in amplitude in some part of
the spectrum we have frequency selective fading. [8]
Frequency nonselective (flat) fading : Happens when the signal bandwidth is smaller
than the coherence bandwidth. An amplitude variation will be over the signals entire
frequency spectrum. Thus the shape of the waveform does not change, only the received
power level. [8])
40
In broadband wireless systems, the symbol rate is usually high. If the bandwidth of the
signal becomes greater than the coherence bandwidth we get frequency selective fading.
One way to avoid this problem is to use sub-channels. This is the method used in OFDM
and thus in the IEEE 802.16e standard. Then we get many narrowband flat fading subchannels instead of one broadband frequency selective fading channel.
Shadow fading distribution is usually modeled as a lognormal distribution that describes
the variation of the decibel value of the mean signal as a normal or Gaussian distribution.
Multipath fading is usually modeled using Ricean or Rayleigh distributions. The models
assume that the signal is sufficiently narrowband so that the fading is flat, i.e. not
frequency-selective.
OFDMA and CDMA systems both have quite effective but different methods to combat
multipath fading.
In OFDM systems, a wide frequency band is divided into multiple subcarriers, each of
which is assumed to experience flat fading.
In CDMA rake receivers are used that have several fingers that differ a little in time to
tune into the different components of the multipath signal. Then each component is
decoded independently and then they are combined to make use of path diversity.
In UMTS R’99 the fast fade margin is defined as the headroom needed in the MS TX
power to maintain adequate closed loop fast power control. HSDPA does not use closed
loop fast power control and thus does not need this headroom.
As both systems are capable of significantly reducing the multipath fading and even
taking advantage of it, there is no need for a big fast fading margin.
In the link budget only one fading margin is given that is supposed to include both fast
and slow fading (a UE can not move both fast and slow at the same time but there can
always be obstacle of different sizes). The value will be the same for both HSDPA and
Mobile WiMAX. The value of the total margin is 9 dB .
The same value of log-normal shadowing standard deviation will be used for both
technologies: 8 dB. [5], [27]
41
3.1.3 Path loss model
Path loss models are used to predict the path loss or power attenuation of a signal
traveling from a transmitter to receiver. The simplest path loss model is the free space
model, which describes the loss in signal strength when the signal travels through free
space where there are no obstacles. The power loss is proportional to the square of the
frequency of the signal and the square of the distance between the transmitter and
receiver. Equation (1) describes the free space path loss:
L= (4* *r/ )^
2
= 32.4 + 20*log(r) + 20*log(f) (1)
where:
: Is the signal wavelength
f: Carrier frequency
r: The cell radius (distance between transmitter and receiver)
The free path loss model cannot be used in most practical situations. Instead empirical
models based on measurements and observations in real propagation environments are
used.
We will consider two different path loss model for our systems, both models predict
mean path loss as a function of various parameters, such as the cell radius, antenna height
and environment considered. Same values will be used for both the HSDPA and Mobile
WiMAX systems everywhere possible. The environment, the antenna heights, the
reference distance d 0 have the same values. The only parameters that will not have the
same values are the carrier frequency, f c , and the frequency correction term (in Erceg).
COST 231-Hata
The first model considered is one of the most widely used path loss models, the COST
231-Hata model. This is a model that extends the Okumura-Hata model to cover a wider
range of frequencies.
The formula for this model is given by:
L=46.3+33.9log(f c )-13.82log(hb )+Alog(r)-B + G
Where:
A = 44.9-66.5log(h b ),
B =(1.1*log(f c )-0.7)*(hm )-(1.56*log(fc )-0.8) (for small to medium cities)
G= 0 dB (for medium sized cities and suburban areas, would be 3 dB for metropolitan areas)
f c : Carrier frequency
h b : Height of BS antenna
h m : Height of MS antenna
r: The cell radius
L: Sum of all gains and losses from the receiver to the transmitter.
42
This model is valid for medium to small size cities, for frequencies around 2 GHz and
antenna heights between 30m-200m (BS) and 1m-10m (MS). [8, page 85-87]
Erceg
Another well known model is the Erceg model.
The path loss model is derived from
experimental data collected by AT&T Wireless Services across the United States in 95
existing macro cells at 1.9 GHz. The model is for suburban areas, and it distinguishes
between three different terrain categories. The model applies to base station antenna heights
from 10 to 80 m, and distances from 0.1 to 8 km. [28]
The formula for this model is given by:
L = Ld0 + 10*n*log(d/d 0 ) + Xf + X h + s (3)
where
Ld0 is the free space path loss at d 0 ,
d 0 = 100 meters,
n is the path loss exponent,
d is the distance in meters,
Xf is the frequency correction term,
Xh is the receive antenna height correction term, and
s is the shadow fading component.
The formula to calculate the path loss exponent n is:
n = a - b* hb + c/hb (4)
To calculate the frequency correction term we use:
Xf = 6 * log (f c /2000) (5)
Where a,b and c are constants that represent different terrain categories. The
values of a, b and c for the different categories can be seen in Table 7.
Model parameter Category A
(Hilly, heavy trees)
Category B
Category C
(Intermediate)
(flat, few trees)
a 4,6 4 3,6
b 0,0075 0,0065 0,005
c 12,6 17,1 20
Table 7. Model Parameters.
To calculate the receive antenna height correction term we have:
X
X
= -10.8* log (h m /2000) (for category A and B) (6)
= -20* log (h m /2000) (for category C) (7)
h
h
43
In our calculations the following values will be used in the path loss models:
Height of BS antenna, h b : 30 m
Height of MS antenna, h m : 2 m
Shadow fading component: 8 dB
3.1.4 Link Budget
A link budget is where all gains and losses that a signal will experience while traveling
between a transmitter and receiver are listed and summed up to find the received power
when the transmitted power is given. Attenuation of the transmitted signal due to
propagation, antenna gains, penetration losses and implementation losses are examples of
losses and gains that are included in a link budget. Margins because of interference,
fading and penetration loss (indoor coverage) are also taken into account.
Later we will use the Link Budget to find the maximum allowable path loss (MAPL).
That is how much loss a signal can experience but still be detected at the receiver. This
parameter will than help us find the cell radius.
44
HSDPA Mobile WiMAX
Mobile WiMAX
(5 MHz)
Transmission Power (dBm) 24 23 23
Tx antenna gain (dBi) 0 0 0
Tx loss (dB) 1 1 1
EIRP (dBm) 23 22 22
Penetration loss (dB) 15 15 15
Fading Margin (dB) 9 9 9
Interference Margin (dB) 3 3 3
Total Margin (dB) 27 27 27
Rx antenna gain (dB) 18 18 18
Subchannelization gain (dB) 0 12 15
Processing gain (dB) (17,8) 0 0
Rx loss (cable loss in BS) (dB) 3 3 3
Rx signal strength (dBm )
Table 8. Uplink link budget
45
11 (28,8) 22 25
(10 MHz)
Parameter HSDPA Mobile WiMAX
(5MHz)
Mobile WiMAX
(10MHz)
Transmission Power (dBm) 43 41 41
Tx antenna gain (dBi) 18 18 18
Tx loss (dB) 3 3 3
EIRP (dBm) 58 56 56
Penetration loss (dB) 15 15 15
Fading Margin (dB) 9 9 9
Interference Margin (dB) 3 3 3
Total Margin 27 27 27
Subchannelization gain (dB) 0 0 0
Processing gain (dB) 12 0 0
Rx loss (dB) 1 1 1
Rx signal strength (dBm ) 42 28 28
Table 9. Downlink link budget
•
Transmission power: According to our references the output power for both
base station and mobile station is slightly lower for Mobile WiMAX than for
HSDPA. In the downlink the difference in the numbers we have assumed is 2 dB
but in the uplink 1 dB. HSDPA’s advantage is possibly because the HSDPA
equipment has been tested and developed longer and further than the WiMAX
equipment. [5, table 10], [10, page 148], [29], [30]
•
Antenna gain : In our link budget we have assumed that both HSDPA and
Mobile WiMAX will have antenna gains of 18 dBi. This assumptions were made
after looking at for example the following references: [5, table 10], [10, page
130], [30]
•
Tx loss: Is the cable loss in the base station in the case of the downlink and the
body loss at the terminal in case of the uplink. We have assumed same values
for both technologies, 3 dB in the downlink and 1 dB in the uplink.
•
EIRP (the effective isotropic radiated power) : can be found by using the
following equation:
EIRP = Tx Power (dBm) + Antenna Gain (dBi) - Implementation loss (dB)
And is the amount of power that would have to be emitted by an isotropic antenna
to achieve the peak power density in the direction of maximum antenna gain.
46
•
Penetration Loss: Is the loss the signal experiences when it travels through walls
and is added to the link budget to allow for indoor coverage. This value, 15 dB is
a typical assumption that applies to both technologies. It is assumed that 70 % of
the users are indoors and thus experience penetration loss.
•
Fading Margin : We have chosen to use total fading margin of 9 dB for both
technologies. This margin accounts for both multipath fading and shadowing. An
explanation of fading margins was given in chapter 3.1.2.
•
Interference Margin : In WCDMA systems the interference margin is needed
because of the loading of the cell, the load factor. The more load that is allowed
in the cell the larger interference margin is needed. In IEEE 802.16e the
interference margin is needed because of cochannel interference.
Margins
quoted for both technologies are typically around the standard 2-3dB. Hence we
assume the interference margin to be equal for both technologies, 3 dB
(corresponding to 50% load). [27]
•
Subchannelization gain : For 5 MHz bandwidth in OFDMA, we have 512
subcarriers organized into 17 different sub-channels. We can concentrate the
available power into one sub-channel, therefore gaining a factor of 17, which is
about 12 dB compared to single carrier systems [13]. For 10 MHz bandwidth
there are 1024 subcarriers organized into 34 subchannels. When all available
power is concentrated into one subchannel the gain is of factor 34 or 15 dB. This
applies only to the uplink. (See subchannelization chapter)
•
Processing gain : As discussed in chapter 2.2.2. in CDMA (and all spread
spectrum systems) systems the length of the spreading code determines the
spreading factor or how much the signal can be spread. This in turn determines
the Processing Gain or the ratio of the spread bandwidth to the unspread
bandwidth. The HS-DSCH channel uses a fixed spreading factor 16. Which
means that the processing gain is 12 dB. If we assume a non-real-time 384 kbps
data service in the uplink we will have processing gain: 10*log (3840/384) = 10
dB.
A 12,2 kbps data rate give processing gain: 10*log(3840/12,2) = 25 dB.
A 64 kbps data rate gives processing gain 10* log(3840/64) = 17,8 dB
•
Rx loss : Is the cable loss in the base station in the case of the uplink. In the case
of the downlink it is the loss experienced when the terminal (UE) is close to the
user’s head. In UMTS this is called body loss. We have assumed same values for
both technologies, 1 dB in DL in 3 dB in uplink.
47
3.1.5 Other system characteristics
HSDPA
A dedicated HSDPA network
The HSDPA system is assumed to be HSDPA-only system. That is the channels are used
for HSDPA traffic only and no R’99 traffic. This is usually not the case in UMTS
systems but as we are comparing throughput and coverage of HSDPA and Mobile
WiMAX which both only consider packet switched traffic the results will be more
comparable if the HSDPA traffic gets all the resources of the network instead of having
to share them with R’99 traffic.
User Equipment
Like we saw in Table 3, in chapter 2.2.3. there are 12 different UE categories for
HSDPA. In our calculations we will assume that all UEs support 15 HS-PDSCH codes
and 16-QAM modulation and can reach peak data rate of 10.2 Mb/s.
Duplexing method and cell configuration
The duplexing method used in the HSDPA network is FDD and thus we have paired
frequency bands. Each channel has 5 MHz for downlink and 5 MHz for uplink, each cell
has three sectors which each have their own channel. The total frequency allocation is
thus 30 MHz.
Mobile WiMAX
Duplexing method and cell configuration
For Mobile WiMAX, two types of systems will be considered. Both will use TDD as
duplexing method and thus the same channel will be used for both uplink and downlink.
The channel will be used for downlink transmissions 2/3 of the time and for uplink
transmissions 1/3 of the time.
The first system will have 5 MHz channel bandwidth and thus the total bandwidth of
each cell will be 15 MHz (3 sectors per cell). The second system will have 10 MHz
channel bandwidth and thus 30 MHz total bandwidth.
In Table 10 a list of the common system parameters is given. Those values were chosen
by comparing a few references and should be quite typical values for mobile radio
networks. [5], [27], [25], [29], [30]
48
Com mon system parameters
Channel bandwidth
5 MHz (and 10 MHz for WiMAX)
Cell configuration
3 sector/cell
BS Antenna height
30 m
MS Antenna height
2m
BS Antenna Gain
18 dBi
MS Antenna Gain
0 dBi
Area Coverage Probability
95%
Standard Deviation (log-normal shadowing)
8 dB
Penetration loss
15 dB
FadingMargin
9 dB
Interference Margin
3 dB (50% load)
Path loss Model
Cost 231 Hata / Erceg
Table 10. Common system parameters for HSDPA and Mobile WiMAX.
The system parameters that are different for the two technologies can be seen in Table 11.
System Parameters HSDPA Mobile WiMAX
Frequency
2000 MHz 2500 MHz
Duplexing method
FDD TDD, DL/UL =3:1
BS transmitted power
43 dB 41 dB
MS transmitted power
24 dB 23 dB
Modulation schemes
16QAM/QPSK 64QAM/16QAM/QPSK
Subchannelization gain (UL)
Does not apply 12 dB (5MHz)
15 dB (10MHz)
Processing gain
12 dB DL and 17,8 dB UL Does not apply
Nr. of HS-PDSCH codes
5,10 and 15 Does not apply
Table 11. System specific parameters
49
Modulation scheme and coding rate: Higher order modulation schemes can improve
data rate when the radio conditions are good. HSDPA supports QPSK and 16QAM.
Mobile WiMAX supports QPSK, 16QAM, 64QAM in DL and QPSK, 16QAM in UL.
Both technologies support both turbo coding and convolutional coding and both use
adaptive modulation and coding which means that the modulation scheme and coding is
changed on a per-user basis depending on signal quality and cell usage.
3.2 Network Dimensioning
3.2.1. Coverage planning
To find the cell radius, r, the path loss model is rearranged and the equation is solved for
r. Equation (7) shows how the COST-231 Hata model has been rearranged to solve for r:
r = 10^((L+B-46.3-33.9log(f c )+13.82log(hb ))/A) (7)
The only parameter that is still not known in equation (7) is L, the maximum allowed
path loss.
To find L we first find the minimum signal that the receivers can detect, the
Rx
sensitivity and the Rx signal strength.
L = Rx signal strength - Rx sensitivity
The Rx signal strength can be taken straight from the link budget calculations in chapter
3.1.4. In the chapter we have calculated the Rx signal strength for both the uplink and the
downlink. It is the limiting link that we will have to choose for the coverage planning.
Therefore it is the uplink Rx signal strength that we will use to calculate the cell radius.
To find the Rx sensitivity we need to know the SINR values at the receivers. For
Mobile WiMAX these values are defined in the IEEE 802.16 standards for different MCS
as in Table 12 below. For the HSDPA network we have in the downlink, different data
rates for different MCS levels but need to find the SINR values for each of those. To do
that we use that simulation results have showed that the performance of the HS-DSCH
channel is quite close to the Shannon limit of error-free data rate that can be transmitted
with a specified bandwidth in the presence of noise and interference. We thus use the
Shannon boundary shifted by 5 dB to find the SINR values for specific data rates. To do
that we use the following equation:
R=B*log2 (1+SINR/a) (8)
where a=3,16 (5dB).
The results can be seen in Table 12.
50
MCS WiMAX, SNR (dB) HSDPA
QPSK 1/2
5 4,6
QPSK 3/4
8 7,04
16QAM 1/2
10,5 9,23
16QAM 3/4
14 12,7
64QAM 1/2
16
64QAM 3/4
20
Table 12. SINR for different MCS levels, IEEE 802.16e [24], [31]
We will now find the receiver sensitivity for both technologies
Rx sensitivity, HSDPA
To calculate the Rx sensitivity we will use the following equation:
Sin = KTB RF (dBm) + SINR(dB) - PG(dB) + NF (dB)
(9)
where:
NF: Receiver noise figure, referenced to the antenna port. The assumed values
are
4 dBfor the BS and 7dB for the MS.
KTB
:
RF
K = Boltzmann's constant = 1.381 10-23 W/Hz/K,
T = 290K at room temperature and
B
= RF carrier bandwidth (Hz)
RF
So this will be -174dBm + 10*log(3.84MHz) =
-108.1 dBm
SINR: Signal to interference plus noise ratio, for downlink see Table 12 for the
uplink the assumed value is
4.6 dB .
P.G: Processing gain,
17,8 dB for uplink, 12 dB for downlink.
references: [10],[32], [33], [34]
For QPSK modulation and effective rate of 1/2 the SINR is 4,6 dB and by using equation
(9) we get:
Rx sensitivity, HSDPA = (-108,1dB) + 4,6 dB -17,8 dB + 4 dB =
The HSDPA Rx sensitivity for other MCS can be seen in Table 13.
51
-117,3 dB
Mobile WiMAX
We use the following equation to find the Rx sensitivity:
Rss = -114 +SNR RX -10log(R)+10log(F s *Nused /NFFT ) + NF(dB) (10)
Where: -114 = -174 + 10*log(5Mz)
NF: Receiver noise figure, referenced to the antenna port. The assumed values
are
4 dBfor the BS and 7dB for the MS.
R: The repetition factor (We will only consider the case of R=1)
Fs: The sampling frequency in MHz (5.6 and 11.2)
N
Number of used carriers (421 and 841)
used:
N
FFT size (512 and 1024)
FFT:
references: [35], [36], [37]
For bandwidth of 5MHz, QPSK modulation and effective rate of 1/2 we get the
following:
Rss (QPSK 1/2) = (-114) +5dB+6,6 dB +4 dB = -98,4 dB
The mobile WiMAX (5MHz and 10MHz) Rx sensitivity for the different MCS levels can
be seen in Table 13 and in Table 14.
QPSK 1/2 QPSK 3/4 16QAM 1/2 16QAM 3/4
-117,3 -114,9 -112,7 -109,2
Rx Sensitivity (dBm)
Table 13. HSDPA Rx sensitivity for different MCS levels. [27]
QPSK
1/2
Rx Sensitivity (dBm)
QPSK
3/4
16QAM
1/2
16QAM
3/4
64QAM
1/2
64QAM
3/4
-98,4 -95,4 -92,9 -89,9 -87,4 -83,4
BW=5MHz
Rx Sensitivity (dBm)
-95,4 -92,4 -89,9 -86,4 -84,4 -80,4
BW=10MHz
Table 14. Rx sensitivity for mobile WiMAX (5 and 10 MHz). [24], [38], [31].
Now that we know both the Rx signal strength and the Rx sensitivity we can calculate L,
the maximum allowed path loss. Below we show how we calculate L for both
technologies and outdoor only coverage:
52
HSDPA: MAPL = Limiting Rx signal strength - Rx sensitivity = 12 dB - (-117,3 dB) =
128,4 dB
Mobile WiMAX (5 MHz):
Mobile WiMAX (10 MHz):
MAPL = 22 dB - (-98,4) =
MAPL = 25 dB - (-95,4) =
120,4 dB
120,4 dB
And now we can use equation (7) and the corresponding equation for Erceg to find the
cell radius.
The results are listed in Table 15 where the cell radius of both systems, for both Erceg
and COST-231 Hata path loss models, and for both outdoor only coverage and
indoor4 coverage can be found. For the indoor coverage it has been assumed that 70 % of
the users are indoor and 30 % are outdoor.
Technology and path loss model Cell radius, outdoor
(0dB penetration loss)
Cell radius, indoor
(15 dB penetration loss)
HSDPA, COST-231 Hata 1800m 700m
HSDPA, Erceg (terrain B) 2300m 1000m
WiMAX (5MHz), COST-231 Hata 900m 300m
WiMAX (5MHz), Erceg (terrain B) 1300m 600m
WiMAX (10MHz), COST-231 Hata 900m 300m
WiMAX (10MHz), Erceg (terrain B) 1300m 600m
Table 15. Cell radius, for HSDPA and Mobile WiMAX (5 MHz and 10 MHz).
Coverage planning conclusions
We have designed a system for fixed, nomadic and mobile users that can be situated
outside or inside.
The total difference between HSDPA and mobile WiMAX in the maximum allowable
path loss in the uplink (which determines the cell radius) is 8 dB. This 8 dB difference
and the lower carrier frequency, which has better propagation characteristics, results in a
400 m longer cell radius for the HSDPA system. The 8 dB difference in downlink path
loss is because of HSDPA’s higher transmission power and because of the 17,8 dB
processing gain. OFDMA offers no processing gain but instead there is a
subchannelization gain of 12 dB in the case of a 5 MHz channel and 15 dB in the case of
a 10 MHz channel. The processing gain is related to the data rate that the channel uses, a
lower data rate gives a higher processing gain. Here we have assumed an uplink channel
with data rate 64 kbps which results in 10*log(3840/64) = 17,8 dB processing gain. 64
kbps is not a very high data rate, if we had chosen for example data rate of 384 kbps the
PG would have been 10 dB and then the two systems would have had approximately the
same cell radius.
4
By indoor coverage it is meant that connectivity is at least provided within outer walls of buildings,
wherefore a signal attenuation of approximately 15 dB is allowed for in the received signal strength.
53
3.2.2. Capacity planning
When planning the capacity the downlink is the much more important link. Here we
don’t consider the uplink at all, except that we use the maximum cell range found by
using the uplink budget in chapter 3.2.1. It is the cell range when designing for indoor
coverage that is used, that is 600m and 1000m for mobile WiMAX and HSDPA
respectively.
To calculate the average throughput we assume an isolated cell with evenly distributed
users. We first calculate the fraction of the coverage area that will have acceptable power
levels for each MCS. As a higher modulation and coding scheme demands a higher SNR
and thus the maximum allowable path loss will be lower for higher MCS.
To find the fraction of the cell where each MCS has acceptable power level we assume
lognormal fading centered around the selected threshold level and that the cell is a circle
with radius R, and y is the acceptable power level. Then P(Pr(R)>y) is the likelihood of
coverage at the boundary. By integrating the probabilities over the cell we get the
fraction of area where the power levels are acceptable.
U = 1/2(1-erf(a) + exp((1-2ab)/b 2 ) [1-erf((1-ab)/b])
(11)
where:
a=(y-P,(R))/ st.dv.*sqrt(2)
b = 10*path loss exp. *log(exp)/st.dev*sqrt(2)
reference [39]
To get the best average throughput the highest MCS is used everywhere within its range,
then the next highest MCS will be used inside its range except where the highest MCS
will be used and so on. This will give us the distribution of MCS levels which in turn will
give us the average throughput when we have multiplied the date rate of each MCS with
the portion of the cell where it is used.
For HSDPA the distribution of MCS levels can be seen in Table 16 and Figure 4.
QPSK, 1/2 QPSK, 3/4 16QAM, 1/2 16QAM, 3/4
Area coverage
probability
99,78% 99,49% 98,97% 97,24%
Distribution of
MCS
0,29% 0,52% 1,74% 97,45%
Table 16. Distribution of modulation and coding schemes, HSDPA.
54
Distribution of MCS, HSDPA
QPSK, 1/2;
0.29%
QPSK, ;
0.52% 16QAM, 1/4;
1.74%
16QAM,
3/4; 97.45%
Figure 4. Distribution of MCS, HSDPA
QPSK 1/2 QPSK 3/4 16QAM
1/2
16QAM
3/4
Area
coverage
probability
97,83% 95,34% 91,90% 84,42% 78,69% 64,58%
Distribution
of MCS
2,55% 3,52% 7,64% 5,86% 14,42% 66,01%
64QAM
1/2
64QAM
3/4
Table 17. Distribution of modulation and coding schemes, mobile WiMAX 10 MHz.
Figure 5. Distribution of MSC for WiMAX 10 MHz.
55
QPSK
QPSK
3/4
1/2
16QAM1/2 16QAM3/4 64QAM1/2 64QAM
3/4
Area coverage
probability
97,83% 95,34% 91,90% 91,03% 86,90% 75,45%
Distribution of
MCS
2,55% 3,52% 0,89% 4,22% 11,70% 77,12%
Table 18. Distribution of modulation and coding schemes, mobile WiMAX, 5 MHz.
Distribution of MCS, mobile WiMAX 5 MHz
QPSK, 1/2;
2.55%
QPSK, ;
3.52% 16QAM, ;
0.89%
16QAM, 3/4;
4.22%
64QAM, ;
11.70%
64QAM, ;
77.12%
Figure 6. Distribution of MCS for mobile WiMAX 5 MHz
In Tables 19 and 20 the peak data rates for the different modulations and coding rates are
given.
QPSK
1/2
QPSK
3/4
16QAM
1/2
16QAM
3/4
64QAM
1/2
64QAM
3/4
3,57 5,36 7,14 10,71 14,09 16,07
Peak data rate
(Mb/s)BW=5MHz
Peak data rate
(Mb/s)
7,14 10,71 14,28 21,42 21.42 32,14
BW=10MHz
Table 19. WiMAX, peak data rates for different modulation and coding schemes.
QPSK 1/2 QPSK 3/4 16QAM 1/2 16QAM 3/4
Peak data rate
(Mb/s)
3,6 5,3 7,2 10,7
Table 20. HSDPA peak data rates for different modulation and coding schemes.
56
Average throughput:
HSDPA: 10.7 * 0.974 + 7.2 *0.017 + 5.3*0.005 + 3.6 * 0.003 =
WiMAX 5MHz: 16.07 *0.771 + 14.09*0.117 +... =
14.44 Mb/s
WiMAX 10MHz: 32.14 *0.660 + 21.42 *(0.144+0.059) +14.28
*0.076+10.71*0.035+7.14*0.025 = 27.21 Mb/s
10.59 Mb/s
Once the average throughput per sector and the cell range has been found, we can find
the aggregate dowlink traffic that each base station can support. We have assumed three
sector sites for both technologies and the base stations used are 3 sector base stations
hence to find the throughput per site/base station the sector throughput is multiplied with
3. For Mobile WiMAX we first have to multiply the DL average throughput with 2/3 as
the channel is used for DL 2/3 of the time and UL 1/3 of the time.
Aggregate DL thoughput per site:
HSDPA:
3 * 10.59 =
31.77 Mb/s
Mobile WiMAX 5 Mhz: 14.44 Mb/s *2/3 * 3 =
28.88 Mb/s
Mobile WiMAX 10 Mhz: 27.21 Mb/s *2/3 * 3 =
54.42 Mb/s
As long as the simultaneous traffic demand per base station is less than the calculated
total downlink capacity per base station the system is coverage limited. When the
simultaneous traffic exceeds that capacity the system becomes capacity limited and new
base stations need to be added.
Capacity planning conclusions
For HSDPA we see that 97.45% of the users get the highest MCS which gives the highest
peak data rate, 10.7 Mb/s. This happens as there is a big difference in the downlink and
uplink link budgets. The uplink maximum allowable path loss is 10.2 dB less than the
downlink maximum allowable path loss.
It is the uplink that is the limiting link and decides the cell radius. However as the
downlink cell radius could be much bigger if we didn´t have to worry about the uplink we
loose all users outside a small radiusthat would be included in the cell if the uplink
limitation wouldn’t apply. Hence it turns out that only users that are so close to the base
station that they get the best modulation and coding scheme are included in the cell.
For the WiMAX cases the difference in uplink and downlink link budgets is not as big.
Hence the distribution of modulation schemes (Table 17) is more even. But the radius is
still relatively small and a high percentage of users (77% for 5 MHz and 66% for 10
MHz) get the highest bit rate.
57
4. Techno economic analysis
4.1 Tool
To carry out the techno economic analysis we will use a spreadsheet based model that
was created by Telenor 5 and used in the Eurescom project that this study is partly based
on. The model was created originally to calculate the economical feasibility of a few
different Mobile WiMAX Business Cases.
This tool was chosen for several reasons. First of all it fits the purpose of this thesis
perfectly as it gives us the outputs we are looking for and considers all input parameters
that we are interested in. It is available for us to use and is straightforward and easy to
alter to fit our needs.
4.2. Inputs to the techno-economic analysis
In this chapter the input parameters of the techno economic analysis tool will be listed
and the values that will be used in this paper given. When choosing those values the
most important thing for the purpose of this thesis was to make it the same values for
both technologies everywhere possible, as it is the comparison we are after. Therefore
we chose to use mostly all the same input data as was used in the Eurescom study. The
HSDPA specific information, like HSDPA equipment cost and frequency license fee was
either provided by Síminn or obtained from official documents.
The deployment scenario
For the purpose of a simple comparison the scenario of a new entrantis the scenario
chosen for both technologies. That is the operator has no previous customers and no
previous network and will use mobile WiMAX/HSDPA as the only technology to
compete with other operators.
All customers are stand-alone customers, that is they don’t buy any other services from
the operator.
The following coverage rollout is assumed:
First year of deployment: 30 % coverage
Second year of deployment: 60 % coverage
Third year of deployment: 100% coverage
Population and area size
This data is exactly the same for both mobile WiMAX and HSDPA. The geographic area
is Reykjavík and its neighboring communities, with population of about 200.000 and area
of 500 km2 . [40]
5The model was created by Arild Jacobsen, Borgar Olsen and Markku Lähteenoja at Telenor R&D
58
Number of Customers, penetration levels
In Table 21 a prediction of how the mobile broadband market will develop in the next 10
years is shown. The prediction is both for the whole broadband market with all
technologies included and for HSDPA and mobile WiMAX specifically. The numbers
that show the number of users for HSDPA and mobile WiMAX (applies regardless of
what bandwidth size has been chosen) is calculated for the city of Reykjavik with
approximately 200.000 inhabitants. The prediction was made by the authors of the
Eurescom study and was made for a European city with 1.600.000 inhabitants.
To predict how the new entrant will succeed in getting new customers in his first 10 years
it has been assumed that the saturation level of HSDPA is 50% of the total mobile
broadband market and for mobile WiMAX a 40 % saturation level. WiFi will have the
remaining 10 %.
Years 0 1 2 3 4 5 6 7 8 9 10
Total market share of
mobile broadband
10% 15% 23% 32% 42% 53% 65% 77% 86% 92% 96%
HSDPA market share 0,5% 1% 2% 4% 8% 14% 23% 31% 39% 44% 47%
Nr of HSDPA users 1000 2058 4187 8333 15903 28230 45000 62989 77974 88043 93871
WiMAX market share 0% 1% 2% 3% 6% 11% 18% 25% 31% 35% 38%
Nr of WiMAX users 800 1664 3350 6667 12722 22584 36000 50391 62379 70435 75097
Table 21. A prediction of the mobile broadband market
In our comparison we have however considered two cases of how the penetration levels
will look like. In the first case we have chosen to use the same nr of users (or penetration
levels) for both technologies. The reason for this is that it is quite hard to make a
predictions of this kind and they will have large error margins. As this thesis does not
focus on market aspects but rather technological differences this is the case used when
comparing the business cases in chapter 5. The second case uses the prediction shown in
Table 21 and the difference in NPV when using case 1 or case 2 can be seen in Figure 13
in chapter 5.3.
59
Installation and site cost
Most of the base stations will be on new sites, or 70 % and 30 % will be co-sited with
other operators’ sites. Table 22 lists all the installation and site cost.
Price in Euros
Installation cost for co-siting
6,000
Installation cost for a new site
50,000
Annual site rental co-siting
3,000
Annual site rental new site
6,000
CPE installation cost (operator)
250
CPE installation fee (paid by subscriber)
250
Table 22. Installation and site cost.
Subscription Types
In the model two types of subscriptions are defined:
Stand-alone subscription (new customers or customers taken from other providers).
Add-on subscription.
For a new entrant all subscriptions are stand-alone as there are no previous customers.
Three classes of subscriptions (Gold, Silver, Bronze) are also defined with different
tariffs (monthly flat rate) and different data rates.
ARPU (Euro per month) for
Data rate
stand-alone customers
Gold
50 2
Silver
40 1
Bronze
30 0,5
(Mb/s)
Table 23. ARPU (Average Revenue/User) and data rate for 3 subscription types.
[4]
A constant distribution of Gold (20%), Silver (60%) and Bronze (20%) customers is
assumed.
60
Network dimensioning
For the network dimensioning the results from chapter 3 will be used. We use the cell
radius found when using the Erceg model and designing for possible indoor usage (15 dB
penetration loss).
HSDPA Mobile WiMAX
(5MHz)
Cell radius
1000m 600m 600m
Cell throughput
31.77 Mb/s 28.88 Mb/s 54.42 Mb/s
Mobile WiMAX
(10MHz)
Table 24. Cell radius and average throughput
Maximum number of simultaneous users (busy hour): 60%
It is assumed that at busy hour up to 60% of the users can be active at the same time.
Contention rate: 5 % (1:20)
It is assume that the contention rate is 1:20 or 5 %. That is up to 20 users might have to
share the system bandwidth at any given time and still get the data rates they have paid
for (according to Table 23).
When the number of base stations needed in the network is calculated two requirements
have to be fulfilled. The whole service area needs to be covered (coverage) and the users
have to get the data rates they have paid for. To fulfill the first requirement we simply
divide the total area by the calculated cell area. In reality this would be too much of a
simplification and the base stations would need to be placed with users density,
geographic in mind.
Nr of BSs need for coverage: Area/cell area = 500 km
2
/ *(R cell )2
To fulfill the second requirement of capacity we first find what is the total bit rate
required of the system by multiplying the data rate of each subscription type with the
number of users of each subscription type:
Nr of users*(0.2*2 Mb/s + 0.6*1 Mb/s + 0.2*0.5 Mb/s) = Nr of users * 1.1 Mb/s
It is also assumed that the maximum number of simultaneous users (busy hour) is 60 %
and the contention rate is 5%. Hence the required capacity is:
Nr. of users*1.1 Mb/s *0.6 *0.5/BS throughput = Nr. of users * 0.33 Mb/s/BS throughp.
In Table 25 the number of BSs needed to fulfill both the coverage and capacity
requirements are shown for both HSDPA and WiMAX when it has been assumed that the
total number of subscribers is 40.000 or 20% of the total population for both networks.
61
HSDPA WiMAX 5 MHz WiMAX 10 MHz
Nr. of BSs needed for coverage
160 443 443
Nr. Of BSs needed for capacity
42 46 25
Number of BSs required
160 443 443
Table 25. Nr. of BSs needed to fulfill coverage and capacity requirements.
Cost assumptions
For WiMAX all equipment cost numbers is taken from the Eurescome study. In the case
of HSDPA Síminn has provided an estimation of the equipment cost. The frequency
acquisition costs for HSDPA are known official numbers and from those numbers we
made an estimation of what these costs could be for mobile WiMAX.
According to the cost assumptions we have used the mobile WiMAX base stations are
almost twice as expensive as the HSDPA base stations. This is probably because the
mobile WiMAX equipment is still in a developing phase while the HSDPA equipment is
more mature and has already been sold in big quantities. On the other hand the core
network cost is smaller for mobile WiMAX as it is much simpler than the quite
complicated architecture of an UMTS networks.
Backhaul : The traffic of a cellular network needs to be backhauled from its base stations
to a central point, like a RNC, MSC or a central server. This can be done in a few
different ways, for example by renting a leased line from the local incumbent, laying
optical fiber or using a microwave link.
Here the same backhaul solution is assumed for both technologies, a microwave link.
The OPEX costs include manpower costs for operations/maintenance, customer support
and sales/marketing. This ranges from 5 to 12 people. It also includes advertising costs
and OPEX variable cost (per customer per year).
Equipment cost
WiMAX BS of 3 sectors with 2nd order diversity in all sectors: 47.000
HSDPA BS of 3 sectors, 1 carrier frequency: 25.000
Core network costs
WiMAX, Radius server, routers, SIP server etc. 1.000.000
HSDPA: RNCs, MSC/VLR, SGS etc..
4.400.000
Frequency acquisition costs
WiMAX Frequency license acquisition cost (10 MHz): 2.000.000
WiMAX Frequency license acquisition cost (5 MHz): 1.000.000
Annual WiMAXfreq. license fee (10 MHz): 100.000
Annual WiMAXfreq. license fee (5 MHz):
50.000
HSDPA Frequency license acquisition cost:
2.000.000
62
Annual HSDPA frequency license fee:
100.000
Annual Microwave frequency license cost:
Backhaul
Microwave backhaul STM1 (155Mbit/s)
100.000
16.250
OPEX
OPEX variable cost
50
Salary cost including overhead
100.000
Installation cost for a new site
50.000
Site rental for a new site
6000
References: [2], [4]
4.3 Outputs from the techno-economic analysis
4.3.1 NPV, IRR and cash balance curve
Outputs from the techno-economic analysis
The techno-economic analysis will give results in terms the net present value (NPV), the
internal rate of return (IRR) and a graph of the accumulative cash flow (a cash balance
curve) for an investment project, as well as the OPEX, CAPEX and revenues for a period
of 10 years.
Net present value
The NPV is a measure of profitability and is defined as:
cash flows minus the initial investment . [41]
The present value of a project’s
In other words it is the difference between the discounted value of the future incomes and
the amount of the initial investment. A project with a positive NPV is a profitable
project.
Internal rate of return
The IRR is the discount rate that equates the present value of the project’s cash flows
with the initial investment, i.e. the interest rate that would make the NPV of a project
zero. A project that has an IRR that is greater than the required rate of return should be
accepted. When comparing projects the investment project with the highest IRR should
be chosen [41, page 249]
The discounting rate is set to 10% and the time period for calculating Net Present Value
(NPV) is set to 8 years.
Payback period and cash balance curve
Payback period is the time it takes to recoup an investment’s cost. That is the number of
years necessary for the accumulative cash flow to equal the investment cost.
63
From or model we will get the NPV, IRR and the cash balance curve for both the mobile
WiMAX and the HSDPA business cases. The NPV is given in Euros and the IRR in
percentages. An example of a cash balance curve is given below.
Figure 7. Example of a cash balance curve
The cash balance curve shows the accumulated cash flow for each year for some period
of years. The accumulated cash flow for the first year is the difference between the total
revenue and the TOTEX (CAPEX + OPEX). That is, what is left of the income when
everything else has been paid. The accumulated cash flow the second year is that years
cash flow plus the first years cash flow and so on.
The cash balance curve gives a graphical overview of the profitability. The lowest point
on the graph gives the total amount of funding needed for the project. The point where
the curve crosses the x-axes gives the payback period in years.
Capital expenditures (CAPEX) are the amount of money spent to acquire or upgrade
the physical assets of a business. In the case of a mobile broadband operator this includes
the base stations, the core network equipment, backhaul equipment, frequency licenses,
CPE equipment cost and site installation cost.
Operational expenditures (OPEX) are the ongoing costs of running a business. This
includes advertising, maintenance of the network, sales, manpower etc.
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5. Results
5.1. NPV, IRR and cash balance curves
In this chapter the results from using the spreadsheet based techno-economic analysis tool
described in chapter 4.1 are shown. The input parameters have all been listed in chapter
4.2.
Results
Discount rate 10%
Required investment capital ( ) -52 047 260
Lifetime 7 year
NPV ( ) IRR
-28 532 068
-8%
Lifetime 10 years
-4 094 340
9%
Table 26.Required investment capital, NPV and IRR for Mobile WiMAX 10 MHz
Results
Discount rate 10%
Required investment capital ( ) -50 847 260
Lifetime 7 year
NPV ( ) IRR
-27 238 647
-8%
Lifetime 10 years
-2 737 112
9%
Table 27.Required investment capital, NPV and IRR for Mobile WiMAX 5 MHz
Results
Discount rate 10%
Required investment capital ( ) -20 784 629
NPV ( ) IRR
Lifetime 7 year 3 605 235 14%
Lifetime 10 years 29 884 828 27%
Table 28.Required investment capital, NPV and IRR for HSDPA
Tables 26 to 28 show that HSDPAs NPV after 10 years is 29 884 828 while both
mobile WiMAX cases have negative NPV. Moible WiMAX that uses channels of 10
MHz bandwidth have NPV of -4 094 340 and the mobile WiMAX network that uses 5
MHz channels has NPV of -2 737 112 .
65
Figure 8. Cash balance curve for mobile WiMAX 10 MHz
Figure 9. Cash balance curve for mobile WiMAX 5 MHz
Figure 10. Cash balance curve for HSDPA
66
Figures 8, 9 and 10 show the accumulated cash flow of our business cases.
Other results
HSDPA
Total revenue: 156 001 677
Total CAPEX: 36 279 123
Total OPEX: 38 081 959
Total CAPEX + OPEX: 74 361 082
WiMAX 5 MHz
Total revenue: 156 001 677
Total CAPEX: 63 484 821
Total OPEX: 51 822 159
TOTEX (CAPEX + OPEX): 115 306 980
WiMAX 10 MHz
Total revenue: 156 001 677
Total CAPEX: 64 484 821
Total OPEX: 52 372 159
Total CAPEX + OPEX: 116 856 980
As we have here assumed exactly the same number of users for all our cases and same
ARPU all cases have the same total revenue. On the other hand HSDPA has lower
CAPEX and OPEX, and thus has a better cash flow.
5.2 Comparison
WiMAX 5 MHz vs WiMAX 10 MHz
NPV
IRR
TOTEX
Mobile WiMAX 5 MHz Mobile WiMAX 10 MHz
-2 737 112
-4 094 340
9 % 9%
115 306 980 116 856 980
Table 29.Comparison of WiMAX with 5 MHz bandwidth and 10 MHz bandwidth
As we see in Table 28 the business case where 5 MHz channels are used for mobile
WiMAX gives slightly better results in terms of NPV and IRR than the case where 10
MHz channels are used. But the difference is very small. The reason for this is that as
the system will be coverage limited for the whole time period of 10 years the cell radius
is much more important than the capacity. The channel bandwidth only affects the
67
capacity and not the coverage. The slightly better TOTEX of the 5 MHz system is
because of lower frequency license costs.
WiMAX vs HSDPA
Mobile WiMAX 5 MHz HSDPA
NPV
-2 737 112
29 884 828
IRR
9 % 27%
TOTEX
115 306 980 74 361 082
Table 30. Comparison of HSDPA and mobile WiMAX (5 MHz BW).
In Table 29 a comparison of the two cases HSDPA and mobile WiMAX (BW 5 MHz) is
given. We see that HSDPA has much better results and is thus by far the most feasible
choice from an economical perspective. The much lower TOTEX is mainly because of
the big difference in number of base stations needed to cover the whole area. In the case
of mobile WiMAX the number of base stations needed for coverage is 443 base stations .
For HSDPA the number is 160 base stations . This is an enormous difference, which
results in an enormous difference in economical feasibility as well.
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5.3 Sensitivity analysis
In chapter 5.3.1 we look at how different parameters affect the outcome of our business
cases. In chapter 5.3.2 we discuss how choosing the radio planning parameters and the
system model differently would have affected the results.
5.3.1 Business case sensitivity
The cell radius and cell throughput directly affect the economic calculations as they
determine how many base stations are needed to serve the area and hence a large part of
the whole infrastructure cost.
Cell radius
In Figure 11 it can be seen how the cell radius affects the NPVs (for 10 years lifetime) of
our business cases. We use the channel throughput calculated in chapter 3 (see Table
24) , that is different channel throughput for each case, and keep it constant.
Figure 11.Sensitivity on cell radius.
We see in Figure 11 that the curves for HSDPA and both WiMAX cases are all very
similiar. For the same cell radius the NPV of all the cases is close to being the same.
The curves all pass zero on the x-axis close to 0.6 km. Which means that for the
business cases to be feasible the cell radius needs to be larger than 0.6 km. A network
that has cell radius of 1 km will be a much more attractive from a business perspective
than a network with 0.6 km cell radius. But if the cell radius is extended from 1 km to
1.4 km or more the difference is not as drastic.
69
24.
Figure 12. Sensitivity on channel throughput
Figure 12 shows that the throughput has a minor effect on the NPV. Indeed, changes on
the scale, from 2 Mb/s to 20 Mb/s as shown in the figure, do not have any impact at all on
the WiMAX business cases. On the other hand if the channel throughput of the HSDPA
network would be decreased down to 2 Mb/s from the calculated average channel
throughput of 10.6 Mb/s the would NPV would be decreased by 64 %, from 29.884.828
Euros to 19.206.192 Euros. To increase the channel throughput to more than 10.6 Mb/s
does not increase the NPV if nothing else is changed.
The reason for that HSDPA NPV seems more sensitive to changes in channel throughput
than the WiMAX NPV is that we have used the calculated cell radiuses (1km for HSDPA
and 0.6 km for WiMAX ) This means that when the throughput is decreased the system
with longer radius (fewer cells and more users per cell) becomes capacity limited earlier.
70
71
.
.