Wireless Transmission
and Services
Objectives

Associate electromagnetic waves at different points on
the wireless spectrum with their wireless services

Identify characteristics that distinguish wireless
transmission from wire-bound transmission

Explain the architecture and access methods used in
cellular networks and services

Understand the differences between wireless and
wireline local loops
Objectives

Describe the most popular WLAN standards, including
their advantages, disadvantages, and uses

Identify the major satellite positioning schemes and list
several telecommunications services that rely on
satellite transmission
The Wireless Spectrum
http://www.fcc.gov/Bureaus/OPP/working_papers/oppwp38chart.pdf
The Wireless Spectrum
The Wireless Spectrum
Unlicensed Frequency
Bands
Characteristics of Wireless
Transmission
Antennas

Radiation pattern the relative strength
over a three
dimensional area of
all the
electromagnetic
energy the antenna
sends or receives.

Directional
antenna - issues
wireless signals
along a single
direction
Antennas

Omni-directional
antenna - issues and
receives wireless
signals with equal
strength and clarity in
all directions.
Signal Propagation

Reflection - the wave encounters an obstacle and
bounces back towards its source.

Diffraction - a wireless signal splits into secondary
waves when it encounters an obstruction.

Scattering - the diffusion, or the reflection in
multiple different directions of a signal.
Signal Propagation
Signal Propagation

Fading and Delay

Fading: a change in signal strength as result of
some of the electromagnetic energy being
scattered, reflected, or diffracted after being
issued by the transmitter.

Diversity - the use of multiple antennas or multiple
signal transmissions to compensate for fading and
delay.
Signal Propagation

Attenuation - after a signal has been transmitted,
the farther it moves away from the transmission
antenna, the more it weakens.

Interference - because wireless signals are a form
of electromagnetic activity, they can be hampered by
other electromagnetic energy, resulting in interference.
Narrowband, Broadband, and
Spread Spectrum Signals

Narrowband - a transmitter concentrates the
signal energy at a single frequency or in a very small
range of frequencies.

Broadband - a type of signaling that uses a
relatively wide band of the wireless spectrum.

Spread spectrum - the use of multiple
frequencies to transmit a signal.
Fixed vs. Mobile
Fixed vs. Mobile
Cellular Communications

Mobile telephone service - a system for
providing telephone services to multiple, mobile
receivers using two-way radio communication over a
limited number of frequencies.

Mobile wireless evolution:




First generation
Second generation
3G - Third generation
4G - Fourth generation (next)
Principles of Cellular Technology
Cells
Figure Radio frequency reuse for cellular towers
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Cellular Call Completion

Components of a signal:

MIN (Mobile Identification Number) - an enclosed
representation of the mobile telephone’s 10-digit telephone
number.

ESN (Electronic Serial Number) - a fixed number assigned
to the telephone by the manufacturer.

SID (System Identification Number) - a number assigned
to the particular wireless carrier to which the telephone’s
user has subscribed.
Cellular Call Completion
Mobile telephone switching office
Figure 10-4
Mobile Switching Office
BTS
BSC
BTS
BTS
BTS
BTS
Central Office
BSC – Base Station Controller
BTS – Base Transceiver Stations
BH – Backhaul
Call Completion
Figure 10-5
Figure 10-6
AMPS (Advanced Mobile Phone
Service)

A first generation
cellular technology
that encodes and
transmits speech as
analog signals.
TDMA (Time Division Multiple
Access)
CDMA (Code Division Multiple
Access)

Each voice signal is
digitized and assigned a
unique code, and then small
components of the signal
are issued over multiple
frequencies using the
spread spectrum technique.
GSM (Global System for Mobile
Communications)

A version of TDMA (time division multiple access) technology,
because it divides frequency bands into channels and assigns
signals time slots within each channel.

Makes more efficient use of limited bandwidth than the IS-136
TDMA standard common in the United States.

Makes use of silences in a phone call to increase its signal
compression, leaving more open time slots in the channel.
3G (Third Generation)
Technologies
In this emerging technology a user can access all
telecommunication services from one mobile phone.

CDMA2000 - a packet switched version of CDMA.
Maximum throughput is 2.4 Mbps.

W-CDMA (Wideband CDMA) - based on technology
developed by Ericson, is also packet-based and its
maximum throughput is also 2.4 Mbps.
WLL (Wireless Local Loop)

WLL is a generic term that describes a wireless link
used in the PSTN to connect LEC central offices with
subscribers.

Acts the same as a copper local loop.

Used to transmit both voice and data signals.
LMDS (Local Multipoint
Distribution Service)

A point-to-multipoint, fixed wireless technology that
was conceived to supply wireless local loop service in
densely populated urban areas to issue television
signals.

A disadvantage is that its use of very high frequencies
limits making its transmission distance to no more than
4km between antennas.
MMDS (Multipoint Multichannel
Distribution System)

Uses microwaves with frequencies in the 2.1 to 2.7
GHz range of the wireless spectrum.

One advantage is its lower frequency range, MMDS is
less susceptible to interference.

MMDS does not require a line-of-sight path between
the transmitter and receiver.
WLAN Architecture
WLAN Architecture
WLAN Architecture
Wireless Networking Standards

802.11 - IEEE’s Radio Frequency Wireless networking standard
committee.

802.11b - uses DSSS (direct sequence spread spectrum)
signaling. Uses the 2.4-2.5 GHz frequency range and separates
it into 14 overlapping 22-MHz channels – 11 mbps. Mbps 38
meters

802.11g - designed to be just as affordable as 802.11b while
increasing its maximum capacity from 11 Mbps through different
encoding techniques to 54Mbps. Mbps 38 meters

802.11a - uses multiple frequency bands in the 5 GHZ range.
Like 802.11g, 802.11a provides a maximum throughput of 54
Mbps 35 meters

802.11n - developed by the IEEE LAN/MAN Standards
Committee (IEEE 802) in the 5 GHz and 2.4 GHz public
spectrum bands. 300 Mbit/s (2 streams) 70 meters
Bluetooth

A mobile wireless networking standard that uses DSS
(direct sequence spread spectrum) signaling in the 2.4
GHz band to achieve a maximum throughput of less than
1 Mbps. Effective range up to 25 - 30 feet

Designed to be used on small networks composed of
personal communications devices, also known as PANs
(Personal Area Networks).
Personal Area Networks
Satellite Positioning

The original method for positioning satellites above the
earth was in GEO (geosynchronous orbit).

Geosynchronous satellites are positioned
approximately 35,800 km (22,300 miles) above the
earth’s equator.

An alternative to GEO satellites are LEO (low earth
orbiting) satellites.
Satellite Positioning
http://science.nasa.gov/realtime/jtrack/3d/JTrack3D.html
Satellite Services

Digital broadcasting - To deliver content to subscribers,
multimedia providers uplink their audio and video signals to a
satellite, which then downlinks the signals, in a broadcast
fashion, to earth.

Analog broadcasting - Traditional analog television and radio
signals can be issued from a terrestrial transmitter to a satellite
and then downlinked to another terrestrial location within
seconds.

Mobile Wireless - Services such as cellular telephone, paging,
and other PCS applications are well suited to LEO or MEO
satellite transmission.
Satellite Services

Tracking and monitoring - Two-way satellite communications
can be used to monitor the whereabouts and condition of wildlife,
mobile weather sensors, marine vessels, and so on anywhere in
the world.

GPS (Global positioning service) - A service that expands on
remote monitoring functions, GPS allows a mobile station on earth
to exchange signals with a satellite to determine its precise
location.

WANs (Wide area networks) - Private companies use satellite
transmission to connect multiple locations on their WANs.
Components & Technologies
46
Cisco Aironet 802.11b
Client Adapters
2.4 GHz
802.11b
11
Mbps
Include
PC
Card
PCI Card
LMC Card
Mini PCI
Example of wireless
adapter

5 GHz/802.11a
• 54 Mbps
Rate
Shifting
• 6, 9, 12, 18, 24, 36, 48, or 54
Fixed
data rates
• User configurable option

5 dBi Patch Antenna

CardBus interface

Transmit power settings:
• 20 mW, 10 mW, and 5 mW
Acoustical strength is measured relatively per the dBi scale.
WLAN Topologies

A typical use of wireless technology as an add-on to a
traditional LAN.

Building to building wireless connectivity can be more cost
effective and can avoid obstacles faced by wired connections.
WAN Solutions
Four main requirements for WLAN solution:
1.
2.
High availability
•
Through system redundancy
•
Redundant AP automatic rate negotiation
Scalability
•
using multiple APs per coverage area
•
using multiple frequencies
•
AP using load balancing
3.
Manageability (diagnostic tools)
4.
Open Architecture
•
802.11a
•
802.11b
Challenges & Issues
51
Interference from other
Sites
Since the 802.11 standards use unlicensed spectrum:

Interference cannot always be detected until the link is
actually implemented.

Changing channels is the best way to avoid
interference.
Power Management
Power consumption is always an issue with laptops.
There are 3 modes of power for Cisco PC cards:
1.Constant Awake Mode (CAM)
Mode is best when power is not an issue such as when AC
power is available to the device. Default mode
2. Power save mode (PSP)
Mode is used when power conservation is the utmost
importance. The wireless NIC card will go to ‘sleep’ after a
period of inactivity & periodically awake to retrieve buffered
data from the AP.
3. Fast power save mode (FastPSP)
Combination of CAM & PSP. For clients who switch between
AC & DC power.
Interference from other
Devices

Other devices use these frequencies.

Physical objects also cause interference.

In unlicensed bands, the potential for interference from
another unlicensed user is becoming greater. The
unlicensed bands are allocated on a shared basis.
Interoperability
 Interoperability
issues might influence an Admin
to use a single vendor for all wireless needs.
 Closed
networks, such as corporate sites, might
choose a single-vendor solution in order to
benefit from increased management utilities and
vendor accountability.
 In
an open network such as a college campus,
the admin cannot usually dictate hardware
selection, and must support a variety of
hardware solutions.
Network Security

As wireless networks grow, the threat of intruders from
the inside and outside is great. Attackers called war
drivers are continually driving around searching for
insecure WLANs to exploit.

IEEE Wired Equivalent Privacy (WEP) with Temporal
Key Integrity Protocol (TKIP) provides robust
authentication options with 802.1X to make 802.11based wireless LANs secure.

IEEE has adopted the use of the Advanced Encryption
Standard (AES) to the data-privacy section of the
proposed 802.11i standard.
Installation & Site Design
Issues
 Obstructions
to visual link:
Topographic
features
Curvature of the Earth
Buildings
Trees
Installation and Site Design
Issues—WLAN
HotSpots
Today hot spots exceed 220,000 (Oct 2008)
Wi-Fi Manufactures
• Intel – Wi-Fi chips
• Microsoft
• Cisco; 70% of wired computer networks
• 1999 bought Aironet Wireless Communications for
$800 million.
• 2003, paid $480 million for Linksys.
• is now the leading maker of Wi-Fi gear
•Netgear
Health Issues
In general, living things should not be subjected to RF
energy unnecessarily
Antenna guidelines
 Do not touch an active antenna.
 Do not stand in front of, or close to, an antenna that is
radiating a signal.
 Stand to the back or side of any dish-type antenna.
 Always assume that any antenna is currently
energized.
 Small-sized antennas operate at higher frequencies,
which are more potentially hazardous.
 Maintain at least 5 cm (2 in.) between yourself and a
laptop antenna.
Summary

The wireless spectrum, the range of frequencies within the
electromagnetic spectrum that are used for telecommunications
services, starts at 9 KHz and ends at 300 GHz.

Cellular telephone service is distinguished from other mobile
two-way radio services by its use of cells to reuse limited
frequencies within a certain geographical area.

WLANs (Wireless LANs) use the same protocols and a similar
architecture as wired LANs.
Your assignment
 What
is 802.20?
 What is its purpose?
 Where is it used ?
 Where is it now installed?
 How does it fit in with WiFi?
 What is its future?
Figure 10-1
Central Office
Figure 10-2 Radio frequency reuse for cellular
towers
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Figure 10-3
Figure 10-4
Mobile Switching Office
BTS
BSC
BTS
BTS
BTS
BTS
Central Office
BSC – Base Station Controller
BTS – Base Transceiver Stations
BH – Backhaul
Figure 10-5
Figure 10-6
Conclusion

Associate electromagnetic waves at different points on
the wireless spectrum with their wireless services

Identify characteristics that distinguish wireless
transmission from wire-bound transmission

Explain the architecture and access methods used in
cellular networks and services

Understand the differences between wireless and
wireline local loops
Conclusion

Describe the most popular WLAN standards, including
their advantages, disadvantages, and uses

Identify the major satellite positioning schemes and list
several telecommunications services that rely on
satellite transmission
END