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Digital Cellular Telephony
Chapter 8
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Learning Objectives
Describe the applications that can be used on
a digital cellular telephone
Explain how cellular telephony functions
List and describe the features of the
generations of cellular telephony
List and describe the four types of client
software used on a digital cellular telephone
Discuss the issues surrounding 3G
implementation
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Digital Cellular Telephony
Although commonplace, digital cellular
telephony is most competitive and complex
of all wireless telephony
Variety of competing technologies such as
GSM and CDMA2000 1XEVDO rather than
single standard
Competing carriers each push a specific
technology
Governments have even auctioned off part of
wireless spectrum to highest bidder
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Applications
New and expanded features and applications
are pushing wireless digital cellular networks
beyond just voice communications
Digital cellular telephony can be used for
Internet access, e-mail, video conferencing,
and running a variety of programs
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Short Message Services
(SMS)
Short Message Services (SMS) delivers
text-based messages up to 160 characters
directly between wireless devices without
using the Internet
SMS is popular in Europe and Japan with over
200 billion messages sent annually
SMS is slow in reaching the US because of
profusion of other wireless digital alternatives
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How Cellular Telephony
Works
Two keys to cellular telephone networks
Coverage area is divided into cells, each with a
cell transmitter connected to base station that, in
turn, is connected to mobile telecommunications
switching office (MTSO)
See Figure 8-1
All the transmitters and cell phones operate at
low power level to prevent signals from
interfering with other cells that may use same
frequencies
See Figure 8-2
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Cellular Network
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Frequency Reuse
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Cellular Telephone Codes
Special codes are associated with cell
phones
Codes identify phone, phone’s owner, and
carrier or service provider
Table 8-1 summarizes the codes
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Cellular Telephone Codes
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Cellular Telephone
Handoffs and Roaming
When telephone user moves within same cell, base
station handles transmissions
Handoff is when user moves to another cell and is
automatically associated with base station of that
cell
Roaming is when user moves beyond coverage area
of entire cellular network into remote area, as seen
in Figure 8-3
Network in remote area contacts home network to
verify that user can make calls and is charged
appropriately
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Handoff and Roaming
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How a Cellular Phone
Receives a Call
Cell phone listens for SID transmitted by
base station on control channel
If SID matches that programmed into
phone, cell phone transmits registration
request to base station that MTSO uses
If SID does not match, cell phone is
roaming and MTSO of remote network
contacts MTSO of home network to confirm
SID is valid
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How a Cellular Phone
Receives a Call
MTSO locates phone and selects frequency
which is sent to phone over control channel
As user moves to edge of cell, base stations
coordinate through MTSO and instruct
phone to change frequencies as it is handed
off to another cell
See Figure 8-4
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Receiving a Call
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Digital Cellular Telephony
Existing since the early 1980s in the United
States, cellular telephony is divided into
several generations
First Generation
Second Generation
2.5 Generation
Third Generation
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First Generation
1G uses analog signals and has 9.6 KHz
maximum transmission speed
Based on Advanced Mobile Phone Service
(AMPS), 1G uses 800-900 MHz frequency
Each channel is 30 KHz wide with 45 KHz
passband
832 frequencies are available, with 790 used
for voice traffic and 42 for control channel
These freq. are split between two players in
each market
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First Generation
AMPS uses Frequency Division Multiple Access
(FDMA), as illustrated in Figure 8-5
User is allocated single channel at a time and
is switched to another channel if original one
deteriorates or has interference
1G networks use circuit-switching technology
Because analog signals are prone to interference,
1G is used basically for voice
It has been replaced with improved digital
technology
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FDMA
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Second Generation
Started in early 1990s, 2G uses digital transmissions
to transmits data between 9.5 Kbps and 14.4 Kbps
in 800 MHz and 1.9 GHz frequencies
Offers several advantages over analog, including
More efficient uses of frequency spectrum
Quality of voice transmission does not degrade
over distance
Better security; more difficult to decode
Requires less transmitter power
Uses smaller and less expensive individual
receivers and transmitters
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Second Generation
2G cellular networks use three different multiple
access technologies summarized in Table 8-2
Time Division Multiple Access (TDMA), shown in
Figure 8-6, allows 3 times as many calls over
a single channel as FDMA
Code Division Multiple Access (CDMA) allocates
entire spectrum all the time, as seen in Figure 8-7
Global Systems for Mobile Communications (GSM)
divides a 25 MHz channel into 124 frequencies,
each 200 KHz, and then uses 8 time slots to
transmit up to 9.6 Kbps
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TDMA
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CDMA
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2G Technologies
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2.5 Generation
2.5G is regarded as an interim generation
Sparsely deployed 2.5G networks operate at
384 Kbps
Packet-switched 2.5G networks have two
advantages over circuit switched networks
More efficient, increasing traffic from 3 to 5
times over that of circuit-switching
“Always on” with connection kept open all the
time
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2.5 Generation
2.5G networks use three technologies
General Packet Radio Service (GPRS) uses 8
time slots in a 200 KHz spectrum to transmit at
speeds up to 114 Kbps
Enhanced Data Rates for Global Evolution
(EDGE) uses new modulation technique to
transmit up to 384 Kbps
CDMA2000 1XRTT supports 144 Kbps packet
data transmissions
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Third Generation
3G is intended to be a uniform global
worldwide standard for cellular wireless
communication
International Telecommunications Union
(ITN) has outlined standard data rates for
wireless digital networks
144 Kbps for a mobile user
386 Kbps for slowly moving user
2 Mbps for stationary user
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Third Generation
Transition from CDMA2000 1XRTT is to
CDMA200 1XEVDO with data transmission rates
of 2.4 Mbps
Must be coupled with CDMA2000 1XRTT for
both voice and data transmissions
CDMA2000 1XEVDV will send both voice and
data
Transition from EDGE is Wideband CDMA
(WCDMA)
Adds packet-switching data channel to circuitswitched voice channel to transmit at 2 Mbps in
fixed position and at 300 Kbps when mobile
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Third Generation
Several 3G technologies not yet tested
Actual technologies may be different from
those currently proposed
Figure 8-8 shows digital wireless cellular
migration paths
Table 8-3 summarizes digital cellular
technologies
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Digital Wireless Cellular
Migration Path
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Digital Cellular
Technologies
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Client Software
Client software that functions on wireless
digital cellular devices provide function and
user interface to display or manipulate data
Some client software is unique to cellular
telephones
Other software may be used in a variety of
different applications
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Wireless Application
Protocol (WAP)
WAP provides standard way to transmit,
format, and display Internet data on cellular
phones
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Display only textual data because of slow
transmission speed and smaller viewing area, as
seen in Figure 8-9
Has a microbrowser that uses Wireless Markup
Language (WML) instead of HTML, as seen in
Figure 8-10
A WAP Gateway, also called a WAP Proxy,
changes HTML into WML before forwarding it to
cell phone, as seen in Figure 8-11
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WAP Display
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HTML Code
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WAP
8 HTML and WML Differences
HTML controls layout, color, font, and styling,
while WML controls only font size and basic
font attributes, as seen in Figure 8-12
WML uses Extensible Markup Language (XML)
and tags that specify how content should be
formatted
WML document, called a deck, contains one or
more blocks called cards that contain small parts
of a text document and navigation controls
One card is displayed on the cell phone at a time
as seen in Figure 8-13
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WML Code
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WML Deck
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i-Mode
i-Mode, a Japanese-owned Internet access
system, is based on compact HTML
(cHTML)
Has its own set of tags and attributes
Users are charged for the service by amount of
information downloaded plus a service charge
Expect i-Mode and WAP to merge into one
technology in the future
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Java
Developed by Sun Microsystems, Java is an
object-oriented language that runs on almost
any hardware platform
Java 2 Micro Edition (J2ME) was specifically
developed for programming wireless devices
Allows cellular phone to access remote
applications and email
Can also run programs on cellular phone itself
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Binary Runtime Environment
for Wireless (BREW)
BREW, a runtime environment, is a thin
software interface, that resides on wireless
device
Users can download programs and run them on
BREW-enabled devices
BREW uses memory efficiently, occupying
only a small amount of flash memory and
dynamically allocating RAM
Can be used in combination with other
operating systems and any kind of browser
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Limitations and the Future
WAP and i-Mode allow remote access to
the Internet
They do not support a rich set of graphics
J2ME and BREW are expected to become
major platforms for variety of wireless
devices
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Digital Cellular Issues and
Outlook
Several issues face digital cellular telephony
that prevent its rapid acceptance
Competing technologies—no single road to 3G
digital telephony; competing technologies are
incompatible
Limited spectrum availability—No part of
spectrum is designated exclusively for 3G; is
enough spectrum available to meet needs
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Digital Cellular Issues and
Outlook
Several issues face digital cellular telephony
that prevent its rapid acceptance
High infrastructure costs—3G telephones may
cost as much as $300 with $90 monthly charge;
carriers will spend billions for infrastructure
necessary for 3G
Competition from other wireless options—
Bluetooth, IrDA, and 802.11a WLANs are lessexpensive choices
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Chapter Summary
Two keys to cellular telephone networks are
dividing coverage area into cells and using
low power levels for transmission
At the center of each cell is a cell transmitter
that sends and receives radio frequency (RF)
signals
Low-power levels enable signals to stay
confined to the cell and not interfere with other
cells that use the same frequencies
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Chapter Summary
All cell phones have special codes that
identify the owner and carrier or service
providers
Handoff is when user moves to another cell
and is automatically associated with base
station of new cell
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Chapter Summary
Roaming occurs when a user moves beyond
coverage area of entire cellular network and
connects to network in remote area
Remote area network communicates with home
area to verify that user can make calls and is
charged appropriately
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Chapter Summary
First generation of wireless cellular
technology, known as 1G, uses analog
signals and transmits at a maximum speed
of 9.6 Kbps
1G uses Advanced Mobile Phone Service
(AMPS) standard
Operates in 800-900 MHz frequency
Uses Frequency Division Multiple Access
(FDMA)
Is circuit-switching technology
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Chapter Summary
Second generation, known as 2G, transmits
data between 9.6 Kbps and 14.4 Kbps in
800 MHz and 1.9 GHz frequencies
Circuit-switched digital technology
Use three different multiple access
technologies:
 Time Division Multiple Access (TDMA)
Code Division Multiple Access (CDMA)
Global Systems for Mobile (GSM)
communications
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Chapter Summary
Currently, three variations in 2.5G interim
generation of packet-switching network
technologies:
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General Packet Radio Service (GPRS) is for
TDMA or GSM 2G networks
Enhanced Data Rates for Global Evolution
(EDGE) is considered a “booster” for GPRS
systems and can transmit up to 384 Kbps using
a new modulation technique
CDMA2000 1XRTT supports 144 Kbps packet
data transmission and doubles voice capability
of current CDMA networks
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Chapter Summary
3G digital networks transmit at higher
speeds and provide new or expanded
applications and features
Will require major changes to network
infrastructures and a new generation of mobile
cellular devices
Widely used in Europe and Japan, Short
Message Services (SMS) allows delivery of
text-based messages directly between
wireless devices
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Chapter Summary
Client software on cell phone is necessary for
Internet surfing or videoconferencing
Wireless Application Protocol (WAP) provides
a standard way to transmit, format, and display
Internet data without requiring rich user interface
WAP cell phone runs microbrowser that uses
Wireless Markup Language (WML) to display textbased Web content
A WAP Gateway must translate between WML and
HTML
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Chapter Summary
I-mode, another client technology, is based
on compact HTML (cHTML)
It has its own set of tags and attributes
Expected I-mode and WAP to merge into
one technology in the future
Java 2 Micro Edition (J2ME) is a Java
subset for programming wireless devices
Allows cellular phones to access remote
applications and e-mail programs as well as
run programs
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Chapter Summary
Binary Runtime Environment for Wireless
(BREW), a thin software interface layer,
resides on a wireless device
Allows users to download programs and run
them on BREW-enabled devices
Competing cellular technologies, lack of
standards, spectrum limitations, and high
costs of implementing 3G technology have
prevented rapid acceptance of advanced
generations of digital cellular telephony
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Chapter Summary
3G networks have competition from other
wireless technologies
Top speed for 3G is 2 Mbps standing still,
but 802.11a WLANs offer speeds over 100
Mbps while mobile
Some carriers install less-expensive stable
WLANs in high-traffic “hot spots” in
selected cities as alternative to 3G
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