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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 functionsList and describe the features of the

generations of cellular telephonyList and describe the four types of client

software used on a digital cellular telephoneDiscuss 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 telephonyVariety 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 InternetSMS is popular in Europe and Japan with over

200 billion messages sent annuallySMS 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 networksCoverage 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 8-1All 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 8-3Network 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 generationsFirst GenerationSecond Generation2.5 GenerationThird 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

passband832 frequencies are available, with 790 used

for voice traffic and 42 for control channelThese 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 8-5User 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 technologyBecause analog signals are prone to interference,

1G is used basically for voiceIt 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, includingMore efficient uses of frequency spectrumQuality of voice transmission does not degrade

over distanceBetter security; more difficult to decodeRequires less transmitter powerUses 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 8-2Time 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 generationSparsely deployed 2.5G networks operate

at 384 KbpsPacket-switched 2.5G networks have two

advantages over circuit switched networksMore 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 technologiesGeneral 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 networks144 Kbps for a mobile user386 Kbps for slowly moving user2 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 MbpsMust be coupled with CDMA2000 1XRTT for

both voice and data transmissionsCDMA2000 1XEVDV will send both voice and

dataTransition from EDGE is Wideband CDMA

(WCDMA) Adds packet-switching data channel to circuit-

switched 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 testedActual 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 phonesDisplay 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

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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 8-12WML 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 attributesUsers 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 devicesAllows 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 deviceUsers can download programs and run them on

BREW-enabled devicesBREW 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 InternetThey 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 acceptanceCompeting 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 acceptanceHigh 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 less-expensive 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 transmissionAt 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 areaRemote 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 frequencyUses 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 frequenciesCircuit-switched digital technologyUse 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:General Packet Radio Service (GPRS) is for TDMA

or GSM 2G networksEnhanced 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 featuresWill 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 interfaceWAP cell phone runs microbrowser that uses

Wireless Markup Language (WML) to display text-based 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 devicesAllows 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 deviceAllows users to download programs and run

them on BREW-enabled devicesCompeting 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