digital cellular telephony
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Digital Cellular Telephony. Chapter 8. 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 - PowerPoint PPT PresentationTRANSCRIPT
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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