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Mobile COMMUNICATION

INTRODUCTION

LECTURE 1

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Wired Vs. Wireless

Communication

Wired WirelessEach cable is a different channel One media (cable) shared by all

Signal attenuation is low Highsignal attenuation

No interference High interference

noise; co-channel interference; adjacent

channel interference

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Why go Wireless?Advantages Sometimes it is impractical to lay cables

User mobility Cost

Limitations

Restricted frequency range Standards are often restricted Security

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Objectives of Wireless

Systems Large Capacity

Efficient use of Resources (Spectrum)

Adaptability to traffic density

Quality of Service

Affordability

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Mobile Radio Communication

Systems Garage door openers Remote controllers

Cordless phones Hand held walkie-talkie Pagers Cell telephones

These systems differ in cost, complexity,performance and application.

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Definitions MOBILE

Broadly, it is a radio terminal that can be movedduring operation.

Difference between MOBILE & PORTABLE

MOBILE: a radio terminal attached to a high speedmobile platform. (Cell phone in a fast moving vehicle)

PORTABLE: a hand-held radio terminal that can beused by someone at walking speed. (Walkie-talkie orcordless phone inside a home)

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Classification of Mobile Radio

Communication Systems Simplex Systems

Half Duplex Systems

Full Duplex Systems

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Classification of Mobile Radio

Communication Systems Simplex Systems: Only one way

communication possible. Messages can bereceived but not acknowledged. (paging

systems)

Half-Duplex Systems: 2 waycommunication possible but the same radio

channel used for both transmission andreception. At any given time a user can onlytransmit or only receive information; Push totalk and release to listen systems.

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Classification of Mobile Radio

Communication Systems Full-Duplex Systems:Allow simultaneous

transmission and reception b/w subscriber

and Base Station

Simultaneous transmission and receptionachieved by:

Frequency Division Duplex (FDD)

Time Division Duplex (TDD)

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Simplex Connection:transmit orreceive

Duplex Connection:simultaneous

transmission and reception

Over

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Frequency Division Duplex

(FDD) Uses a pair of frequency bands one for

Forward Channel and another for ReverseChannel

Forward Channel: used for transmission ofinformation from Base Station to Mobile

Reverse Channel: used for transmission ofinformation from Mobile to Base Station

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Frequency Division Duplex

(FDD) FDD provides simultaneous radio transmission

channels for subscriber and Base Station so

that they both may constantly transmit whilesimultaneously receiving signals from oneanother

used in analog mobile radio systems

requires good frequency separation filters

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Simplex Systems Example:

Paging Systems Used to send a brief message or page

to subscriber ( numeric, alphanumeric,

voice message)

Typically used to notify a subscriber of

the need to call a specific phonenumber or travel to a particular locationto receive further instructions

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Paging Systems A page is sent to a paging subscriber via

paging system access number

The paging system transmits the pagethroughout the service area using basestations which broadcast the page on a radiocarrier

Paging systems vary in their complexity andcoverage area

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Paging Systems

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Full-Duplex Systems Example:Cordless Telephone Systems

Wireless connection between a portablehandset and a dedicated Base Station

which is then connected to a dedicatedtelephone line with a specific telephonenumber on a Public Switched Telephone

Network (PSTN)

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Cordless Telephone Systems

PSTN Fixed Port(BaseStation)

CordlessHandset

Wireless Link

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Cellular Telephone Systems

developed by Bell Labs 1960s-70s It is the subdivision of a relatively large coverage zone into

small cells, each of which reuses portions of the spectrum toincrease spectrum usage

a system approach, no major technological changes few hundred meters in some cities, 10 km at countryside each served by base station with lower power transmitter Each base station is allocated a portion of the total channels

available to the system neighboring cells assigned different groups of channels, interference minimized

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Cellular Concept

Cellular telephone systems replaced mobile systemsserving large areas operating with a single basestation and a single high-power transmitter withmany smaller areas (cells), each with its own basestation and low-power transmitter.

With the cellular concept, each area is further dividedinto hexagonal-shaped cells that fit together to forma honeycomb pattern. The hexagon shape waschosen because it provides the most effectivetransmission by approximating a circular patternwhile eliminating gaps inherently present betweenadjacent circles.

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Quantum Leap in Mobile Communications:

Single Cell Systems Cellular Systems

radius

r

re-use distance

r

Single Cell

System

Cellular

System

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Frequency ReuseThe process in which the same set of frequencies (channels) can be

allocated to more than one cell, provided cells are separated by sufficientdistance

The idea springsfrom the FCCallocation ofspecific channelsfor radio or TVstations in oneregion of thecountry and thenthe reallocation ofexactly the samechannels todifferent stationsin completelydifferent part ofthe country

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Cellular Telephone Systems

Provide wireless connection to PSTN forany user within range of system

Accommodate large number of usersover a large geographical area, withinlimited frequency spectrum

Provide high quality service comparableto landline telephone systems

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Basic Cellular SystemComponents

Mobile Stations (MS)

Base Stations (BS)

Mobile Switching Centre (MSC)

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Basic Cellular SystemComponents

Mobile stations constitute a transceiver, antenna andcontrol circuitry maybe mounted in a vehicle or usedas a hand held unit.

Base stations generally constitute towers supportingseveral transmitting and receiving antennas BS handles full duplex communication

Serves a bridge between mobile users in a cell and MSC

MSC coordinates activities of all BSs and connects allmobiles in a cellular system to PSTN

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Cellular Network Architecture

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Base Station-MobileNetwork

Controlchannelsused fortransmissionof callsetup, callrequest, callinitiation

and othercontrolsignals

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Brief Outline of CellularProcess

Telephone call placed to mobile user

Telephone call made by mobile user

When a cell phone is turned on, it first scans the group of FCCto determine the one with the strongest BS signal.

That CC is monitored until the signal drops below a usable valueupon which the cell phone again scans the CCs in search of thestrongest signal.

CCs are defined and standardized over the entire geographicarea covered and constitute about 5% of the total channelsavailable in the system. Rest 95% is dedicated to voice and datatraffic.

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Telephone Call to Mobile User

Step 1 The incoming telephone call to Mobile X isreceived at MSC.

Step 2 MSC dispatches the requested MobileIdentification Number (MIN) i.e. telephone number ofMobile X, to all base stations (BSs) in the cellularsystem.

Step 3 The BSs broadcast the MIN as a pagingmessage over the FCC throughout the cellularsystem.

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Telephone Call to Mobile User

Step 4 The mobile receives the paging messagesent by the BS it monitors and responds byidentifying itself over the reverse control channel

Step 5 The base station relays theacknowledgement sent by the mobile and informsMSC of the handshake

Step 6 The MSC instructs the base station to movethe call to an unused voice channel pair within thecell

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Telephone Call to Mobile User

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Handover

When a mobile moves into a differentcell while a conversation is in progress,

the MSC automatically transfers the callto a new channel belonging to the newbase station

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Telephone Call placed byMobile User

Step 1 When a mobile originates a call, acall initiation request is sent on the RCC along

with its own phone number (MIN), electronicserial number (ESN) and phone number ofcalled party.

Step 2 The cell base station receives thedata and sends it to the MSC.

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Telephone Call placed byMobile User

Step 3 MSC validates the request,makes connection to the called party

through PSTN and instructs the BS andmobile to move to an unused FV andRV channel pair to allow conversation to

begin.

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Telephone Call placed byMobile User

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Call initiated by a mobile isestablished

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Comparison of Mobile CommunicationSystems- Base Station

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EVOLUTION OF WIRELESSCOMMUNICATION

The wireless landscape is characterizedby continual evolution, rapid innovation

and technological change Researches are persistently

investigating techniques that make

efficient use of available spectrum andoffer consumers greater range, qualityof service, and data transfer rates

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Advanced Mobile PhoneService (AMPS)

First-generation cellular took off in 1982 with thedeployment of commercial AMPS in U.S.

Originally, AMPS operated in the 800 MHz frequency

band FDMA employed Channel bandwidth: 30kHz Uplink Frequency Range: 824-849 MHz Downlink Frequency Range:869-894 MHz The band accommodated 832 duplex channels

among which 21 were reserved for call setup and therest for voice communication

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Advanced Mobile PhoneService (AMPS)

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Total Access CommunicationSystem (TACS)

TACS is the European version of AMPS

After its introduction in U.K. in 1985,

over 25 countries offered TACS services

Channel Bandwidth:25 kHz each

Uplink Frequency Range: 890-915 MHz Downlink Frequency Range: 935-960

MHz

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TACS

Extended TACS (ETACS) An additional 16 MHz of channel bandwidth was added to

accommodate more channels to form ETACS

JTACS Japanese version of TACS

The only significant differences were the frequency bandsand number of channels

Narrowband TACS (NTACS) Another variation of TACS which reduced channel bandwidth

from 25 kHz to 12.5 kHz.

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Nordic Mobile Telephone(NMT)

NMT system was developed by thetelecommunications administrations ofSweden, Norway, Finland, and Denmark to

create a compatible mobile telephone systemin the Nordic countries

The first commercial NMT 450 cellular

system was available at the end of 1981 Due to its rapid success and limited capacity

of the original system design, NMT 900system version was introduced in 1986

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NMT

NMT 450 used a lower frequency (450 MHz)and higher maximum transmitter power level

which allowed a larger cell site coverageareas

NMT 900 used a higher frequency(approximately 900 MHz band) and a lower

maximum transmitter power which increasedsystem capacity

NMT 450 and 900 could co-exist

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NMT

When NMT mobile phones accessed the cellularsystem, they either found an unused voice channeland negotiated access directly or began conversationwithout the assistance of a dedicated control channel

Since scanning for free voice channels is very timeconsuming, NMT 900 used a dedicated controlchannel called the calling channel

NMT 450 was frequency duplex with 180 channels(except Finland which only had 160 channels)

Channel Bandwidth=25 kHz with a frequency duplexspacing of 10 MHz

NMT 900 system had 999 channels

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Problems with 1G

Numerous incompatible 1G services emergedaround the world during 1980s

each carrier delivered service to a limitedserving area

there were no standards to enable roaming

channel capacity was rapidly beingexhausted.

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Gl b l S t f M bil

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Global System for MobileCommunication (GSM)

Initially created to provide a single standard pan-European cellular system

Uses TDMA technology

Its development began in 1982, and the firstcommercial GSM digital cellular system was activatedin 1991

GSM has evolved to be used in a variety of systemsand frequencies (900 MHz, 1800 MHz and 1900 MHz)including Personal Communications Services (PCS) inthe U.S. and Personal Communications Network(PCN) systems throughout the world

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IS-136 TDMA

Uses TDMA technology

Evolved from the IS-54 specification

that was developed in U.S. in the late1980s to allow the gradual evolution of

AMPS to digital service

Also referred to as Digital AMPS(DAMPS) or North American DigitalCellular (NADC)

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IS-136 TDMA

Primary Features:

Ease of adaptation to the existing AMPS This is due to the fact that IS- 136 radio channels retain the

same 30 kHz bandwidth as AMPS channels The development of dual mode mobile telephones

operating on either IS-136 digital traffic (voice anddata) channels or the existing AMPS radio channels

All IS-136 TDMA digital radio channels are dividedinto frames with 3 time slots

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Extended TDMA (E-TDMA)

Developed by Hughes Network Systems in 1990 as an extensionof IS-136 TDMA

ETDMA uses the existing TDMA radio channel bandwidth andchannel structure and its receivers are tri-mode as they can

operate in AMPS, TDMA, or ETDMA modes

Difference b/w TDMA & E-TDMA

TDMA assigns a time slot to a specific conversation whether

or not anyone is speaking at that moment, which wastesBandwidth

ETDMA assigns subscribers dynamically on requirementbasis

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E-TDMA

When subscribers have something totransmit, they put one bit in the bufferqueue.

System scans the buffer, notices that the userhas something to transmit, and allocatesbandwidth accordingly

If a subscriber has nothing to transmit, the

queue simply goes to the next subscriber. So, instead of being arbitrarily assigned, time

is allocated according to need

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IS-95 CDMA

Allows for voice or data communications on either a 30 kHzAMPS channel (when used on the 800 MHz cellular band) or anew 1.25 MHz CDMA channel

CDMA channels are unique in the sense that CDMA multiplies

(and therefore spreads the bandwidth of) each signal with aunique Pseudo-random Noise (PN) code that identifies each userwithin a channel and is independent of the data of that user.

Each CDMA channel contains the signals of many ongoing calls(voice channels) together with pilot, synchronization, paging,and control channels

Receivers select the signal they are receiving by correlating(matching) the received signal with the proper PN sequence.

The use of unique codes allows multiple users to access thesame frequency band simultaneously thus rendering CDMA ashighly spectrally efficient.

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IS-95 CDMA

Each IS-95 CDMA channel is divided into 64 separate (PNcoded) channels

A few of these channels are used for control, and the remainingcarry voice information and data

Original IS-95 throughput rate for a dedicated user specified as9.6 kbps Later on this rate was improved to 14.4 kbps for IS-95A In IS-95B each user can be assigned up to 8 traffic channels

simultaneously for a data throughput of 115.2 kbps per user In 1997 the CDMA Development Group (CDG) registered the

trademarkcdmaOne TM as a label to identify 2G systems basedon the IS-95 standard and related technologies

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2.5 G

Key Features:

Use digital packet switching technology,

providing increased capacity on the 2G radiochannels and higher throughput (up to 384kbps) for data service

The data channels are optimized for packet

data, which introduces access to the internetfrom mobile devices, streaming video andenhanced multimedia applications

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GPRS

GPRS allows packet radio service on theGSM system

Adds (defines) new packet channelsand switching nodes within the GSMsystem

Provides for theoretical datatransmission rates up to 172 Kbps

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EDGE

An evolved version of GSM

Uses 8 levels Phase Shift Keying (8PSK)

and packet transmission for advancedhigh-speed data services

Provides for theoretical data

transmission rates up to 547.2 Kbps

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Third Generation (3G)

The International Telecommunications Union (ITU)made an effort to establish a single standard forwireless networks in 1999 to standardize wireless

communications and make global roaming with asingle handset possible

The concept of a single standard evolved into afamily of 3G wireless standards of which the mostwidely accepted are: CDMA2000 Wide-band CDMA (WCDMA)

Time Division Synchronous CDMA (TD-SCDMA).

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Various upgrade paths for

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Various upgrade paths for2G technologies

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3G CDMA2000TM

CDMA2000 is a family of standards evolved from IS- 95 CDMA Offers enhanced packet transmission protocols for advanced

high-speed data services Retains original 2G CDMA bandwidth of 1.25 MHz per radio

channel Maintains backward compatibility with IS-95A(cdmaOne) and

IS-95B subscriber equipment Allows CDMA operators to introduce 3G capabilities at each cell

w/o changing entire base stations or reallocating spectrum Overseen by the Third Generation Partnership Project 2

(3GPP2), a standards setting project focused on developingglobal specifications for 3G systems

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3G CDMA2000TM

cdma2000 1xRTT First 3G CDMA air interface Employs a single 1.25 MHz radio channel

1XRTT implies one times the original cdmaOne bandwidth RTT= Radio Transmission Technology

Supports instantaneous data rates upto 307 kbps for a user in packet mode Yields throughput rates of upto 144 kbps per user depending on

No of users Velocity of a user and Propagation conditions

Can support twice as many voice users as the 2G CDMA standard Gives subscriber unit upto 2xtimes standby time for longer battery life

Only new backbone software and new channel cards at base station required toimplement cdma2000 1xRTT Being developed for both wide area mobile cellular coverage (FDD) as well as

indoor cordless type application (TDD)

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3G CDMA2000TM

Cdma2000 1xEV An evolutionary advancement for CDMA HDR packet standard overlaid upon existing IS-95, IS-95B and cdma2000

networks Later modified by Qualcomm for compatibility with W-CDMA

Gives CDMA carriers the option to install radio channels with dataonly=cdma2000 1xEV-DO or With data and voice=cdma2000 1xEV-DV With cdma2000 1xEV, individual 1.25 MHz channels can be installed in CDMA

base stations for specific high speed packet data access with in selected cells Cdma2000 1xEV-DO dedicates radio channel to data users only and supports

greater than 2.4 Mbps of high speed packet throughput per user on a particularCDMA channel

Actual data rates much lower i.e. in range of several hundred kbps Cdma2000 1xEV-DV offers usable data rates upto 144 kbps with twice as many

voice channels as IS-95B

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3G CDMA2000TM

cdma2000 3xRTT Ultimate 3G solution for CDMA Uses three adjacent 1.25 MHz radio channels to provide packet data

throughput speeds in excess of 2 Mbps per user Two possible ways of implementing cdma2000 3xRTT

3 non adjacent channels op simultaneously and in parallel as individual 1.25MHz channel (no new RF hardware req at BS) or

Adjacent channels combined into a single 3.75 MHz super channel (new RFhardware at BSma)

Cdma2000 standards claim a more seamless and less expensivemigration to 3G services when compared to W-CDMA as cdma2000allows at each BS the use of same Spectrum Bandwidth RF equipment Air interface framework

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3G WCDMA (UMTS)

Backward compatibility with 2/2.5G GSM, IS-136 & PDC TDMAtechnologies

Network structure and bit level packaging of GSM data retainedby W-CDMA with additional capacity given by new CDMA airinterface

Uses radio channels that have a wider bandwidth than 2Gsystems such as GSM or IS-95 CDMA

WCDMA deployed in a 5 MHz channel plan which requirecomplete replacement of RF equipment at each BS

Each W-CDMA 5 MHz radio channel able to support b/w 100 &

350 simultaneous voice calls at once depending on User velocity Propagation condition and Ae techniques such as sectoring an polarization

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3G WCDMA (UMTS)

Air interface standard designed for always on packet basedwireless services

Enables computers, entertainment devices and telephones toshare one wireless network and be connected to Internetanywhere, anytime

Supports packet data rates upto 2.048 Mbps for a stationeryuser

Provides high quality data, multi media, streaming audio/videoand broadcast services

Future versions of W-CDMA promise a stationary user data rates

in excess of 8 Mbps Being developed for both wide area mobile cellular coverage

(FDD) as well as indoor cordless type application (TDD)

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TD-SCDMA

A Chinese standard offering voiceservices and data services, both circuit-

switched and packet-switched Relies on existing core GSM infra

structure

Uses Time Division Duplex (TDD)

Upto 384 kbps of packet data providedto data user in TD-SCDMA

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4G

This can only be achieved by the convergence ofwired and wireless technologies

4G systems are expected to solve the still remaining

problems of 3G systems and to provide a widevariety of new services, from high quality voice tohigh definition video to high data rate wirelesschannels

MAGICMobile multimedia,Anytime anywhere,

Global mobility support, Integrated wireless solution,and Customized personal service.

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4G

4G systems are intended to complement and replace 3G systems,perhaps in 5 to 10 years

They will have: Broader Bandwidth higher data rate seamless Integration of terminals, networks, and applications to satisfy

increasing user demands

The all-encompassing integrated perspective shows the broad range ofsystems that 4G intends to absorb including: satellite broadband cellular 3G systems Wireless Local Loop (WLL) Fixed Wireless Access (FWA) Wireless Local Area Network (WLAN) Personal Area Network (PAN)

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4G

Many companies have taken self-serving definitions of 4G tosuggest they have 4G already in existence today, such asseveral early trials and launches of WiMAX (WorldwideInteroperability for Microwave Access Inc.) (group promotingIEEE 802.16 wireless broadband standard) which is part of the

formal ITU standard for 3G Other companies have made prototype systems calling those 4G

While it is possible that some currently demonstratedtechnologies may become part of 4G, until its standard orstandards have been defined, it is impossible for any companycurrently to provide with any certainty wireless solutions thatcould be called 4G cellular networks conforming to the eventualinternational standards for 4G.

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4G