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おける送信電力制御法の研究

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System

Yasuo Koide

Scho ol of Information Science,

Japan Advanced Institute of Science and Technology

February 15, 2001

Keywords: CDMA, PowerControl,Mobile Communication, Multimedia

Communication.

Abstract

A shortage of channelresources inmobile communication, especiallyin cellular

phonesystem,isaseriousproblem,whichiscausedbyrapidincreaseofmobilephone

users. And multimedia communication service of high rate and high quality data

transferforconnectingInternetandrealtimevideotelephonywillbeprovidedinthe

third generation mobile communication system. However transmiting bandwidth

can not be expanded freely as it is limited in radio enviroments. Therefore it is

necessarytoimprove spectraleciency.

Thispaperprop osesanewp owercontrolmetho dformultimediatracinCDMA

cellularphonesystem. MultimediaTrachasvarietyofrequirementsoncommuni-

cationrateand qualityforeach trac. The proposed systemsetan optimaltarget

receiving powerto it according to the required transfer rate and quality. The re-

sultsofproposed systemshowsthatnumb erofuserscanincrease,keeping required

quality.

1 Introduction

DS-CDMA system has characteristics that spectral eciencyis highest incellularphone

systems and it suits for multimedia communication, because transmission rate can be

changed easily by varying spread rate(spread-spectrum processing gain). In the third

generationmobilecommunication,highspeed datacommunication,outdoor384kbpsand

indoor 2Mbps, is planed and its application is high rate and high quality data transfer

such as music, a picture, movie and realtime video telephony. However a shortage of

Copyright c

2001byYasuoKoide

is limited.

A new power control method for multimedia trac in CDMA cellular phone system

is proposed. The objective is improvement of spectral eciency. The author directs his

attention to variety of trac characteristic in required communication rate and quality.

As aresult, it ispossible toincreasethe numb er ofusers inthe system.

2 Cellular Phone System

In cellular phone system, many BTSs havingsmall area are allo cated in service area. A

Channel can bereuse eciency insame system and itincrease channel resource.

CDMA system was adopted air interfece between BTS and MS of next generation

mobilecommunication,becauseitis highsp ectraleciency andsuit multimediacommu-

nication.

3 DS-CDMA System

In CDMA system, information bit is spreaded directly using spreading code with short

period intransmitter and respreaded it using same codein areciver. The originalsignal

is restore in the result. Channel separation is possible in same frequency band when

spreading co de with eachchannelhave highauto-correlation and lowcross-correlation.

4 Conventional Power Control

Distance between BTS and each MS isvery dierent. If all MSstransmit asingnal with

same power, received power at BTS with the radius of 10km is dierent a million time

when a signal is attenuated square of distance. This dierence of recived power very

aect correlation of co de and it can't decode correct information bit. Therefore we have

to control transmit powerin orderto receiveat same poweratBTS.

5 New Power Control for Multimedia Trac

Requied communicationrate and quality isdierent witheach tracin multimedia. We

propose new power control for multimedia trac. In new system, target recived power

at reciver is changed by spreding rate and quality, it adjust correlation of code to the

optimumcondition. Keeping requiredquality,itisp ossibletoincreaseuserinthesystem.

Simultaneously,target reciving powerisperformedthe minimum requirementsp owerfor

reduce interferenceto neighb or cell and consumption powerata mobile unit.

Noiseisaddedaninformationsignalbyairpropagationandthermalnoiseofatransmitter

anda receiver. Interferenceofchannelmultiplexaect channelquality inCDMAsystem.

Accordingly we examineabout inuence of these inmultimediatrac.

7 Verication of New Power Control Performance

WeverifyPerformanceofproposednew p owercontrol formultimediatrac bycomputer

simulation. Weveriedusersisincreasecomparedwithusingconventionalpowercontorol.

we showa rate of users increasewith each mixing rate ofmedia typ e and verifyfunction

of addmission contorol and algorithm of decreasein targetreciving power.

8 Consideration

Wecosidered ab out aresult ofcomputer simulation. Andwecompareda numb erof user

using prop osed algorithm with real maximum users. As aresult, it ismuchthe same.

9 Result

We proposed new power control for multimedia trac in CDMA system, for improving

spectrum eciency, and showed its algorithm. Its p erformance is veried by computer

simulation. Users are increased compared with conventional powercontorol.