WCDMA Introduction Code Division Multiple Access

Chia-Chi Yu

2004.7.23

Outline

HistoryMultiple Access TechniqueWhy CDMA?Spread SpectrumHow CDMA work? (simulation)Problems in a CDMA system (simulation)

History

1949 C. Shannon develop basic ideas of CDMA 1991 First GSM network 1991 Development of IMT2000 and UMTS standards 1995 Commercial operation of CDMA system (IS-95)

in Hong Kong/Korea 1998 The first meetings of the 3GPP

release 4 5 6 7….

2005 UMTS service will be world wide (?)

Introduction

Wireless communication is the way of the futureApplications

Mobile phones Wireless LAN Global positioning system

Need Multiple Access!

Multiple Access Techniques

TDMATime Division Multiple Access

FDMAFrequency Division Multiple Access

CDMACode Division Multiple Access

SDMA Space Division Multiple Access

Why CDMA ?

Frequency limitedBandwidth Efficiency

Voice Activity ~40%

Variable Spreading Factor

Spread Spectrum

FHSSFrequency Hopping Spread Spectrum

THSSTrequency Hopping Spread Spectrum

DSSSDirect Sequence Spread Spectrum

DSSS

Data is spread by multiplying a high rate spreading code Receiver is de-spread by using the same code

Spectrum

Spectrum

Problems in a CDMA Channel

Near-Far Problem

CDMA system needs Power Control

Reference

http://www.umtsworld.com http://www.3gpp.org K. Riyyol,S-72.238 WCDMA system Qualcomm, Fundamentals of Wireless Communi

cations & CDMA A. J. Viterbi,Ed.,CDMA. Addison-Wesley 1995 S. G. Glisic Ed.,Adipative WCDMA. Wiley 2002