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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