Performance Analysis of Forward Link DS-CDMA Systems Using Random and Orthogonal Spreading Sequences

Ji-Woong CHOI  Yong-Hwan LEE  

IEICE TRANSACTIONS on Communications   Vol.E87-B   No.8   pp.2195-2202
Publication Date: 2004/08/01
Online ISSN: 
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technology
forward link DS-CDMA,  orthogonal spreading sequence,  random spreading sequence,  

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The characteristics of the spreading sequence significantly affect the signal-to-interference power ratio (SIR) of the received signal in direct sequence code division multiple access (DS-CDMA) system. In this paper, we analyze the receiver performance of the forward link of a DS-CDMA system in terms of the SIR and bit error rate (BER) when pseudo noise (PN) codes and concatenated orthogonal/PN (OPN) codes are used as the spreading sequence. The use of OPN spreading codes can cancel out the intra-cell interference signals with equal path delay, but the use of PN spreading codes cannot, significantly degrading the performance. As a result, the BER performance of the OPN spreading system is better than that of the PN spreading system. The use of OPN spreading sequences can provide the system capacity at least two times larger than the use of PN spreading sequences in the single-cell environment even when the channel has a large number of multipaths. The two spreading systems also show significant difference in the user capacity even in a multi-cell environment.