Suppression Effects of Multiple Access Interference in DS/CDMA with Code-Diversity

Tetsuya SEKI  Masanori HAMAMURA  Shin'ichi TACHIKAWA  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E82-A    No.12    pp.2720-2727
Publication Date: 1999/12/25
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Spread Spectrum Techniques and Applications)
code-diversity,  DS/CDMA,  near-far problem,  multiple access interference,  maximal ratio combining,  

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This paper proposes a novel DS/CDMA system with code-diversity techniques constituted by a simple system to suppress multiple access interference (MAI) without estimating the PN sequence of interference at the receiver. In the transmitter, the data signal is modulated with a sum of several PN sequences, and, two types of code- diversity reception are proposed, (1) maximal-ratio combining (MRC) code-diversity by autocorrelation, and (2) MRC code-diversity by anti-crosscorrelation. By computer simulations, it is shown that MRC code-diversity by anti-crosscorrelation is superior to the other one. It is also shown that MRC code-diversity by anti-crosscorrelation can improve BER more effectively for the interference which takes the phase to degrade BER at the worst. Next, to design the optimum number of branches for code-diversity, average BERs are calculated for several combinations of codes in code-diversity. As a result, the optimum number of branches varies for each combination of codes, however, it is decided from 3 to 7 branches. Finally, the effectivity of the proposed system in a near-far problem is presented.