Suppression effects of multiple access interference in DS/CDMA with code-diversity

This paper proposes a novel DS/CDMA system with code-diversity techniques c onstituted by a simple system to suppress multiple access interference (MAI ) without estimating the PN sequence of interference at the receiver. In th e transmitter, the data signal is modulated with a sum of several PN sequen ces, and, two types of code- diversity reception are proposed, (1) maximal- ratio combining (MRC) code-diversity by autocorrelation, and (2) MRC code-d iversity by anti-crosscorrelation. By computer simulations, it is shown tha t MRC code-diversity by anti-crosscorrelation is superior to the other one. It is also shown that MRC code-diversity by anti-crosscorrelation can impr ove BER more effectively for the interference which takes the phase to degr ade BER at the worst. Next, to design the optimum number of branches for co de-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. Fin ally, the effectivity of the proposed system in a near-far problem is prese nted.