ERROR PERFORMANCE FOR DIVERSITY DS-SSMA COMMUNICATIONS IN FADING CHANNELS

The average error probability for asynchronous direct sequence spread spectrum multiple access communications through slow Rician or Nakagam i fading channels is evaluated for nondiversity and diversity receptio ns. The moments of the self-interference and the multiple access inter ferences are used to evaluate the average error probability by the Gau ss quadrature rule. Diversity techniques and error correcting codes ar e used. Comparisons between the uncoded nondiversity DS-SSMA system an d the coded diversity system are shown for a Gold code of codelength 1 27. Diversity and coding can improve the performance significantly. Us ing fourth order diversity and Reed-Solomon coding, the maximum achiev able number of users is 12 percent of the code length for Rayleigh fad ing, when the average error probability is 10(-3). Performance compari sons for Rician and Nakagami fading channels are also made. As the sys tem is interference-limited, the performance seems to show no signific ant difference for the two fading channels when the number of users is large.