Error performance for diversity DS-SSMA communications in fading channels

Abstract

The average error probability for asynchronous direct sequence spread spectrum multiple access communications through slow Rician or Nakagami fading channels is evaluated for non-diversity and diversity receptions. The moments of the self-interference and the multiple access interferences are used to evaluate the average error probability by the Gauss quadrature rule. Diversity techniques and error correcting codes are used. Comparisons between the uncoded non-diversity DS-SSMA system and the coded diversity system are shown for a Gold code of codelength 127. Diversity and coding can improve the performance significantly. Using fourth order diversity and Reed-Solomon coding, the maximum achievable number of users is 12 percent of the code length for Rayleigh fading, when the average error probability is 10-3. Performance comparisons for Rician and Nakagami fading channels are also made. As the system is interference-limited, the performance seems to show no significant difference for the two fading channels when the number of users is large.