SELECTION DIVERSITY FOR DS-SSMA COMMUNICATIONS ON NAKAGAMI FADING CHANNELS

Average error probability and outage probability for asynchronous bina ry direct sequence spread-spectrum multiple access communications thro ugh slow nonselective Nakagami fading channels are evaluated for nondi versity and diversity receptions. Using a Gauss quadrature rule, the m oments of the multipath interference and multiple access interferences are used to evaluate the conditional probability conditioned on a fix ed fading amplitude of the desired signal. Average error probability w hich is the expected value of the conditional probability is evaluated by trapezoidal integration. The pdf of the desired signal is Nakagami m-distributed for nondiversity reception. For diversity reception, th e pdf of the desired signal is evaluated for selection diversity. Comb ining the diversity technique and Reed-Solomon codes, comparisons betw een the uncoded nondiversity DS-SSMA system and that of the coded dive rsity system are shown for a Gold code of codelength 127. Using fourth -order diversity and Reed-Solomon coding, the maximum achievable numbe r of users is 12% of the codelength for Rayleigh fading, when the aver age error probability is 10(-3). The corresponding outage probability is less than 5%.