Performance limits of Reed-Solomon coded CDMA with orthogonal signaling in a Rayleigh-fading channel

The asymptotic performance of Reed–Solomon (RS)codedM -ary orthogonal signaling with ratio-threshold test (RTT) type demodulation in a Rayleigh-fading channel is considered. We show that the minimum Eb=N0 needed for error-free communication is e ln 2 (2.75 dB) with RTT, and 4.79 (6.8 dB) with hard decisions. The optimum code rate that minimizes the required Eb=N0 is e 1 with RTT and 0.46 with hard decision, and the optimum ratio threshold approaches 1 for large M . Next, we investigate the fundamental limit in direct-sequence spread-spectrum multiple-access (DS/SSMA) system employing an M -ary orthogonal code of length N =Mm, which is obtained by spreading every row of an M M Hadamard matrix with a user-specific random sequence of length N . We derive the minimum Eb=N0 for error-free communication as a function of the number of users, the optimum code rate that minimizes Eb=N0, and the maximum limit on the total information transmission rate. Then, we consider a multirate DS/SSMA system, where a population of users simultaneously transmit at different power levels a variety of traffic types of different information rates. We derive the minimum required Eb=N0 and the optimum code rate for each traffic type.