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

Abstract

The asymptotic performance of Reed-Solomon (RS)coded M-ary orthogonal signaling with ratio-threshold test (RTT) type demodulation in a Rayleigh-fading channel is considered. We show that the minimum (E) over bar(b)/N-o needed for error-free communication is e ln2 (2.75 dB) with RTT, and 4.79 (6.8 dB) with hard decisions. The optimum code rate that minimizes the required (E) over bar(b)/N-o is c(-1) with RTT and 0.46 with hard decision, and the optimum ratio threshold approaches 1 for large M. Nest, ne 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 x M Hadamard matrix with a user-specific random sequence of length N. We derive the minimum (E) over bar(b)/N-o for error-free communication as a function of the number of users, the optimum code rate that minimizes (E) over bar(b)/N-o, end 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 (E) over bar(b)/N-o and the optimum code rate for each traffic type.