Performance analysis of a random access CDMA system with multiuser detection

In this paper, we approach the centralized multiuser detection problem by combining random access techniques and multiuser detection to provide a high-performance and low-complexity system. Users compete for N₁ time or frequency orthogonal channels. In each channel a DS-CDMA signaling format is employed. Since the average number of users per channel is much less than the total number of users, optimum multiuser detector can be practically used in each channel. The multiuser detector implemented at the receiver has a constraint on the maximum number of users per channel that it can handle. Uncaptured or exceeding transmissions have to be retransmitted according to the access protocol. Error probability and throughput analysis of the proposed system are presented and numerical results show that our system can achieve great performance advantage compared to a conventional detection DS-CDMA system with the same total processing gain