Dynamic performance of a random access code combining CDMA system

Previously (1994) the authors have analyzed the steady state performance of a random access code combining CDMA system. In this paper, the analysis is extended to the dynamic performance. We follow an approach similar to that used by Raychaudhuri (1981). The system is represented as a discrete-time Markov chain with the state being the number of backlogged terminals. At the start of a given time slot, each backlogged user k is characterized by P_k(L) (the probability that user k transmits successfully a data packet formed by the combination of L previously transmitted copies). Unlike Raychaudhuri´s system where the error rate on the channel is viewed by all transmitting users as the same constant during each time slot, P_k(L) varies from one user to another. Its value is substantially increased through the code combining operation (increases with L). As a result, the number of retransmissions is minimized. The throughput and time-delay performance are significantly improved. We show through numerical analysis that the code combining system performs better than the conventional one. The effect of code combining on the stability is also investigated