On stability of DS-CDMA data networks employing retransmissions with memory

We study a DS-CDMA data network consisting of a single radio access point and a collection of M wireless terminals. The terminals generate bursty non-real-time packet streams, and transmit over a common broadband communication channel to the access point using different spreading codes. The spreading codes have non-zero cross correlations, and thus the terminals are mutually interfering. This interference gives rise to bistability, which can severely degrade throughput performance. We are interested in characterizing schemes that eliminate or at least significantly mitigate bistability. We focus on diversity combining via retransmissions with memory (RWM). RWM is related, at some level, to spreading gain control, but requires no closed-loop control. We show that under RWM, the system may possess multiple equilibria for a given arrival rate. However, the stable equilibrium points, and corresponding throughputs, are typically very close together. Thus RWM achieves high throughput, even if multiple equilibria exist