A QoS framework for stabilized collision channels with multiuser detection

Recent work has shown that cross-layer optimization of the physical layer and medium access control for a wireless collision channel, based on a receiver with adaptive multiuser detection capability, is capable of providing significantly better performance than classical Aloha. The basic features of such a system are multipacket reception (MPR) capability, and the ability (with high probability) to estimate the number of contending users even when the packets are not successfully received. We provide an analytical model that includes these features, and use it to derive methods for backlog estimation and stabilization. Two classes of users are considered: high priority users with quality of service (QoS) requirements, who must succeed within a deadline with a specified probability; and low priority users whose throughput we wish to maximize, while maintaining the QoS for high priority users, and keeping the overall system stable. We obtain contention policies that ensure QoS and stability, based on backlog estimates obtained by extending Rivest's pseudo-Bayesian technique for classical Aloha. The channel throughput and the achievable QoS is characterized as a function of the arrival rates for high and low priority users. Finally, we apply these methods to simulations of a system employing differential minimum mean squared error (DMMSE) adaptive multiuser detection, and find that the analytical model provides accurate guidelines for design and performance predictions.