Multiuser detection with an unknown number of active users: Receiver design

In multiuser detection, the set of users active at any time may be unknown to the receiver. In these conditions, optimum reception consists of detecting simultaneously the set of active users and their data, problem that can be solved exactly by applying random-set theory (RST) and Bayesian recursions (BR). However, implementation of optimum receivers may be limited by their complexity, which grows exponentially with the number of potential users. In this paper we examine three strategies leading to reduced-complexity receivers. In particular, we show how a simple approximation of BRs enables the use of Sphere Detection (SD) algorithm, which exhibits satisfactory performance with limited complexity.