Multiuser Detection for Random Access Bandwidth Request in WiMAX

Abstract

Random access is a multiple access communication protocol where the users simultaneously communicate with a base station (BS) in an uncoordinated fashion. In this work, we consider the problem of multiuser detection in a random access bandwidth request context. We propose an enhanced random access scheme where the fixed/low-mobility M2M devices pre-equalize their random access codes using the estimated frequency response of the slowly-varying wireless channel. Consequently, we have developed two different multiuser detection algorithms. The first algorithm works in a greedy fashion where it performs cross-correlation of the received signal with a set of decoder sequences and detects active users based on the correlation output. We derive the condition under which the algorithm can detect a given number of active users with high probability. Subsequently, we demonstrate an efficient decoder design procedure which enhances the user detection performance. A basis mismatched sparse recovery technique has been applied in the second algorithm which exploit an inherent structure of the random access protocol. The performance of the proposed schemes is demonstrated in a WiMAX network environment.