Multiuser Detection for Random Access Bandwidth Request in WiMAX

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 machineto-machine (M2M) devices pre-equalize their random access codes by using the estimated frequency response of the slowly time-varying wireless channel. Consequently, we develop a lowcomplex multiuser detection algorithm. The 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 some efficient decoder design procedures which enhance the user detection performance. The performance of the proposed schemes is demonstrated in a WiMAX network environment.