Efficient Sequential Mutiuser Detection for Uplink OFDM/SDMA Systems

An orthogonal frequency division multiplexing (OFDM) system combined with space division multiple access (SDMA) is considered as a spectral efficient transmission scheme. However, the computational effort is very intensive to achieve the near ML performance. In this paper, we propose a computationally efficient sequential multiuser detector using a stack algorithm for uplink OFDM/SDMA systems. The proposed scheme has a structure with three interrelated procedures, namely preprocessing, stack-based tree searching, and optimal sequence selection. In order for complexity to be reduced with achieving appropriate performance, the proposed scheme is designed to search branches with constrained stack size. Simulation results show that the proposed algorithm yields the average bit error rate (BER) performance close to that of sphere decoding (SD) applied to OFDM/SDMA systems with significant saving in complexity.