Reduced Complexity Maximum Likelihood Multiuser Detection for OFDM-Based IEEE 802.11A WLANs Utilizing POST-FFT Mode

Abstract

Considering the space division multiple access (SDMA) in IEEE 802.11a based systems, in this paper, we propose a new two-step multiuser detection (MUD) algorithms. In the first step, MMSE and MSNIR MUD algorithms are used. In the second step, by using sensitive bits algorithm (SBA) to obtain least reliable bits, maximum likelihood detection (MLD) algorithm is applied only to these bits; as a consequence, the search space is reduced dramatically. In order to reduce the computational complexity of MLD algorithm, an innovative modification named the less complex norm approximation (LCNA) based Euclidean distance is used. The performance and complexity of proposed MUD algorithms are compared with nonlinear MMSE-SIC, MSNIR-SIC and ML MUD algorithms. Results show that with a minimal penalty in performance compared to MLD algorithm, the SBA-based proposed two-step schemes have significant reduction in complexity. Furthermore, it is shown that for a specified number of sensitive bits, the introduced algorithms have approximately the same performance with significant less complexity compared to MMSE-SIC and MSNIR-SIC nonlinear MUD algorithms.