Investigation of multiuser detection schemes for Multiple Transmit/Multiple Receive antenna aided OFDM-SDMA systems

Multiple Transmit-Multiple Receive (MTMR) Orthogonal Frequency-Division Multiplexing /Space-Division Multiple Access (OFDM-SDMA) systems have recently attracted significant interests among researchers and developers because of its potentials for realizing spectrally-efficient wireless services at low complexity and costs. However, in multiuser MTMR systems, multiuser detection (MUD) techniques become more challenging, owing to the increased number of independent transmitter-receiver links, especially with multiple antennas at both ends. This paper investigates the performance of adaptive beamforming schemes suitable for multiuser MTMR OFDM-SDMA systems where both mobile users and base stations employ multiple transmit antennas. Using performance criteria such as mean-squared error (MSE) and signal-to-interference-plus noise ratio (SINR), we evaluate the performance of MTMR maximum ratio combining (MTMR-MRC) and the MTMR minimum mean-squared error (MTMR-MMSE) systems. In both schemes, it is shown that the level of interference dominates the detection of users´ signal causing high error floor at low SINR and imposing restrictions on the number of transmit antennas.