Performance of Asynchronous Multiple Access MIMO OFDM Systems

This paper investigates the performance of orthogonal frequency division multiplexing (OFDM) based asynchronous multiple access multiple input multiple output channels. In an asynchronous mode of data transmission, independent decoding without user cooperation is a more appropriate approach. Thus, various suboptimal transmitter diversity techniques such as space-time block coding and beamforming are employed, and their performances are evaluated. The average signal to interference and noise ratio (SENR) resulting from linear minimum mean squared error (MMSE) combining is exploited to compute symbol error rate. Simulation results demonstrate that space-time block coding hardly achieves substantial transmitter diversity gains in asynchronous channels. Moreover, receiver diversity is an important factor of the overall performance in a large system. However, beamforming, which uses only part of existing spatial dimensions, can improve the bit- and symbol-error rate performance in the low signal-to-noise ratio (SNR) region where practical communication systems are operated