Symbol-based space diversity for coded OFDM systems

The authors present a coded orthogonal frequency division multiplexing (COFDM) system with multiple-input/multiple-output (multiple transmit and/or multiple receive) antennas for high-rate wireless data transmission. A symbol-based space diversity technique, which can take advantage of the inherent space diversity, is proposed. In contrast to conventional subcarrier-based space diversity, it is shown that the proposed technique can be implemented using only one discrete Fourier transform block and the same weighting coefficients for the whole OFDM symbol. This significantly reduces the system complexity while achieving almost the same diversity order as that of the traditional space diversity approach. They also propose an iterative algorithm to obtain the antenna weighting coefficients. Simulation results show that the proposed algorithm converges fast and approaches the global optimal solution for most channel realizations. It is also shown that, when the proposed technique is employed in a time division duplex scenario, where the uplink and downlink channels are reciprocal, the system complexity can be further reduced.