Linear Dispersion Codes for Limited Feedback Channels with Feedback Impairments

Linear dispersion codes (LDCs) are an attractive tool for attaining spatial diversity in OFDM systems with multiple transmit antennas. To reach the potential gains, in each situation, the selection of a proper set of codes depends, in general, on the existence of a reliable feedback channel. We propose LDCs for multiple-input multiple-output (MIMO) channels with a fixed amount of feedback. The proposed scheme selects the LDC from a set of LDCs that minimizes the error probability based on the instantaneous channel conditions. The determination of the best set of LDCs is described as a constrained optimization problem. We present several good sets of LDCs, obtained from an optimization algorithm. Through simulation results we show that the proposed schemes outperform previously reported comparable results, yet at the price of increased complexity. We also show the performance gains that can be reached in practice with LDC, by critically evaluating the feedback channel impairments, such as errors and signalling delays, and also considering the effect of signalling overhead on the achievable throughput.