Non-unitary precoder design for reducing feedback overhead in MIMO-OFDM systems

The precoder feedback overhead in MIMO-OFDM systems is heavy as the number of subcarriers is usually large. Most of the current limited feedback works focus on unitary precoding schemes. Based on the fact that the channel matrices of neighboring subcarriers in MIMO-OFDM systems are correlated, an alternative transceiver is proposed here. In this paper, non-unitary precoders shared by several adjacent subcarriers, and the corresponding individual equalizers are jointly designed under partial CSI. As the number of precoding matrices is smaller, the feedback overhead can be reduced. The transceivers are designed to minimize the detection mean-squared error (MSE) under the total transmit power constraint. A convergent iterative algorithm based on the Lagrange multipliers method is proposed. The necessary conditions for an optimal transceiver, Karush–Kuhn–Tucker (KKT) conditions, are satisfied in each iteration. Numerical results under the frequency-selective MIMO-OFDM channel, which is generated by the classical Zheng and Xiao's model, prove that the proposed transceiver can significantly reduce the feedback overhead without severe performance degradation.