MIMO Precoding Structures for Frequency-Flat and Frequency-Selective Fading Channels

This paper presents optimum MIMO precoder designs based on transmit and receive correlation matrices to maximize the ergodic channel capacity for both frequency-flat and frequency-selective fading channels. It is shown that the optimum MIMO precoder in a frequency-flat fading channel is an eigen beamformer with beams referred to the eigenmodes of the transmit correlation matrix. By using the multi-path representation of a frequency-selective fading channel, the corresponding optimum precoding structure is derived. For a frequency-selective fading channel that can be represented by L uncorrelated effective paths, the optimum precoding structure consists of P+L parallel eigenbeamformers. Simulation results show that the proposed precoders can improve the ergodic capacity of both frequency-flat and frequency-selective fading channels, especially for channels with high spatial correlation.