Covariance precoding schemes for MIMO OFDM over transmit-antenna and path-correlated channels

This paper considers covariance-feedback based linear precoding (LP) and nonlinear Tomlinson-Harashima precoding (THP) for multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. Orthogonal space time block coded (OSTBC)double dagger OFDM and spatially-multiplexed (SM) OFDM are analysed. The main objective is to design precoders to mitigate the impact of transmit-antenna and path correlations. The impact of path correlations on the pairwise error probability (PEP) of MIMO OFDM is also analysed. Closed-form, waterfilling-based covariance precoders are derived to minimize the worst case PEP in OSTBC OFDM. An adaptive transmission strategy is also developed for switching between precoded SM OFDM and precoded OSTBC OFDM. The switching criterion is the minimum Euclidean distance of the received codebook. The switching decision sent to the transmitter requires one feedback bit per subcarrier. The proposed precoders considerably reduce the error rate in antenna and path-correlated channels; nonlinear precoders perform better than linear precoders. We show that the adaptive strategy can achieve full diversity gain, and it outperforms either SM or OSTBC applied individually in terms of the bit error rate (BER). Copyright (C) 2010 John Wiley & Sons, Ltd.