WLC42-5: Adaptive Precoding for Switching between Spatial Multiplexing and Diversity in MIMO OFDM with Transmit Antenna and Path Correlations

The path and antenna correlations significantly degrade the system capacity in spatially-multiplexed multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems and increase bit error rate (BER) in orthogonal space-time block coded (OSTBC) OFDM. We develop adaptive dual-mode precoding to improve system performance with transmit antenna and path correlations. Both linear and non-linear Tomlinson-Harashima (TH) precoders are considered. In our proposed approach, precoding for maximizing capacity in spatially-multiplexed OFDM or precoding for minimizing error rate in OSTBC OFDM, is adaptively chosen at the receiver, and only one-bit decision information per subcarrier needs to be sent back to the transmitter. The precoding mode selection depends on the channel conditions. To determine the precoding matrix only the statistical knowledge of the channel is needed at the transmitter, which significantly reduces the feedback requirements. In spatially correlated channels, proposed adaptive dual-mode precoding individually outperforms either capacity- maximization precoding in spatially-multiplexed OFDM or error-rate-minimization precoding in OSTBC OFDM.