Mean Mutual Information Per Coded Bit Based Precoding in MIMO-OFDM Systems

This work proposes a per-subband multiple input multiple output (MIMO) precoder selection technique for point-to-point MIMO orthogonal frequency division multiplexing (OFDM) based bit interleave coded modulation (BICM) systems with the soft-output minimum mean square error (MMSE) receiver. Given a pre-designed precoder codebook, the codeword/precoder that maximizes the mean of the mutual information per coded bit (MMIB) on all subcarriers within a subband is selected. The main advantages of this technique are the following: i) the precoder selection metric is explicitly related to BICM performance, thus it outperforms the previously proposed precoding techniques; ii) with commonly used unitary precoding codebooks, this technique works for an arbitrary number of transmit streams unlike the minimum singular value based method which does not work when the number of input streams is the same as the number of transmit antennas; iii) when multiple packets are transmitted and one precoder is used for these transmitted packets, an algorithm that combines the MMIB of each packet is proposed using an upper bound on the average packet error rate.