Precoding scheme based on constellation rotation for MISO systems

The error probability of a maximum-likelihood (ML) detector depends on the signal-to-noise ratio (SNR) and distances between each possible combined channel-transformed constellation (CCTC) point and its nearest neighbours. Among these distances, the minimum one dominates the bit-error rate (BER) performance. This paper proposes a precoder based on constellation rotation (CR) for multiple-input-single-output (MISO) systems armed with an ML detector, maximising the minimum distance according to the channel information optimally. With the proposed precoder, the BER performance of MISO systems is boosted remarkably in both quasistatic Rayleigh fading independent and correlated channels. Through systematic analysis, closed-form solutions of the optimal CR angle are derived for 2 × 1 MISO systems employing BPSK or QPSK. Simulation results demonstrate that there is performance improvement of at least 2 dB with the new 2 × 1 MISO system employing BPSK, and the improvement reaches at least 3dB when QPSK is employed. In addition, the new 2 × 1 MISO system outperforms the traditional one in correlated channels significantly.