Optimal pre-weighting scheme for spatially correlated MIMO-OFDM wireless system with subcarrier cluster constraint

Instead of using eigen-beamforming approach to increase capacity gain, an optimal pre-weighting scheme is employed in the closed-loop multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (MIMO-OFDM) wireless system design under subcarrier cluster constraint. This scheme adopts an up-link scale weight vector on the space-time block code (STBC) signals in accordance to its space-time constellation, without utilizing the transmit channel state information (TCSI). Hence, a Bayes decision algorithm is considered to generate the optimum weight vectors using channel coefficients measured from pilot subcarriers in each MIMO sub-channel. Analytical expressions of the signal-to-noise power ratio (SNR) improvement are derived over spatially correlated MIMO fading channels. Inter-subcarrier-interference (ISI) caused by the Doppler effect was also taken into account to evaluate the channel robustness enhancement. Our Monte Carlo simulations show that the proposed scheme outperforms the Alamouti detection scheme in terms of the bit-error-rate (BER) performances of QPSK and 16QAM, respectively, with respect to various pilot intervals. The maximizing eigenvalue distributions (EVD) also validate our results.