Performance and Complexity Analysis of Eigencombining, Statistical Beamforming, and Maximal-Ratio Combining

For receive-side maximal-ratio combining (MRC) and maximum-average-SNR beamforming (BF), the wireless-channel fading correlation impacts the symbol-detection performance-decreasing correlation improves/degrades MRC/BF performance-whereas the numerical complexity of these methods is fixed-high/low for MRC/BF. Matching signal processing complexity to the actual correlation conditions and, thus, to the achievable performance is possible with a superset of MRC and BF known as maximal-ratio eigencombining (MREC). For imperfectly known and correlated fading gains, new closed-form expressions are derived for the probability density function of the MREC-output SNR, as well as for the outage probability (OP) and the average error probability. These new expressions permit seamless evaluation for any correlation value of MREC, MRC, and BF performance measures, such as the amount of fading, the deep-fade probability, diversity and array gains, and the OP. Our results confirm that, in realistic scenarios, adaptive MREC can achieve MRC-like performance for BF-like complexity.