Performance analysis of optimal beamforming in AF MIMO relaying over asymmetric fading channels

This paper considers an optimal single stream beamforming for a multiple-input multiple-output (MIMO) relay network with non-coherent dual-hop amplify-and-forward (AF) relaying. The source-relay and relay-destination channels undergo Rayleigh and Rician fading respectively. The channel state information is only available at the destination, and the destination computes the optimal transmit and receive beamforming vectors to maximize the instantaneous signal-to-noise ratio (SNR) at the destination. The optimal transmit beamforming vector will be sent back to the transmitter via a dedicated feedback link. We derive closed-form expressions for the cumulative density function, probability density function, and moments to statistically characterize the properties of the instantaneous SNR. These statistical properties are used to analyze the performance of the system with outage probability, average bit error rate, and ergodic capacity. The results of the performance analysis reveal that Rician factor and number of antennas at the nodes improve the system performance, and the optimal single stream beamforming system provides better error performance than an orthogonal space-time block coded based AF MIMO system.