Effect of Feedback Delay on Downlink Amplify-and-Forward Relaying with Beamforming

In relay networks, partial channel state information at the transmitter due to feedback delay can severely degrade the beamforming performance. In this paper, the decremental effect of transmit beamforming with feedback delay on the downlink performance of a two hop Amplify-and-Forward (AF) relay network over Rayleigh fading channels is investigated. The source is equipped with multiple antennas while the relay and the destination has a single antenna. We have derived closed-form expressions for the outage probability, probability density function of the received signal-to-noise ratio (SNR) at the destination and the average bit error rate (BER). To gain further insights, outage probability and average BER approximations at high SNR are also presented. Numerical results supported by simulations are provided to illustrate the decremental effects feedback delay on the performance of the considered AF relay system.