A diversity analysis for block-fading Amplify-and-Forward systems

In this paper, we deal with the performance of nonorthogonal Amplify-and-Forward (NAF) protocols over block-fading channels. In contrast with previous studies, which assume that the channel remains constant over the whole cooperative frame, here we relax this constraint and assume a block fading channel which changes during the cooperation. Despite this additional channel diversity degree, channel inversion amplification schemes are unable to increase the diversity gain of the system due the high correlation between the two simultaneous diversity branches. We propose a fixed gain amplification factor which efficiently uses the additional diversity degree of the channel and recovers the diversity loss associated with channel inversion schemes. The diversity analysis is based on some well-defined capacity bounds which follow the diversity order of the true capacity.