On the SER of Fixed Gain Amplify-and-Forward Relaying with Beamforming in Nakagami-m Fading

We derive the exact and asymptotic symbol error rate (SER) of multiple-input multiple-output (MIMO) relaying with a fixed gain amplify-and-forward (AaF) relay in Nakagami-m fading channels. We demonstrate that both fixed and variable gain relaying achieve the same diversity, which is jointly determined by the number of antennas and the per-hop fading parameters. We further quantify the performance gap between fixed and variable gain relaying in terms of their array gains. We prove that this gap diminishes as the first and the second hops exhibit highly asymmetric channel qualities.