Capacity of the OFDM AF VG relay systems in Rayleigh fading channels

In this paper, an analitycal expression for the upper bound of the achievable capacity of OFDM amplify-and-forward (AF) relay system with two hops, implementing variable gain (VG) and BTB (Best-to-Best) subcarrier mapping (SCM) scheme at the relay (R) station, is derived. Scenario with the three communication nodes is considered, without direct communication between the source of information (S) and destination node (D), while the fading statistics on both hops is assumed to be Rayleigh distributed. The validity of undertaken analytical approach is confirmed through the comparison of the obtained results with the simulation results. The attained results have shown that significant capacity enhancement can be achieved in considered relay system through BTB SCM (up to 30%), especially in the region of small signal-to-noise ratios.