OFDM AF Variable Gain Relay System for the Next Generation Mobile Cellular

In this paper we present analytical performance evaluation of a dual-hop OFDM amplify-andforward (AF) variable gain (VG) relay system implementing ordered subcarrier mapping (SCM) at the relay station (R), considered to be a very interesting solution for the next generation mobile cellular networks. A scenario with no direct communication between the source of information (S) and destination terminal (D), with the Rayleigh fading statistics on both hops is assumed. A closed form analytical expression for the bit error rate (BER) performance of the considered system with DPSK modulation is derived, while for its ergodic capacity performance, a tight upper bound expression is obtained. The accuracy of the undertaken analytical approach is confirmed through comparison with simulation results. It is shown that significant capacity enhancement can be achieved through SCM implementation at R, for all the signal-to-noise ratio (SNR) values on both hops, but especially in the region of small SNRs on hops. BER analysis reveals that in the region of small and medium average SNRs on both hops BER performance may also be improved with SCM at R station.