On the Ergodic Capacity of Dual-Hop OFDM based DF Relay System with Subcarrier Mapping

In this paper ergodic capacity analysis of the dual-hop OFDM decode-and-forward (DF) relay system implementing subcarrier mapping (SCM) at the relay station (R) has been conducted. A scenario with no direct communication between the source of information (S) and destination terminal (D), with Rayleigh fading statistics on both hops is considered. Closed form expression for the achievable ergodic capacity in the case of equal average signal-to-noise ratios (SNRs) on both hops is derived, while for the case of unequal average SNRs on hops a tight upper bound is obtained. Comparison with the simulation results has confirmed the accuracy of the undertaken analytical approach. The obtained results have shown that significant capacity enhancement is achieved through implementation of best-to-best SCM (BTB SCM) scheme, even in the case when the average SNRs on hops are significantly different. Having in mind that this SCM scheme also improves bit error rate (BER) performance of the considered system, then it can be recognized as a very interesting solution for 4G cellular systems.