BER performance enhancement in OFDM AF fixed gain relay systems

We analysed bit error rate (BER) performance of dual-hop OFDM amplify and forward (AF) relay system with fixed gain (FG) at relay station (R), implementing ordered subcarrier mapping (SCM) at R. A scenario with Rayleigh fading statistics on both hops is assumed. In previous works we showed that in the region of small values of average signal-to-noise ratios (SNRs) on hops best-to-best SCM (BTB SCM) scheme should be applied, while in the region of medium and high values of average SNRs on hops, BER performance improvement is achieved by implementing best-to-worst SCM (BTW SCM) scheme. In this paper we analysed new solution, where in the assumed relay systems with SCM, one or more subcarriers having the lowest SNRs on each hop are omitted. Besides, we examined power balance of the system implementing SCM through comparison of BER performance expressed as a function of power transmitted per subcarrier, with BER performance of the ordinary OFDM AF FG relay system, as well as with the performance in case of direct transmission between source of information (S) and destination terminal (D).