New solution for BER performance improvement of OFDM AF relay systems

Dual-hop OFDM amplify-and-forward (AF) variable gain (VG) relay systems may improve bit error rate (BER) performance if ordered subcarrier mapping (SCM) is applied at the relay station (R). In previous works we showed that in the region of small and medium 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 high values of average SNRs on hops very small BER performance improvement is achieved by implementing best-to-worst SCM (BTW SCM) scheme. In this paper we propose new solution, where in the assumed relay system with BTB SCM the subcarriers having the lowest SNR on each hop are omitted. Analytical and simulation result comparison, for the scenario with DPSK modulation implemented and Rayleigh fading statistics on both hops, have confirmed that the proposed solution achieves the best BER performance for all the SNR values.