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On the optimal solution for performance enhancement in infrastructure OFDM relay systems

We derive bit error rate (BER) performance of DPSK modulated dual-hop OFDM amplify-and-forward (AF) relay system with fixed gain (FG) at relay station (R), which implements modified ordered subcarrier mapping (SCM). SCM scheme is modified in sense that one or more subcarriers having the worst channel frequency responses (CFRs) on both hops are omitted, and then SCM is performed at R. Two SCM schemes are considered, i.e. best-to-best SCM (SCM) and best-to-worst SCM (BTW SCM). Scenario with Rayleigh fading statistics on both hops is considered. In order to identify an optimal solution for BER performance improvement in dual-hop OFDM relay systems, the obtained results are compared with the performance of corresponding OFDM AF variable gain (VG) and OFDM decode-and-forward (DF) relay systems, both implementing the same modified ordered SCM. Additionally, we compare ergodic capacity performance of OFDM based AF FG, AF VG and DF relay systems with BTB SCM, in order to define an optimal solution when capacity is performance of interest.