Performance analysis of multi-relay selective DF based OFDM cooperative systems over time selective links with imperfect CSI

This paper considers an Orthogonal Frequency Division Multiplexing (OFDM) based selective decode-and-forward (DF) cooperative communication system with multiple mobile relays between the mobile source and destination. Closed form expressions have been derived for the average end-to-end SER and also the asymptotic error floor considering a Rayleigh faded correlated multi tap channel with time selectivity due to node mobility and imperfect channel estimates for the source-destination, source-relay and relay-destination links. Further, a framework is also developed for optimal power allocation for a given total system power budget. Simulation results have been presented to illustrate the system performance for various OFDM channel and mobility conditions and also to verify the analytical results derived. Furthermore, it is demonstrated that optimal power allocation leads to a performance improvement in comparison to the conventional equal power allocation especially in the low and moderate SNR regimes. At high SNR, the system performance with both optimal and equal power allocation can be seen to approach an asymptotic floor, since the system performance is independent of the power of the noise components, which is also supported by the analysis.