On channel estimation of orthogonal frequency-division multiplexing amplify-and-forward cooperative relaying systems

This study investigates channel estimation for amplify-and-forward (AF) relaying systems. For a two-hop relaying system, channel estimation of a relay path (source-relay-destination) with AF relaying is unique because both individual source-to-relay (S-R) and relay-to-destination (R-D) links are necessary at the destination to perform the optimum combination of signals received from the direct path (source-to-destination) and relay path if employing a cooperative diversity transmission. Until now, most literature about channel estimation on relaying systems has focused on the composite channel of the relay path, and not its individual links. Current methods to separate the estimation of both individual links require the relay to either deliver a quantised version of the S-R link estimate through an independent feed-forward channel, or to perform discrete Fourier transform/inverse discrete Fourier transform operations before amplifying the received signals. In this study, the respective channel estimations are done at the destination. First, the destination utilises a relay amble (R-amble) to obtain channel estimation of the R-D link. Next, exploiting the R-D link estimate, a maximum-likelihood estimator is proposed for the S-R link in a decision-directed (DD) way. Simulation results show that the proposed scheme out performs the current relay-assisted methods in most circumstances. In addition, numerical results reveal that the mean-square error can be significantly reduced in a DD way for symbol error rates of interest.