Effect of Channel-Estimation Error on BER Performance in Cooperative Transmission

In this paper, a framework for evaluating the bit-error-rate (BER) performance of amplify-and-forward (AF) relay-assisted cooperative transmission is provided in the presence of imperfect channel estimation. First, the AF relaying is classified into two cases - a variable gain and a fixed gain. For each case, the closed-form average BER is derived by using the moment-generating function (MGF) of the effective output SNR, which quantifies the SNR penalty due to the noisy channel estimate. Moreover, the asymptotic BER bound is also provided at a high SNR regime for the insight of our approach. In particular, the effect of the feedforward delay on informing the source-relay channel estimate as to the destination is presented in the variable-gain relay. Numerical investigation shows that the analytic result makes an exact match with the simulation, and the comparative superiority between the fixed- and variable-gain relay is discussed.