Capacity Comparison of Orthogonal and Non-Orthogonal Cooperative Relay Systems

For a single relay channel, we study the average throughput of two different amplify-and-forward (AF) protocols, which are orthogonal-AF (OAF) and nonorthogonal-AF (NAF). The NAF protocol has been proposed to overcome a significant loss of performance of OAF in the high spectral efficiency region, and it was also shown that NAF performs better than OAF in terms of the diversity-multiplexing tradeoff. However, the results have been evaluated at the asymptotically high signal to noise ratio (SNR), and the power allocation problem between the source and the relay was neglected. We examine which protocol has a better performance in a practical system operating at a finite SNR. We also study where a relay should be located with consideration of the power allocation. In this paper, we show that the performance depends on both SNR and power allocation ratio, which indicates OAF may perform better in a certain environment.