Cooperative Relay in Cognitive Radio Networks: Decode-and-Forward or Amplify-and-Forward?

Cognitive radios (CR) and cooperative communications represent new paradigms that both can effectively improve the spectrum efficiency of future wireless networks. In this paper, we investigate the problem of cooperative relay in CR networks for further improved network performance. The objective is to provide an analysis for the comparison of two representative cooperative relay strategies, decode and forward (DF) and amplify and forward (AF), in the context of CR networks. We consider optimal spectrum sensing and p-Persistent CSMA for spectrum access, and derive closed-form expressions for network-wide throughput achieved by DF and AF. Our analysis is validated by simulations. We find each of the strategies performs better in a certain parameter range; there is no case of dominance for the two strategies. The considerable gaps between the cooperative relay results and the direct link results exemplify the diversity gain achieved by cooperative relays in CR networks.