Opportunistic Decode-and-forward Cooperation in Nakagami-m Fading Channels with Relay Selection

In this paper, the outage performance of opportunistic decode-and-forward cooperation is analyzed in independent but not necessarily identical Nakagami-m fading channels, where the impacts of relay selection criterion, relay number, channel fading severity parameter and the availability of the direct link are studied comprehensively. The closed-form expressions of outage probability in high signal-to-noise ratio region and the diversity order are derived for both asymmetric and symmetric scenarios. The analysis shows that the achievable diversity order is related to the channel fading severity parameter m, the number of relays K, the specific relay selection criterion N and the availability of the direct link. Take symmetric scenario for instance, the diversity order is m (K ? N +?1) if the direct link blocks, otherwise the diversity order becomes m (K ? N +?2). For asymmetric scenario, the diversity order depends on the particular value of fading severity parameter m in each link, and the expression is also derived. Simulation results validate the analysis of outage probability and diversity order.