On the impact of relay-side channel state information on opportunistic relaying

Outage performance of network topology-aware opportunistic relay selection is studied using stochastic geometry techniques with the focus on the impact of different levels of channel state information (CSI) available at relays. Specifically, two scenarios with either (a) exact instantaneous or (b) only statistical CSI are compared with an explicit account for both small-scale Rayleigh fading and path loss due to random node locations. Analytical and simulation results suggest that although similar diversity order can be achieved in both cases, the lack of precise CSI to support relay selection translates into significant increase in the power required to achieve the same level of QoS. In addition, when only statistical CSI is available, achieving high diversity order is possible by employing multiple relays at the cost of performance degradation at low SNR due to splitting of system resources.