  In this paper, outage performance of network topology-aware distributed
opportunistic relay selection strategies is studied with focus on the impact of
different levels of channel state information (CSI) available at relays.
Specifically, two scenarios with (a) exact instantaneous and (b) only
statistical CSI are compared with explicit account for both small-scale
Rayleigh fading and path loss due to random inter-node distances. Analytical
results, matching closely to simulations, 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 the same diversity order is associated with a clear
performance degradation at low SNR due to splitting of system resources between
multiple relays.
