Spatially efficient distributed relay selection for random relay networks

In the presence of a large number of relays, some effective relays close to the source and destination nodes need to be regionally elected and the relays far from them shall be disregarded for relay selection process because of the likelihood of higher outage probability. In this paper, we propose an opportunistic feedback mechanism combining a geographical selection region where the relay whose effective channel gain is above a pre-determined threshold can only feed back, and thereby establish a relation between required relay-node density and the level of feedback threshold. It is shown that required relay-node density and selection region for a desired quality-of-service (QoS) depend on the feedback threshold.