Outage-optimal threshold-based opportunistic cooperation in AF relaying systems with staying link information

Opportunistic cooperation (OC) dynamically switches between a cooperative mode (CM, using both direct and relay links) and a non-cooperative mode (NM, using only the direct link). OC achieves significant power gain compared with using CM only but needs full channel information. In this paper, we propose threshold-based OC (TBOC) in an amplify-and-forward (AF) relaying system where only partial channel information, so-called staying link information (SLI), is available and the switching-decision is made by comparing the SLI with a threshold to be determined. We consider three variants of TBOC and provide optimal thresholds, respectively. It is proved that the outage probabilities of the proposed TBOCs with the optimal thresholds are exactly the same to that of OC with full channel information. Numerical results are also provided to verify the analysis and to give insights on the outage performance of the TBOC.