Strategic Versus Collaborative Power Control in Relay Fading Channels

Relaying is often advocated for improving system performance by enhancing spatial diversity in wireless networks. Relay nodes make contributions to improving the source-destination link quality by sacrificing their own energy. In this paper, we address the issue of energy tradeoff made by relay nodes between transmitting their own data and forwarding other nodes´ information in fading channels. Assuming channel state information (CSI) on fading amplitudes is perfectly known to both transmitters and receivers, we propose two power control and relaying policies. One is based on a strategic motivation, where each node functions as a relay and minimizes its own energy expenditure while meeting the outage probability requirement of all nodes. The second approach is based on complete collaboration, where the total energy consumption across all nodes is minimized. Numerical results demonstrate a significant impact of CSI on energy saving in relaying as compared with the relaying scheme without power control. In most cases, collaborative relaying dominates over the non-cooperative strategic one in the sense that the former not only minimizes total energy but also reduces individual energy expenditure of all nodes. This implies once forwarding and relaying is adopted across various nodes, exchanging of CSI becomes crucial, and collaborative energy minimization rather than the non-cooperative strategic approach should be pursued