Cooperative Communications in the Fading Channel

Cooperative coding is a communication paradigm that pools distributed resources of different nodes in a network, such that the nodes act like a collaborative system instead of greedy adversarial participants. Cooperation has shown promise in increasing throughput and providing better power efficiency in wireless networks. In this work, we consider a basic example of cooperation communication, relay coding, and consider methods to improve the power efficiency by employing feedback and using power control. We consider power control policies based on the degree of transmitter channel knowledge. First, when perfect feedback is available, we show results for the optimal power control policy for any network code. We show that by using the decode and forward relaying protocol, in some cases it is possible to approach the universal lower bound on the outage probability for the block fading relay channel. Second, when a finite rate of feedback is available, we see that only a few feedback bits are necessary to achieve most of the gains that the perfect feedback policy has over constant power transmission. Based on these results, it is evident that future network protocols should utilize feedback in order to fully exploit the potential gains of network coding.