Energy Harvesting Cooperative Communication Systems

This paper addresses the problem of throughput maximization in an energy-harvesting two-hop amplify-and-forward relay network. We obtain optimal policies for transmission power for two cases. First, we assume non-causal knowledge of the harvested energy and that of the fading channel states. Then, we assume that this information is known only causally. We propose an effective algorithm to solve the power-use problem in the non-causal (offline) case. For the causal (online) case, we cast the problem as a Markov decision process (MDP) and solve the resulting optimization problem using only causal knowledge of the fading and the harvested energy. This MDP approach yields good performance, but at the cost of computational complexity. To address this issue, we consider the case where the power control at the transmitting nodes is limited to on-off switching. We derive interesting properties for the optimal solutions to the MDP formulation for this special case. Furthermore, using these properties, we propose a computationally simple power allocation scheme. The performances of the proposed schemes are evaluated using computer simulations and are compared to existing methods which address the same problem.