Optimal Cooperative Power Allocation for Energy-Harvesting-Enabled Relay Networks

In this paper, we present a new power-allocation scheme for a decode-and-forward (DF) relaying-enhanced cooperative wireless system. While both the source node (SN) and relay node (RN) have limited energy storage, the SN can also draw power from the surrounding radio-frequency (RF) signals. In particular, we assume a deterministic RF energy-harvesting (EH) model under which the signals transmitted by the relay serve as the renewable energy source for the SN. The amount of harvested energy is known for a given transmission power value of the forwarding signal and channel condition between the SN and RN. To maximize the overall throughput while meeting the constraints imposed by the initially stored energy and the renewable RF energy source, an optimization problem is formulated and solved. Based on different harvesting efficiency values and channel conditions, closed-form solutions are derived to obtain the optimal joint source and relay power allocation. It is shown that, instead of demanding high on-grid power supply or high green energy availability, the system can achieve compatible or higher throughput by utilizing the harvested energy.