Optimal resource allocation for Gaussian relay channel with energy harvesting constraints

In this paper, we study the three-node Gaussian relay channel with decode-and-forward (DF) relaying, in which the source and relay nodes transmit with power drawn from energy-harvesting sources. Assuming a deterministic energy-harvesting model under which the energy arrival time and the harvested amount are known prior to transmission, the throughput maximization problem over a finite horizon of N transmission blocks is investigated. We consider the nodelay-constrained (NDC) traffic case, for which the relay can store the decoded information from the source with arbitrary delay before forwarding it to the destination in each N-block transmission. Although the formulated problem is non-convex, we prove the optimality of a separation principle for the source and relay power allocation over time, based upon which a two-stage algorithm is developed to obtain the optimal source and relay power profiles separately.