Optimizing Energy Harvesting Decode-and-Forward Relays With Decoding Energy Costs and Energy Storage

Energy harvesting (EH) relay communication systems with decoding energy costs in multiple block cases have not been widely studied. This paper investigates the relay network with a decode-and-forward relay powered by EH. Unlike other works, we consider the relay with energy decoding costs which harvests random energy from both a dedicated transmitter and other ambient radio-frequency (RF) sources. The EH relay adopts a harvest-receive-forward time-switching architecture. We optimize the time fractions of the three phases and the reception rate at the relay to maximize the offline throughput for single and multiple block cases under two EH scenarios. The multi-block optimization problem constitutes a complex non-convex problem, which we decouple into a single block problem with two auxiliary variables determined by an outer optimization problem. The original problem is finally solved at the cost of linear optimization after series of tricks. Several conclusions are derived: (i) energy storage is necessary (unnecessary) when the relay harvests energy from the transmitter (ambient RF sources), (ii) the optimal reception rate remains unchanged, while the optimal time fractions vary with the energy harvested from ambient RF sources leading to different average throughput. We give numerical simulations to verify our theoretical analysis.