Optimizing Energy Allocation for Energy Harvesting Node with Hybrid ARQ

—Efficiently using scarce energy is more critical for the nodes which are supplied by energy harvesting. However, it is difficult to optimize the transmit energy of each retransmission when future Channel State Information (CSI) and accurate retransmission number cannot be obtained in Hybrid Automatic Repeat Request (HARQ) system. In this paper, we propose a novel HARQ scheme to allocate the battery can be recharged from received signals. In the proposed scheme, the amount of energy used in each transmission is selected to maximize a utility function which is defined as the conditional throughput divided by the energy consumption of this transmission, i.e., instantaneous energy efficiency. To simplify the operational complexity of EHN, a suboptimal closed form solution is also presented. Simulation results demonstrate that the proposed HARQ scheme can improve both energy efficiency and normalized throughput significantly.