Variable-rate variable-power MQAM for energy harvesting communications with 1-bit feedback

In this paper, we propose online discrete rate and power adaption policies based on 1-bit channel feedback for energy harvesting (EH) communications. The receiver (RX) periodically sends 1-bit feedback by comparing the channel power gain with a predetermined threshold. The transmitter (TX) correspondingly adjusts M-ary quadrature amplitude modulation (MQAM) level and transmission power based on the 1-bit feedback and available battery energy. To determine the optimal channel threshold, adaptive MQAM level and corresponding power allocation, we formulate a constrained optimization problem to maximize the throughput within a finite horizon. We show that this problem follows a Markov decision process and can be solved via backward induction method. To alleviate the complexity of the backward induction method, we further propose a suboptimal policy. Simulation results show that the optimal policy has higher throughput than the suboptimal policy, but the performance advantage is negligible.