Optimal Scheduling and Power Allocation for Two-Hop Energy Harvesting Communication Systems

Abstract

Energy harvesting (EH) has recently emerged as a promising technique for\ngreen communications. To realize its potential, communication protocols need to\nbe redesigned to combat the randomness of the harvested energy. In this paper,\nwe investigate how to apply relaying to improve the short-term performance of\nEH communication systems. With an EH source and a non-EH half-duplex relay, we\nconsider two different design objectives: 1) short-term throughput\nmaximization; and 2) transmission completion time minimization. Both problems\nare joint scheduling and power allocation problems, rendered quite challenging\nby the half-duplex constraint at the relay. A key finding is that directional\nwater-filling (DWF), which is the optimal power allocation algorithm for the\nsingle-hop EH system, can serve as guideline for the design of two-hop\ncommunication systems, as it not only determines the value of the optimal\nperformance, but also forms the basis to derive optimal solutions for both\ndesign problems. Based on a relaxed energy profile along with the DWF\nalgorithm, we derive key properties of the optimal solutions for both problems\nand thereafter propose efficient algorithms. Simulation results will show that\nboth scheduling and power allocation optimizations are necessary in two-hop EH\ncommunication systems.\n