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

TL;DR

This paper explores optimal scheduling and power allocation strategies for two-hop energy harvesting communication systems, demonstrating how directional water-filling guides design and improves performance under energy randomness.

Contribution

It introduces a novel application of directional water-filling to two-hop EH systems and develops efficient algorithms for joint scheduling and power allocation.

Findings

Directional water-filling guides optimal design.

Joint scheduling and power allocation improve performance.

Algorithms outperform non-optimized schemes.

Abstract

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