Energy Efficiency Optimization in Energy Harvesting Incremental Relay System

In this paper, according to the energy efficiency (EE) definition based on packet transmission, we analyze the energy efficiency in energy harvesting incremental relay system with energy harvesting constraints. Our purpose is to maximize energy efficiency of source node while making full use of relay's harvested energy. First, we consider the energy efficiency of pointto-point link with multilevel quadrature amplitude modulation (MQAM) and derive the energy efficiency definition based on packet transmission. Next, the energy efficiency optimization problem in incremental relay system is formulated. To solve the problem, we discuss two factors that affect energy efficiency: transmission power and packet length. Furthermore, we propose a joint transmission power and packet length iterative optimization algorithm and give an intuitive analysis of convergence. Finally, simulations have been carried out to verify the benefits of the proposed algorithm, which can significantly improve energy efficiency compared with only transmission power optimized scheme or only packet length optimized scheme.