Energy efficiency optimization in relay-assisted networks with energy harvesting relay constraints

In this paper we consider data transmission in a decode-and-forward (DF) relay-assisted network in which the relay is energy harvesting (EH) powered while the base station (BS) is power-grid powered. Our purpose is to maximize the BS´s energy efficiency (EE) while making full use of the relay´s renewable energy and satisfying the specific average throughput requirements. In contrast to existing literature on energy harvesting system which only considers the radio transmission power, we take the static circuit power into account as well. We formulate the EE optimization problem and prove that the EE of the BS and relay are both quasiconvex in the instantaneous transmission rate. Then we divide the complex optimization problem into two point-to-point link level optimization parts and propose an energy-efficient resource allocation (EERA) scheme in which power control and sleep mode management are jointly used. The simulation results demonstrate that EERA may achieve good energy saving effects. We also compare the EE of an energy harvesting relay system with a power-grid powered one and provide more insight into the EE problem of energy harvesting relay system.