Wireless Powered Relay Networks: Rate Optimal and Power Consumption-Aware WPT/SWIPT

Abstract

We focus on the rate-optimal design of Wireless Powered Relay Networks (WPRNs) and propose a new cooperative communication scheme. Our scheme employs multiple wireless powered Amplify and Forward (AF) relays and relay selection and combines Time Splitting (TS), with Antenna Switching (AS) and Self Energy Recycling (SER). It consists of an initial Wireless Power Transfer (WPT) subframe, followed by a cooperative transmission subframe, during which one antenna is used for Energy Harvesting (EH) and SER and the remaining ones are used for data reception and data forwarding. For this scheme, we present solutions to the problems of 1) rate-optimal beamforming (BF) design, 2) rate-optimal, joint Harvesting Antenna Selection (HAS), BF design, and WPT subframe duration determination. Our solutions build on a generic piecewise linear EH model, which allows us to closely approximate the characteristics of different non linear EH measurements and models, by selecting the number of piecewise linear components and their parameters. In addition, we consider a realistic power consumption model at the relays that accounts for both transmit and circuit power consumption. Moreover, our BF solution is optimal and requires solving a set of simple optimization problems, where the solution of each one of them can be found in a simple closed form. Thus, it is characterized by low implementation complexity, and avoids sophisticated iterative optimization methods. To the best of our knowledge, this work is the first one to introduce a scheme, which combines TS, AS, and SER principles and exploits realistic EH and power consumption models at the relays. Finally, we assess the performance of our scheme over fading channels and find that it outperforms existing solutions that use the same hardware.