NOMA Throughput and Energy Efficiency in Energy Harvesting Enabled Networks

An energy harvesting (EH) enabled network is capable of delivering energy to users, who are located sufficiently close to the base stations. However, wireless energy delivery requires much more transmit power than what the normal information delivery does. It is very challenging to provide the quality of wireless information and power delivery simultaneously. It is of practical interest to employ non-orthogonal multiple access (NOMA) to improve the network throughput, while fulfilling the EH requirements. To realize both the EH and information decoding, this paper considers a transmit time-switching (transmit-TS) protocol. Two important problems of users' max-min throughput optimization and energy efficiency maximization under power constraint and EH thresholds, which are non-convex in beamforming vectors, are addressed by efficient path-following algorithms. In addition, the conventional power splitting (PS)-based EH receiver is also considered. The provided numerical results confirm that the proposed transmit-TS-based algorithms clearly outperform the PS-based algorithms in terms of throughput and energy efficiency.

I. Introduction

Radio frequency (RF) energy harvesting (EH) [1]–[3] has emerged as a potential technology to energize the Internet of things. To realize both wireless EH and information decoding (ID), the users need to split the received signal for EH and ID either by power splitting (PS) or time switching (TS), where the latter is referred to as “receive-TS” [1], [4], [5]. PS has been shown mostly outperforming receive-TS but it is complicated and inefficient for practical implementation. Recent findings in [4], [6] and [7] demonstrate the advantages of the new “transmit-TS” approach over the PS approach, where information and energy are transferred separately so the users do not need any sophisticated device for EH.