Resource Allocation for SWIPT Systems with Nonlinear Energy Harvesting Model

Wei Duan,Yifan Hu,Yizhi Feng,Mingang Liu

doi:10.1155/2021/5576356

Abstract

In this paper, we study the resource allocation for simultaneous wireless information and power transfer (SWIPT) systems with the nonlinear energy harvesting (EH) model. A simple optimal resource allocation scheme based on the time slot switching is proposed to maximize the average achievable rate for the SWIPT systems. The optimal resource allocation is formulated as a nonconvex optimization problem, which is the combination of a series of nonconvex problems due to the binary feature of the time slot-switching ratio. The optimal problem is then solved by using the time-sharing strong duality theorem and Lagrange dual method. It is found that with the proposed optimal resource allocation scheme, the receiver should perform EH in the region of medium signal-to-noise ratio (SNR), whereas switching to information decoding (ID) is performed when the SNR is larger or smaller. The proposed resource allocation scheme is compared with the traditional time switching (TS) resource allocation scheme for the SWIPT systems with the nonlinear EH model. Numerical results show that the proposed resource allocation scheme significantly improves the system performance in energy efficiency.

Highlights

In traditional energy-constrained wireless networks, the wireless devices normally use batteries as energy source and require periodically recharging or replacing the batteries, which is difficult for a large number of wireless devices and even hazardous or impossible in some circumstances [1], resulting limited lifetime of the wireless devices and the networks.Energy harvesting (EH) that allows the energy-limited wireless devices to harvest energy from the ambient environment is a promising solution for extending the lifetime of energy-constrained wireless networks
It is shown in (21) and Algorithm 2 that for the simultaneous wireless information and power transfer (SWIPT) systems with nonlinear EH model, the optimal resource allocation scheme based on the time slot-switching strategy requires that the receiver switches to information decoding when the signal-to-noise ratio (SNR) is larger or smaller, whereas switching to energy harvesting is performed in the region of medium SNR
In order to validate the proposed scheme, we compare the proposed resource allocation scheme with the traditional TS resource allocation scheme [26] in the energy efficiency performance for the SWIPT systems with nonlinear EH model, where the energy efficiency for the traditional TS scheme is obtained by sweeps, the time switching factor from 0 to 1 with a step 0.01, and the energy efficiency is defined as ηE = RðβÞ/ðP − E1⁄2QðβÞÞ: ð23Þ

Summary

Introduction

In traditional energy-constrained wireless networks, the wireless devices normally use batteries as energy source and require periodically recharging or replacing the batteries, which is difficult for a large number of wireless devices and even hazardous or impossible in some circumstances [1], resulting limited lifetime of the wireless devices and the networks.Energy harvesting (EH) that allows the energy-limited wireless devices to harvest energy from the ambient environment is a promising solution for extending the lifetime of energy-constrained wireless networks. Among the EH technologies, simultaneous wireless information and power transfer (SWIPT) takes advantage of the radio frequency (RF) signal’s ability of carrying both information and energy at the same time, providing great convenience of recharging to energy-constrained devices by harvesting energy from the RF signals. In [3], two kinds of SWIPT receivers, namely, time switching (TS) and power splitting (PS) receivers, are, respectively, proposed. The trade-off between the information and energy transmission is studied for the point-to-point single-input singleoutput (SISO) systems with a PS receiver in [4], which is extended to the point-to-point multiple-input single-output (MISO) systems with a TS receiver in [5]. The TS and PS ratios are optimized to maximize the weighted sum rate of all receivers for the multiuser SISO orthogonal frequency-division multiplexing (OFDM) systems in [7]. Aiming at the minimization for the transmission power, the power allocation problem for Wireless Communications and Mobile Computing the multiuser MISO downlink system is studied, and the optimal PS ratio is obtained in [8]

Methods

Results

Conclusion