Joint Resource Optimization for Cognitive Sensor Networks with SWIPT-Enabled Relay.

Weidang Lu,Tian Nan,Xin Liu,Yuanrong Lin,Hong Peng

doi:10.3390/s17092093

Abstract

Energy-constrained wireless networks, such as wireless sensor networks (WSNs), are usually powered by fixed energy supplies (e.g., batteries), which limits the operation time of networks. Simultaneous wireless information and power transfer (SWIPT) is a promising technique to prolong the lifetime of energy-constrained wireless networks. This paper investigates the performance of an underlay cognitive sensor network (CSN) with SWIPT-enabled relay node. In the CSN, the amplify-and-forward (AF) relay sensor node harvests energy from the ambient radio-frequency (RF) signals using power splitting-based relaying (PSR) protocol. Then, it helps forward the signal of source sensor node (SSN) to the destination sensor node (DSN) by using the harvested energy. We study the joint resource optimization including the transmit power and power splitting ratio to maximize CSN’s achievable rate with the constraint that the interference caused by the CSN to the primary users (PUs) is within the permissible threshold. Simulation results show that the performance of our proposed joint resource optimization can be significantly improved.

Highlights

Cognitive radio (CR) is a promising technology that aims to solve the problem of spectrum scarcity.For the underlay spectrum sharing mode, the secondary users (SUs) can share the licensed spectrum on condition that the interference to primary users (PUs) caused by the transmission of the SUs is within the permissible threshold [1]
We assume that the path loss exponent m = 3, the energy harvesting efficiency η = 0.8, the distance dSSN,relay sensor node (RSN) + dRSN,destination sensor node (DSN) = 2, and dPT,RSN = dPT,DSN = dSSN,primary receiver (PR) =
Moves closer to sensor node (SSN), which is due to the fact that when RSN is located closer to SSN, it can harvest more power in the first slot to help forward SSN’s signal to DSN in the second slot

Summary

Introduction

Cognitive radio (CR) is a promising technology that aims to solve the problem of spectrum scarcity. The approximate expressions for throughput and ergodic sum-rate of AF cognitive network with energy harvesting relay were derived in [18], while the interference caused by the relay node was ignored. We obtain the transmission rate expression of AF CSNs with energy harvesting relay by considering the interference caused by the relay sensor node. We derive the transmission rate expression of AF CSNs with energy harvesting relay by considering the interference caused by the relay sensor node, which was ignored in [18]. An algorithm is proposed to obtain the closed-form optimal value of transmit power and power splitting ratio—unlike [17], in which the optimal energy harvesting duration was derived through the simulation.

System Model

Problem Formulation

Joint Optimization of Transmit Power and Power Allocation Ratio

Simulation Results and Discussion

Conclusions