Intelligent Reflecting Surface Enhanced User Cooperation in Wireless Powered Communication Networks

An intelligent reflecting surface (IRS) comprises a massive number of low-cost passive elements that can be controlled to reflect the incident signals into a structured output pattern. In this letter, we consider IRS-assisted user cooperation in a wireless powered communication network (WPCN), where two users harvest wireless energy and transmit information to a common hybrid access point (HAP). In particular, we exploit the use of IRS to enhance the energy efficiency in the wireless energy transfer (WET) phase and the spectral efficiency in the wireless information transmission (WIT) phase. We derive the maximum common (minimum) throughput performance by jointly optimizing the transmit time and power allocations of the two users and the passive array coefficients on reflecting the wireless energy and information signal. Simulation results show that the use of IRS can effectively improve the throughput performance of cooperative transmission in WPCNs.

I. Introduction

The capacity of current wireless networks needs exponential increase to meet the rapidly growing demands for high-data-rate multimedia access in the fifth-generation (5G) networks. A variety of wireless technologies have been proposed and investigated in the recent years to improve the spectral efficiency, such as millimetre wave (mmWave) and massive multiple-input multiple-output (mMIMO) technologies. However, these advanced technologies also impose high energy consumption and hardware cost, which hurdle their deployment in practical systems [1]. To address this problem, recently there have been extensive research works on wireless powered communication networks (WPCNs), which use dedicated wireless energy transferring nodes to power the operation of communication devices [2]–[7]. Compared to its conventional battery-powered counterpart, the WPCN has shown its advantages in lowering the operating cost and improving the robustness of communication service especially in low power applications, such as sensor and Internet of Things (IoT) networks.