Standalone Intelligent Reflecting Surface With Automatic Update of Phase-Shift Switching Schedule for Improved Communication and Localization

An intelligent reflecting surface (IRS) allows to control signal propagation and may substantially improve the energy utilization efficiency for sixth-generation mobile communications. We previously proposed a wireless communication system using a standalone IRS that solves two problems: 1) channel estimation overhead for the reflective elements and 2) shared IRS use by multiple wireless network operators. The standalone IRS sweeps the reflected beam by periodically switching the phase shift to cover a wide area. However, when the user area is limited, signals with a phase shift that is not reflected in the user direction are lost. Hence, we propose a method for the standalone IRS to automatically detect useless phase shifts and update the phase-shift switching schedule according to the communication environment. Furthermore, we propose an indoor localization method that supports the automatic update for potential applications such as smart factories and smart homes, in which both communication and the localization of user equipment are required. Simulation results show that the proposed method improves the communication efficiency and localization accuracy by properly updating the phase-shift switching schedule.

I. Introduction

Intelligent reflecting surfaces (IRSs) and reconfigurable intelligent surfaces are attracting attention for improving the energy efficiency of sixth-generation (6 G) mobile communication systems, which are expected to enable ultrahigh-speed and high-capacity communications [1], [2], [3], [4], [5], [6], [7]. An IRS is a reflector with an array of passive reflective elements. By appropriately adjusting the phase shift of every element, the propagation characteristics from the transmitter to the receiver can be controlled and improved. As a result, the transmission power and frequency bandwidth can be reduced while maintaining the desired throughput. However, to properly adjust the phase shift in each reflective element of an IRS, channel information should be obtained for all the elements, leading to a large channel estimation overhead when the IRS contains several elements [6], [7], [8], [9], [10], [11], [12]. In addition, sharing an IRS among multiple wireless network operators is challenging [7], [13], [14]. An IRS with phase-shift control implemented by a particular wireless network operator may adversely affect the communications with other operators. To prevent this problem, when the phase shift is adjusted for multiple operators, a separate control device is required for handling and coordinating the operators, but this increases the cost of infrastructure installation and operation. We previously proposed a wireless communication system to solve two problems by using a standalone IRS (SA-IRS) that periodically switches phase shifts: 1) channel estimation overhead for the IRS reflective elements and 2) shared use of an IRS by multiple wireless network operators [7]. Specifically, the SA-IRS sweeps the reflected beam by switching the phase shift to cover the entire service area. In addition, timing information of the SA-IRS phase-shift switchover is shared and synchronized within the system, and radio resource allocation is quickly optimized by each operator while saving energy by using quantum computing (QC). The periodic phase-shift switching in SA-IRS can be realized using very simple control, without increasing computational complexity or processing delays. Furthermore, while simultaneous reflection in all directions leads to attenuation of array gain and consequently narrows the coverage range of the IRS, the SA-IRS is capable of covering a wide area by sweeping a high-gain reflection beam.