Joint Localization and Communication Study for Intelligent Reflecting Surface Aided Wireless Communication System

The intelligent reflecting surface (IRS) is promising in assisting user localization and wireless communication in the future wireless networks. In this paper, a novel IRS-aided joint localization and communication (L&C) scheme is designed in a millimeter-wave transmission system. For the proposed scheme, the user position/orientation estimation error bound (POEB) and the effective achievable data rate (EADR) are derived in closed-form as L&C performance metrics, which reveal the inherent trade-off between L&C capabilities. To achieve the joint optimal point of the POEB and EADR in consideration of the localization errors, a worst-case robust beamforming and time allocation optimization problem is formulated. To solve the original non-convex problem, a novel joint optimization approach is developed. Specifically, from an equivalent minimax problem, the local optimal solutions of the transceiver beamformers, the IRS phase-shift matrix, and the time allocation ratio between user localization stage (ULS) and effective data transmission stage (EDTS), are obtained in closed-form with respect to the localization errors. Then, the worst-case localization error is iteratively found by a dedicated majorize-minimization (MM) based algorithm. Subsequently, potential extensions to general wireless channels and discrete phase-shift models are discussed in detail. Finally, simulations are carried out to show the optimization results and the L&C performance trade-off. In comparison with the conventional non-robust method, the proposed approach is validated to be robust against the user localization uncertainty.

I. Introduction

The fifth-generation (5G) mobile communication network has been standardized and commercially deployed in part since the first quarter of 2020, while the researches on the sixth-generation (6G) mobile communication have already begun to advance [1], [2], [3]. To fulfil the demands of Gbps-level of achievable data rate, high spectral efficiency, mass connectivity and ultra reliability in 6G [3], various key enabling technologies including the millimeter-wave (mmWave), massive multiple-input-multiple-output (MIMO) and ultra-dense network (UDN), can be incorporated to boost the communication capability. In addition, the mmWave and massive MIMO can also be combined to achieve accurate localization for user equipments (UEs) based on the channel parameters (e.g. angle of arrival/departure (AOA/AOD), time delay, etc.) [4], [5], owing to the “quasi-optical” propagation property of the mmWave signals [6] and the compact directional and steerable large antenna arrays of the massive MIMO [7]. While these technologies possess the above advantages, they are still unable to address several critical challenging issues when used in practice. First, the mmWave is susceptible to blockage and suffers from serious propagation loss due to its high frequency. Second, the massive MIMO and UDN consist of large-scale antenna arrays and serried base stations (BSs), resulting in high hardware cost and energy consumption. In view of these problems, the future 6G will focus on the exploration of novel communication paradigms on the foundation of the current 5G.