RCSIL: RIS-Assisted Cooperative Channel State Information Localization for V2X System

In 6G vehicle to everything (V2X) communications, accurate localization is the foundation of high quality intelligent services to users. However, accurate localization requires a significant amount of information and should overcome the Nonline of Sight (NLoS). In this article, we propose the reconfigurable-intelligent-surface (RIS)-assisted cooperative channel state information localization (RCSIL) system to analyze and optimize the localization accuracy based on effective channel state information (CSI). RIS improves the channel quality by adjusting the phase of the reflection unit, thereby affecting the localization performance. Using RIS as an anchor saves a lot of hardware resources. However, the optimization problem of the RIS phase modulation scheme is a nonconvex nonlinear integer programming which is complex and hard to solve. Thus, we propose an Adagrad-gradient-descent-based phase optimization (AG-PO) algorithm, which computes the optimal phase of each reflecting unit in parallel. AG-PO has low complexity, effectively improves positioning accuracy, and performs fast computing. The simulation results indicate that AG-PO outperforms alternating optimization (AO) and genetic algorithm (GA) with a 44.17% and 44.02% reduction in squared position error bound (SPEB) respectively. Thus, RCSIL can be widely applied in 6G V2X communications systems.

I. Introduction

Reconfigurable intelligent surface (RIS) is considered as an important technology for the 6G development and has received widespread attentions [1], [2]. RIS improves spatial channels by changing the phase and reflectivity of each reflective unit. The spatial channel improvement from RIS reduces losses caused by communication and positioning processes, and increases communication rate and localization accuracy [3]. By dynamically adjusting the reflective properties of a large number of passive reflective units, RIS can optimize beamforming, reduce multipath interference, adapt to highly mobile vehicles, improve energy efficiency, enhance safety, and effectively manage high-density connections. This technology is expected to provide more efficient, reliable, and secure communication connections in urban environments and high-density connection scenarios, promoting the development of the vehicle to everything (V2X) [4], [5], [6], which makes it better suited to future communication requirements.