RIS-Empowered Integrated Location Sensing and Communication with Superimposed Pilots

2025-04-05

IEEE Transactions on Communications

AI Summary

This work addresses joint communication and localization for mobile users (UEs) lacking prior knowledge of channel state information (CSI) and location. Method: We propose a reconfigurable intelligent surface (RIS)-aided integrated sensing and communication (ISAC) architecture. Specifically, we design a superimposed pilot-and-data transmission frame structure and introduce the first RIS-phase-assisted pilot scheme requiring no prior CSI or position information. We derive the Cramér–Rao bound (CRB) for localization error and employ inverse fast Fourier transform (IFFT)-based estimation to achieve low-complexity, high-accuracy positioning. Additionally, we jointly optimize RIS phase shifts to maximize the ergodic sum rate. Contribution/Results: Theoretically, we establish a Fisher information matrix analysis and derive a closed-form lower bound on achievable rate. Algorithmically, IFFT-based estimation attains localization accuracy approaching the CRB. Compared with conventional pilot schemes, our approach significantly improves spectral efficiency and ergodic sum rate while maintaining high localization precision.

Technology Category

• Intelligent Robots: Localization, Mapping, and Navigation
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Local Search

Application Category

• Search and Retrieval-Augmented AI: Personalized, context-aware and across-device search
• Systems and Infrastructure for Web, Mobile and WoT: Location- and context-aware Web and WoT applications and services
• Security and Privacy: Large-scale security measurements

Abstract

In addition to enhancing wireless communication coverage quality, reconfigurable intelligent surface (RIS) technique can also assist in positioning. In this work, we consider RIS-assisted superimposed pilot and data transmission without the assumption availability of prior channel state information and position information of mobile user equipments (UEs). To tackle this challenge, we design a frame structure of transmission protocol composed of several location coherence intervals, each with pure-pilot and data-pilot transmission durations. The former is used to estimate UE locations, while the latter is time-slotted, duration of which does not exceed the channel coherence time, where the data and pilot signals are transmitted simultaneously. We conduct the Fisher Information matrix (FIM) analysis and derive ext {Cram'er-Rao bound} (CRB) for the position estimation error. The inverse fast Fourier transform (IFFT) is adopted to obtain the estimation results of UE positions, which are then exploited for channel estimation. Furthermore, we derive the closed-form lower bound of the ergodic achievable rate of superimposed pilot (SP) transmission, which is used to optimize the phase profile of the RIS to maximize the achievable sum rate using the genetic algorithm. Finally, numerical results validate the accuracy of the UE position estimation using the IFFT algorithm and the superiority of the proposed SP scheme by comparison with the regular pilot scheme.

Problem

• RIS-assisted location sensing without prior channel info
• Optimizing phase profile to maximize achievable sum rate
• Validating position estimation accuracy using IFFT algorithm

Innovation

• RIS-assisted superimposed pilot and data transmission
• IFFT-based UE position estimation
• Genetic algorithm for RIS phase optimization