Joint User Detection and Localization in Near-Field Using Reconfigurable Intelligent Surfaces

This letter studies the problem of detecting active user equipment devices (UEs) and localization in the near field, wherein the base station (BS) is unaware of the number of active (or inactive) UEs and their positions. The system is equipped with multiple reconfigurable intelligent surfaces (RISs), which provide a low-complexity solution for detection and localization with additional degrees of freedom due to the additional inspection points. Specifically, we propose an iterative detection procedure, allowing the BS to assign pilots to detected UEs, and thereby providing a structured channel access. Also, the problem of multiple access interference is explored as a limiting performance factor. The results show that, with a proper configuration of the RISs, the proposed scheme can detect/localize UEs, augmenting benchmark detection schemes to spatially aware UE detection.