Leveraging RIS-Enabled Smart Signal Propagation for Solving Infeasible Localization Problems: Scenarios, Key Research Directions, and Open Challenges

Abstract

Reconfigurable intelligent surfaces (RISs) have tremendous potential for both communication and localization. While communication benefits are now well-understood, the breakthrough nature of the technology may well lie in its capability to provide and support localization capabilities. We present an overview of RIS-enabled localization scenarios, considering various numbers of RISs, single-or multi-antenna base stations, narrowband or wideband transmissions, and near-and farfield operations. Based on this overview, we also highlight key research directions and open challenges specific to RIS-enabled localization and sensing.

Constrained RIS Phase Profile Optimization and Time Sharing for Near-field Localization

“…4a show that Algorithm 2 (GS -in red) alone does not perform well compared to the PEB, especially at short distance, whereas Algorithm 3 (CF Refinement routine -in amber) significantly boosts the estimation performance at short distances, and even touches the PEB curve at short-to-mid ranges. However, as the RIS-UE distance increases, we notice a drop in performance, this is caused by implementing the approximation in (22) whose error increases as the UE moves further from the RIS. For this reason, a Global Refinement (in dashed black) routine has been implemented to enhance estimation mostly at far distances, where the previous algorithms fail.…”

“…For instance, by leveraging the controllable element-wise phases distribution of a reflective RIS, it is possible to enhance localization continuity, accuracy, and reliability, or even simply just to make localization feasible, in restrictive scenarios and challenging environments [21]. RISs can overcome harsh propagation conditions (e.g., non-line-of-sight (NLoS)) or limited deployment settings for which conventional systems based on active base stations (BSs) would fail [21], [22]. More generally, they can contribute to optimizing signal strength and quality to better estimate the location-dependent radio parameters required for localization [23].…”

RIS-Enabled Smart Wireless Environments: Deployment Scenarios, Network Architecture, Bandwidth and Area of Influence

“…In the following, ten generic scenarios where RISs provide performance benefits for localization are presented (refer to the relevant open technical literature for a more comprehensive overview [26], [27], [28], [29], [30]). These scenarios are visualized in Fig.…”

Joint User Localization and Location Calibration of a Hybrid Reconfigurable Intelligent Surface

“…In the first scenario, except for the base station (BS), the RIS acts as anchor with known state, i.e., location and orientation. These kind of systems are known as RIS-aided or RIS-enabled localization [30], and exploit reflected signals from RISs to improve or assist UE localization. In the second scenario, a UE can use an RIS(s) to enable its localization, where the RIS(s)'s state is unknown and needs to be estimated.…”

“…We assume that there are no scatterers in the BS-HRIS link. This holds from the common placement assumption of (H)RISs in strong LOS conditions from the BS, and mainly close to it[2],[3],[30],[47]. We can also envisage scenarios where the BS and the HRIS are elevated while the UE is located close to the ground 4.…”