RIS-Enabled Localization Continuity Under Near-Field Conditions

Reconfigurable intelligent surfaces (RISs) have the potential to enable user localization in scenarios where traditional approaches fail. Building on prior work in single-antenna RIS-enabled localization, we investigate the potential to exploit wavefront curvature in geometric near-field conditions. Via a Fisher information analysis, we demonstrate that while near-field improves localization accuracy mostly at short distances when the line-of-sight (LoS) path is present, it could still provide reasonable performance when this path is blocked by relying on a single RIS reflection. After deriving and illustrating the corresponding position error bounds as a function of key operating parameters, we discuss practical system approaches that could enable better LoS-to-NLoS positioning continuity in harsh environments.