Fiber-Topology-Assisted Indoor Positioning Under UWB Degradation with Fixed-Lag Factor Graphs

Abstract

Ultra-wideband (UWB) provides absolute spatial constraints for indoor positioning, but these constraints become insufficient when multiple radio links are blocked or unavailable. A calibrated sensing fiber, in contrast, provides a fixed spatial topology that can be activated by distributed acoustic sensing (DAS) events independently of radio propagation. Motivated by this complementarity, we present FTALoc-FGO, a topology-aware fixed-lag factor-graph framework for fiber-assisted localization under UWB degradation. Along-fiber DAS events are mapped through the calibrated topology into anisotropic spatial observations, where a single fiber layer provides a directional constraint and two orthogonal layers provide complementary two-dimensional information. Fisher-information analysis characterizes this topology-dependent information and motivates the directional and joint fiber factors used in the fixed-lag graph. Experiments combining measured DAS events with simulated UWB ranges under controlled degradation evaluate the method over 30 paired realizations. Under complete UWB loss, FTALoc-FGO reduces the causal outage RMSE by 32.6\% and 66.4\% for single- and dual-layer routes, respectively, relative to robust UWB-only FGO. These results demonstrate that calibrated fiber topology can provide complementary spatial support when radio-based observations become insufficient.