Wi-PRO: Accurate Indoor PNT using FTM with Multipath Suppression

Accurate indoor localization remains a significant challenge as GPS signals fail to penetrate indoor environments. While the IEEE 802.11mc standard introduced Fine-Timing Measurement (FTM) to enable Wi-Fi-based ranging, commercial off-the-shelf (COTS) implementations of FTM often suffer from ranging errors exceeding several meters due to proprietary hardware limitations and multipath interference. Existing solutions typically rely on crude statistical corrections to standardized 802.11mc ranging measurements using channel state information (CSI). In this paper, we propose Wi-PRO (Wireless Positioning using Range Offsets), a system designed to achieve high-accuracy indoor positioning using distributed, low-cost ESP32 nodes. Unlike previous statistical correction methods, Wi-PRO addresses the root causes of FTM inaccuracies in single-antenna systems. We identify and mitigate two primary sources of error: nonlinear phase jumps across channel-bonded CSI measurements and incorrect start-time detection in hardware timestamping. By developing algorithms that calibrate low-quality CSI and compensate for multipath profiles, Wi-PRO significantly refines Time-of-Arrival (ToF) estimates. Experimental results demonstrate that our approach corrects FTM ranging offsets to provide meter-level localization accuracy, offering a scalable and cost-effective PNT solution for the modern IoT ecosystem. We release Wi-PRO's codebase and dataset to the open-source community¹ https://github.com/ucsdwcsng/wi-pro-esp32-ftm.