TDOA-based passive localization of standard WiFi devices

Indoor location-based service has widespread applications. With the ubiquitous deployment of WiFi systems, it is of significant interest to provide location-based service using standard WiFi devices. Most of the existing WiFi-based localization techniques are based on Received Signal Strength (RSS) measurements. As the bandwidth of WiFi systems increases, it is possible to achieve accurate timing-based positioning. This work presents a WiFi-based positioning system that has been developed at CSIRO as a research platform, where target devices are located using passive sniffers that measure the Time Difference of Arrival (TDOA) of the packets transmitted by the target devices. This work describes the architecture, hardware, and algorithms of the system, including the techniques used for clock synchronizing and system calibration. It is shown experimentally that the positioning error is 23 cm in open spaces and 1.5 m in an indoor office environment for a 80MHz WiFi system. The system can be used to track standard WiFi devices passively without interfering with the existing WiFi infrastructure, and is ideal for security applications.