Impact of clock drift on WiFi round-trip-time ranging and positioning

Indoor high-precision positioning is currently one of the most interesting topics in the location-tracking and positioning research area. Although the WiFi round-trip-time (RTT) provides a promising ranging and positioning method, it faces two issues that need to be addressed. One is the ranging error drift, and the other is the ranging information loss. Existing research has mainly focused on the ranging error, and several solutions have been proposed. However, these solutions are mostly applied to the data level, and the cause of phase distortion error has not been found. The loss of ranging information has been simply attributed to the poor external environment. In this work, the impact of clock drift on WiFi RTT positioning is investigated and considered the root cause of the abovementioned issues. On this basis, a theory of the clock drift model is established and experimentally verified. This model can effectively explain the mechanism of the ranging error drift and the ranging information loss. Furthermore, the impact of the clock drift on missing positioning observations is investigated in three actual applicational situations, including the sampling rate, multipath effect, and power-saving mode. Therefore, the proposed model is important for improving the accuracy and reliability of WiFi RTT-based positioning because it provides the basis for solving subsequent problems. This model provides a theory to capture the moment when the communication status changes accurately. Furthermore, the ranging error drift can be corrected to obtain high-precision positioning results.