WSN06-3: Improving Two-Way Ranging Precision with Phase-offset Measurements

Two-way ranging (TWR) based on time-of-arrival (TOA) provides a viable ranging solution that does not necessitate clock synchronization among the devices in an ad-hoc network. However, the accuracy of TOA-based solutions suffer from the finite sampling clock-frequency resolution. This paper introduces a novel technique of improving the accuracy of TWR using additional phase-offset ranging measurements. These additional ranging measurements are performed at n/N, n = 1, ... , N - 1 clock-period phase-offsets introduced in the device that initiates the ranging measurement. It has been analytically shown that the appropriate use of the differences between the time of arrival (in clock cycles) estimated without and with n/N, n = 1, ... , N - 1 clock-period phase-offset reduces the sampling-clock uncertainty due to the finite resolution of the clock. The improved performance obtained is equivalent to the use of N times higher sampling clock frequency. Our analytical results are further corroborated by simulations.