Ultra-Wideband TOA Estimation in the Presence of Clock Frequency Offset

The paper is concerned with the impact of clock frequency offsets on the accuracy of ranging systems based on time of arrival (TOA) measurements. It is shown that large TOA errors are incurred if the transmitter and receiver clocks are mistuned by more than just one part per million (ppm). This represents a serious obstacle to the use of commercial low-cost quartz oscillators, as they exhibit frequency drifts in the range of ±10 ppm and more. A solution is to estimate first the transmitter clock frequency relative to the receiver´s and then compensate for the difference by acting on the receiver clock tuning. An algorithm is proposed that estimates the transmitter clock frequency with an accuracy better than 0.1 ppm. Computer simulations indicate that its use in ranging systems makes TOA measurements as good as those obtained with perfectly synchronous clocks.