A novel range ambiguity resolution technique applying pulse-position modulation in time-of-flight ranging applications

Abstract

Time-of-Flight range measurements rely on the unambiguous assignment of each received echo signal to its causative emitted pulse signal. The maximum unambiguous measurement range depends on the signal group velocity in the propagation medium and the source signals' pulse repetition interval. When this range is exceeded an echo signal and its preceding pulse signal are not associated any longer and the result is ambiguous. We introduce a novel, two-stage approach which significantly increases the maximum unambiguous measurement range by applying a specifically coded pulse-position-modulation scheme to the train of emitted pulses in the first step. In the second step the analysis of resulting measurement ranges allows the unambiguous decision for the correct ranges. In this regard we also present a unique feature of a group of digital codes which helps to enhance detection robustness. Results are given on the basis of time-of-flight measurements from scanning LIDAR, where this technique has been implemented for the first time.