A simple rising-edge detector for time-of-arrival estimation

A fast and simple technique for acoustic-pulse timing that is particularly suited for use in reverberant, multipath environments has been developed and implemented as part of an underwater acoustic positioning system. The technique analytically fits the rising edge of the pulse using two threshold levels and the corresponding threshold crossing times to give an asymptotically unbiased estimate of the time of flight. The technique yields a significant improvement in timing accuracy over the standard single-level threshold-crossing scheme, yet involves minimal additional electronic complexity. Selection of the two threshold levels, taking into account the expected variation in received signal levels, and the effects of system SNR on timing accuracy have been investigated.