Frequency Shift Arrival Time Determination of Acoustic Signals

In the demodulation of underwater acoustic signals, timing determination is usually based on the leading edge of a pulse, and is therefore subject to errors that are functions of pulse rise time and signal level. This paper describes a system using a phase-locked loop demodulator to determine the time of arrival of a frequency-shifted pulse. In this system, timing is shown to be essentially independent of signal strength, and timing jitter is shown to be low.