Distance estimation for hopping-frequency-coding-based continuous wave.

A distance estimation method for hopping-frequency-coding (HFC)-based continuous wave (CW) is proposed herein. It is important to frequently update the distance estimate of a near-field underwater vehicle, robust to the time delay, Doppler effect, and volume reverberation. Frequency hopping ensures a high estimation accuracy of the wideband signal without being influenced by the Doppler effect, and also allows the receiver to update the target information at each frequency-hopping instance. The proposed algorithm, which is the initial algorithm for HFC-based CW, focuses on the update period of the estimates and real-time implementation rather than the optimization of estimation accuracy. To achieve this goal, the proposed method exploits multiple Doppler correlators, a difference moving average filter, and four thresholds. The update period is inversely related to the hopping frequency, which is directly proportional to the Doppler frequency. As the target or transceiver moves at a high speed, the frequency-hopping period can be reduced, and the proposed algorithm can update the target information more frequently. [ABSTRACT FROM AUTHOR]