Abstract
Hyperbolic Frequency Modulation (HFM) signal has certain tolerance to Doppler shift. However, during ranging, the unidirectional modulated HFM signal cannot eliminate the Doppler delay at the output of the matched filtering, and thus there is a ranging error. After the combined positive and negative HFM echo signals are matched and filtered, the Doppler-induced delay is closely related and proportional to the frequency, bandwidth and pulse width of the transmitted signals. By using the combined signals, the ranging error in the ranging of single modulated HFM signal can be eliminated. In this paper, a Speed measurement method of Combined HFM signals (SCH) is proposed, which employs positive and negative frequency modulation signals for speed measurement and ranging. Moreover, the SCH method relaxes the requirements of bandwidth and pulse width, which makes it more suitable for general conditions. Extensive simulation results show that the proposed approach can better estimate the speed and distance of moving targets, and it has reference value for engineering application.
Highlights
S ONAR plays a pivotal role in ocean exploration
As countries continue to increase their investment in submarine noise reduction technology, which has led to the rapid development of noise reduction technology
When the Doppler shift produced by the moving target is too large, the spectrum of the Linear Frequency Modulation (LFM) echo signal will be mismatched with the matched filter, which will lead to the loss of the matching gain and the detection performance decreases
Summary
S ONAR plays a pivotal role in ocean exploration. As countries continue to increase their investment in submarine noise reduction technology, which has led to the rapid development of noise reduction technology. The common speed measurement method for sonar is to use a single frequency signal to measure velocity. The single frequency signal will be filtered out by the underwater acoustic channel, resulting in no echo return, and the speed measurement cannot be achieved. The main contributions of this paper are fourfold: 1) The SCH method makes full use of the Doppler characteristic of the moving target and the time delay relationship of the combined signals. The SCH method overcomes the shortcomings of single frequency signal for speed measurement and has better adaptability to ocean channels. In our previous work [4], we propose a Joint Linear frequency modulation and Hyperbolic frequency modulation approach for Speed measurement (JLHS), which employs the same frequency band of positive and negative frequency modulation signals (LFM+HFM) for speed measurement and ranging. Since the tolerance of LFM to moving targets is far less than that of HFM, when the target speed is too high, LFM will have no peak output after matched filtering, and JLHS cannot realize ranging and speed measurement
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