Doppler measurement and correction method for MFSK underwater acoustic communication

Abstract

The invention relates to the field of acoustic and signal processing, and mainly discloses a Doppler measurement and correction method for MFSK underwater acoustic communication. At a transmitting end, a frequency point falls on a sideband of an encoded signal by mapping two Doppler measurement spectrum lines; a receiving end can obtain a Doppler measurement value with higher resolution by performing Zoom-FFT processing on a compound fundamental frequency signal of the encoded signal; and finally the measurement value is used for performing Doppler correction and the compensation of time synchronization on the compound fundamental frequency signal. A DSP realizes the setting of two-stage ping-pong buffers which store a radiofrequency signal acquired by an AD and a compound fundamental frequency signal of a digital down converter respectively, improve the real-time and reduce the storage capacity. The method has the advantages that: the method overcomes the disadvantages of measuring Doppler by a single-frequency signal in the prior art; the measurement value can be reflected as a true value for each encoded signal; the measurement spectrum lines can be mapped at a frequency band of response difference and do not occupy an actual communication frequency band; and Zoom-FFT technology can improve the resolution of Doppler measurement, has small operation amount, also occupies less storage resources, and is easy to realize the engineering.

Description

Technical field [0001] The invention relates to the field of acoustics and signal processing, and mainly relates to a Doppler measurement and correction method for MFSK underwater acoustic communication. Background technique [0002] Due to the slow propagation speed of sound waves underwater, the Doppler of the underwater acoustic channel is very serious. When there is relative motion at the communication transceiver, it will cause a large Doppler frequency offset and time compression and expansion effects. At the receiving end, if the FFT transformation of the MFSK communication signal is not corrected for the Doppler frequency offset, the result of the FFT transformation will shift on the frequency axis, which will directly affect the judgment of the information and cause a large bit error. At the same time, the time effect of Doppler Severe synchronization mismatch occurs over time, and the later the FFT time interception window of the MFSK signal deviates, the larger th...

AI Technical Summary

Problems solved by technology

At the receiving end, if the FFT transformation of the MFSK communication signal is not corrected for the Doppler frequency offset, the result of the FFT transformation will shift on the frequency axis, which will directly affect the judgment of the information and cause a large bit error. At the same time, the time effect of Doppler Severe synchronization mismatch occurs over time, and the later the MFSK signal, the greater the deviation of the FFT time interception window, causing greater inter-carrier interference ICI

Doppler measurement generally uses a single-frequency signal, and the measurement resolution is inversely proportional to the pulse width of the signal. Therefore, to obtain a higher frequency resolution, it is necessary for the transmitter to transmit a single-frequency signal with a long pulse width, which takes up communication time and reduces data. rate, and when the relative motion of the communication parties changes, using the measured Doppler frequency offset value, only the Doppler of the coded signal following the single-frequency signal can be corrected, and the Doppler correction of the coded signal that is later, Will cause a large error, thereby increasing the bit error

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