Method with strong anti-multi-path capability for processing moveable underwater sound communication signal

Abstract

The invention relates to a method with strong anti-multi-path capability for processing moveable underwater sound communication signals, including two parts, namely a transmitter processing method and a receiver processing method, wherein the transmitter processing method includes the operations of error correction of coding, data packing, digital interpolation, base band shaping wave filtering, upper modified frequency modulation, and the like; and the receiver processing method includes the operations of digital wave filtering, frame synchronous judgment, preliminary compensation of Dopplerfrequency shift, lower modified frequency modulation, bit synchronous judgment, fine compensation of Doppler frequency shift, digital equalization, error correction of decoding, etc. The invention carries out the intercrossing treatment on technologies of synchronous judgment, compensation of Doppler frequency shift, compensation of multi-path effect, and the like, and guarantees that under the environment of strong Doppler frequency shift, the system can realize the accurate synchronism of signals and carries out real-time estimation and compensation on the effect of strong Doppler frequencyshift; and the adopted blind equalization method can carry out effective tracking compensation on the time varying multi-path effect of an underwater sound signal channel, thereby greatly increasing the integral stability and the bit error rate performance of an underwater sound communication system and enduing the system with the capability of reliable communication during movement.

Description

technical field [0001] The invention belongs to the field of underwater acoustic communication, in particular to a mobile underwater acoustic communication signal processing method with strong anti-multipath capability. Background technique [0002] Underwater acoustic communication is a technical means of underwater data transmission by means of sound waves. Compared with radio communication and wired communication, underwater acoustic communication is a more complex communication method. This complexity is caused by some inherent characteristics of underwater acoustic channels. Determined by characteristics: 1) When sound waves propagate in water, interface reflection and sound ray bending will occur, causing multi-path effects and serious inter-symbol interference; 2) Due to the slow propagation speed of sound waves in sea water (about 1500 m / s ), the strong Doppler frequency shift effect caused by the relative movement of the receiving and transmitting parties will serio...

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Problems solved by technology

[0004] At present, the methods for synchronizing underwater acoustic communication are as follows: 1) Using linear frequency modulation (LFM) or m-sequence as the synchronous head, and performing related processing on it when receiving, so as to extract the pulse arrival time and complete the synchronization. This method is simple in calculation, but It is only applicable to low Doppler frequency shift occasions; 2) The LFM signal is used to complete the synchronization by using the characteristic that the LFM signal behaves as an impulse function in an appropriate fractional Fourier transform domain. This method can be used in strong Doppler frequency shift occasions, but A large number of calculations are required, which brings difficulties to the implementation

[0005] At present, the methods for compensating the Doppler frequency shift effect of the underwater acoustic channel are: 1) using the digital phase-locked loop mechanism to compensate the phase deviation caused by the Doppler frequency shift, but this method is also only applicable to the Doppler frequency 2) Use the sampling frequency test method to collect signals according to different sampling frequencies, perform demodulation and decoding processing respectively, and select the optimal result from them. This method will increase the receiver's software and hardware. Complexity, but also less precision

[0006] At present, the methods for compensating the multipath effect of the underwater acoustic channel are: 1) increasing the duration of the symbol to reduce the intersymbol interference, but this will bring about a decline in the communication rate; 2) using spread spectrum and frequency hopping communication technology, this It will occupy a large amount of frequency band resources, and it will also cause a decrease in the transmission rate; 3) Use an adaptive equalization method with a training sequence to compensate the frequency selective fading caused by the multipath effect of the underwater acoustic channel. This method will not Affects the transmission rate of the signal, but because a certain number of training sequences must be sent before the effective sequence is transmitted, it will cause a decrease in the real-time performance of the communication system

[0007] It can be seen from the above that the existing underwater acoustic communication signal processing methods are generally only suitable for low Doppler frequency shift situations. For mobile underwater acoustic communication environments with strong Doppler frequency shift effects, low synchronization accuracy, difficult carrier tracking, and Equilibrium is difficult to converge and other problems, and at the same time it will cause a substantial increase in the amount of calculation, which brings difficulties to the implementation

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