Fast and accurate synchronization method for spread spectrum underwater acoustic communication

Abstract

The invention relates to the field of underwater acoustic communication, particularly to a fast and accurate synchronization method for spread spectrum underwater acoustic communication. The method adopts an m sequence cyclically extended as a frame header, a receiving end uses an m-sequence thumbtack-shaped time-frequency blur characteristic and adopts the fast Walsh transform processing to successively perform frequency deviation coarse and fine search and estimate the initial frequency deviation value of a frame header signal, and a sliding correlation method is used to estimate the starting moment of the frame header signal, so as to complete frame synchronization. A time and frequency synchronization tracking loop is designed by adopting fast Walsh transform processing to further complete time and frequency tracking on each spread spectrum symbol in a frame body. The method has the advantages of overcoming the defect that the conventional method needs to store a plurality of PN sequence versions of different frequency offset, thereby occupying a small amount of storage, and using the FWT processing to reduce the amount of calculation to a large extent, and the composite sequence generated by the m sequence as a spread spectrum sequence; therefore, the method is suitable for spread spectrum underwater acoustic communication of M-ary and PPM hybrid modulation, and has good real-time performance and practicality.

Description

technical field [0001] The invention relates to the technical field of underwater acoustic communication, in particular to a synchronization method for frequency spread underwater acoustic communication. Background technique [0002] Spread spectrum technology has spread spectrum gain, has good anti-noise and anti-multipath interference capabilities, and can communicate under complex multipath and low / negative signal-to-noise ratio conditions, and is widely used in the field of underwater acoustic communication. In recent years, spread-spectrum underwater acoustic communication has adopted technologies such as M-ary spread-spectrum technology and pulse-shift modulation (PPM) to further increase the communication rate. Communication synchronization is a prerequisite for correct decoding, which includes key links such as frame synchronization, time synchronization and frequency synchronization. The purpose of frame synchronization is to find the starting position and initial ...

AI Technical Summary

Problems solved by technology

However, the time compression and expansion of spread-spectrum underwater acoustic communication accumulate more than 1 / 2 chip time, PPM demodulation errors occur and when the PN sequence is long, it is seriously mismatched with the local reference PN sequence, and the gain of related despreading is reduced. Reduced immunity to noise and multipath interference

Therefore, spread spectrum underwater acoustic communication has high requirements for time synchronization and frequency synchronization accuracy, and synchronization processing is more difficult than wireless communication. The synchronization technology of wireless communication is not very suitable for underwater acoustic communication.

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