Doppler compensation method for synthetic aperture underwater acoustic communication and system

Abstract

The invention provides a Doppler compensation method for synthetic aperture underwater acoustic communication and a system. With the method, a receiving end can accurately recover baseband signals sent in a diversity mode by a sending end. The method comprises steps: 101) frame synchronization detection is carried out and each frame length is obtained according to the frame synchronization detection; 102) a Doppler factor of each frame is estimated according to each frame length; 103) resampling is carried out on received signals according to the estimated value of the Doppler factor so as to finish coarse compensation of the Doppler effect; and 104) coherent superposition is carried out on signals of each diversity branch after compensation, despreading and demodulation are carried out, and the baseband signals sent by the sending end are recovered. Fine compensation is further carried out on signals after coarse compensation between the step 103 and the step 104. According to the method provided by the invention, the Doppler effect generated due to relative motion of receiving and sending nodes can be effectively resisted, coherent superposition of signals sent by each virtual subarray can be realized, gain loss of synthetic aperture processing space can be reduced and the quality of underwater acoustic communication can be improved.

Description

Technical field: [0001] The invention belongs to the field of underwater acoustic communication, and in particular relates to a Doppler compensation method and system for synthetic aperture underwater acoustic communication. Background technique [0002] The concept of "synthetic aperture" originated from radar, and its basic principle is to use the relative motion of radar and target to obtain high spatial resolution. Foreign scholars have applied the "synthetic aperture" technology to underwater acoustic communication, and realized the combination with the PSK communication system and the multi-carrier system, and the experiments have proved that they have achieved good results. Here, the synthetic aperture technology is not used to increase the aperture size, but to achieve spatial diversity, and this communication method is called synthetic aperture communication (Synthetic Aperture Communication, SAC). In underwater acoustic synthetic aperture communication, a virtual ...

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Problems solved by technology

[0004] H.C.Song et al. used the method of DFPLL phase tracking to realize the rough estimation of Doppler, but this method is only suitable for the case where the moving speed of the carrier is small

Yuan Zhaokai and others proposed to use chirp Z transform to estimate the spectrum of the training sequence. However, due to the high frequency resolution of the pseudo-random sequence, it means that the detection of the correlation peak cannot be realized under the Doppler condition.

In radio spread spectrum communication, PLL is usually used to track frequency and phase. However, the convergence of PLL needs to go through dozens or even hundreds of symbols, which cannot be directly applied to underwater acoustic communication with low code rate.

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