Research On Signal Detection And Synchronization Technology With Low Computatiopal Complexity In Underwater Acoustic Communication

Underwater acoustic communication is an important part of the marine resource exploration.For the communication nodes that working in underwater for a long time,the signal detection and timing synchronization are the key technologies to reliable underwater acoustic communication.The underwater acoustic communication has many specific characteristics,such as serious multipath effect and Doppler effect,low SNR,severely limited bandwidth,and so on.Therefore,it is of great application value to study the reliable signal detection and timing synchronization technology in the underwater acoustic communications.For the problem of limited computational performance and power supply of underwater acoustic communication nodes,this paper proposes an energy quotient signal detection algorithm based on multi-tone(MT)signal.The proposed algorithm combines the advantages of simple implementation of energy detection and high reliability of frequency detection,and realizes the requirement of signal detection under low computational complexity by two steps of sliding window energy quotient detection and frequency detection confirmation.Aiming at the problem of poor adaptability of traditional autocorrelation detection algorithm under the Doppler effect,this paper presents an improved autocorrelation signal detection algorithm based on repeated M sequence.By optimizing the block repetition structure to the symbol repetition structure,the improved autocorrelation detection algorithm has reliable detection performance under Doppler effect and low SNR environment.Considering the Doppler effect caused by node movement,focusing on the long preamble of the joint estimation algorithm,the paper propose a joint estimation algorithm of Doppler factor and timing synchronization which is based on Hyperbolic Frequency Modulation(HFM)signal.Based on the Doppler invariance and good correlation performance of HFM signal,the joint estimation algorithm superimposes the HFM signals in the time domain with opposite frequency slopes,by utilizing the related properties of Doppler factor and the peak offset of correlation results in the ambiguity function of HFM signal,the algorithm can obtain a more accurate timing synchronization position while realizing the Doppler factor estimation.Theoretical analysis and simulation results show that compared with the traditional Doppler estimation and timing synchronization algorithm,the joint estimation algorithm has a shorter preamble and can estimate the Doppler factor while obtaining the timing synchronization position,it can also support the real time processing.Finally,the paper carries out a sea experiment for the proposed MT signal-based detection algorithm,improved autocorrelation signal detection algorithm and HFM signal-based joint estimation algorithm of Doppler factor estimation and timing synchronization.The experiment results show that the proposed algorithm based on MT signal has good detection performance under suitable SNR conditions,but the performance is lower under low SNR conditions.The improved autocorrelation signal detection algorithm can achieve reliable signal arrival detection performance by transmitting longer wake-up signals at low SNR conditions.The computational overhead of the two detection algorithms can meet the real-time detection requirements of the duty circuits,and has good anti-interference ability for impulsive noise.The joint estimation experiment based on HFM signal shows that in the Doppler environment,the Doppler spread factor can be estimated accurately by using the superimposed HFM signal,and the corrected precise timing synchronization position can significantly reduce the demodulation error rate.