基于形态滤波的水声通信信号同步检测方法

针对水声通信过程中拷贝相关同步检测在不同信道环境下相关峰值差距较大,通过单一固定门限同步检测导致信号误检率、漏检率高的问题,设计了一种信号同步检测帧结构,在传统拷贝相关同步检测信号前加入三单音信号,结合形态学滤波技术,提出了一种新的水声通信信号同步检测方法,实现了不同信道环境和通信距离下单一固定门限检测值的水声通信信号同步检测,降低了信号同步检测的误检和漏检概率。 实际海试结果表明：在 5 km,7 km,10 km 不同通信距离和信道环境下该方法均可实现信号同步检测,信号的误检概率和漏检概率均为 0。     

水声学

声学的一个分支。它主要研究声波在水下的辐射、传播和接收,用以解决与水下目标探测和信息传输过程有关的声学问题。水声学的研究领域主要包括：新型水声换能器;水中非线性声学;水声场的时空结构（如信号场的相关、简正波场的分离和应用、数值声场预报和信道匹配等）;水声信号处理技术（如最佳时空处理、水声信号的参量估计等）;海洋中的噪声和混响背景、散射和起伏,目标反射和舰船辐射噪声;海洋媒质的声学特性（如沉积层和海底、海面、内波及湍流的声学特性）等水声学     

基于带乘性噪声模型的水声通信字符估计算法研究

水声信道多途效应明显,而且存在衰落、散射、损耗以及随机时变等特性,使得水声通信系统的接收信号存在严重的码间干扰.利用带乘性噪声系统模型来刻画随机信道,在建模基础上利用最优滤波递推算法实现状态估计.由于状态向量中的第一维与接收信号之间存在一一对应关系,进而可实现水声信号的估计.该算法在最小方差意义下是最优的,能有效克服码间干扰和噪声污染.2种信道的仿真结果表明,在信噪比(SNR)为18db时,误码率(BER)均已经降低到10-4数量级,验证了算法的有效性.     

潜艇声纳系统水声信号模拟

声模仪供训练声纳员使用。在声模仪里水声信号模拟的依据是水声信号检测理论,在对舰船辐射的噪声和背景干扰噪声及潜艇声纳系统检测信号方法分析的基础上,采用电子线路对水声信号进行模拟。     

面向长时水声通信数据采集与评估的浮标设计与实现

复杂海洋环境导致水声信道呈现随机时-空-频变特性,特别是浅海信道受界面、人为干扰的严重影响,对水声通信造成极大困难。近年来人工智能领域机器学习等技术飞速发展,为提高复杂环境下水声通信可靠性提供了新思路。但是,由于水声信道复杂多变、缺乏普适模型,从机器学习角度而言水声通信数据样本严重不足,传统单次、短时水声通信实验采集的数据无法充分表征水声信道空间、时间特性。通过长期部署水声通信及信号采集设备,可望在一定程度上丰富通信数据,为典型海域下人工智能水声通信研究提供数据支持。 设计并实现了一种浅海水声通信浮标,搭载水声通信系统可实现长时浅海水声通信数据采集、性能评估,同时依托北斗系统具备远程状态显示、功能控制功能。厦门港海域实验表明,依托浮标采集的长时水声通信数据可开展水声通信性能评估、信道特性与通信性能关联度分析,为下一步工作打下了良好的基础。     

Kraken声场建模下目标辐射噪声模拟技术研究

水面目标辐射噪声模拟技术是测试被动声呐系统、目标识别定向及水声软对抗的关键技术。通过对辐射噪声信号特性的描述及分析,建立了水面目标频域线谱及连续谱分量的数理仿真模型。针对水声信道影响因素,将Kraken简正波声场模型与信号本身特性有机结合。以1/3倍频程滤波带宽算法为基础,完成了对宽带FIR滤波器组的设计。采用现在应用广泛的GPU(Graphic Processing Unit)并行加速平台,实时实现了目标噪声模拟器整体架构,大大降低了系统硬件资源的消耗。通过对模拟器输出信号进行数理分析,证明了该模拟器能较好地实现水面目标的辐射噪声特性,具备良好的科研应用价值。     

快速衰落信道环境下SRC检测器的性能分析

分段拷贝相关器是高斯白噪声背景下,快速衰落水声信道中,对应最大似然比准则的最佳接收机,其输出服从χ2分布。推导出有信号时接收机输出端的概率密度函数和检测概率的解析表达式,计算机仿真结果验证了所获得结果的正确性。最后通过计算无信号时接收机输出的概率密度函数,在给定虚警概率的情况下,求出了接收机的检测门限。     

多特征联合水声通信信号调制识别方法

为解决水声信道下通信信号识别困难的问题,对水声 CW、LFM、2FSK、4FSK、BPSK、QPSK、DSSS-BPSK 和 OFDM 信号的调制识别技术进行了研究,旨在提出一种适用于这 8 种信号的调制识别方法。通过对信号的时频特征、二次方谱特征及自相关特征进行分析,并利用基于迁移学习的 ResNet 网络和线性支持向量机进行分类,最终得到了一种多特征联合水声通信信号调制识别方法。仿真表明:在千岛湖多径信道下,信噪比大于 9 dB 时,所研究 8 种信号的识别率均在 99%以上 ;最后,通过海试进一步验证了该方法的可行性,海试数据识别率均在 93%以上。仿真及海试验证的结果表明,所提的方法是适用于水声信道的     

海洋信道多途干扰下提高信息传输可靠度的一种编码方法

水声数据在海洋信道传输过程中．除受到海洋噪声干扰外还存在由于信道界面反射引起的多途干扰。多途干扰的性质不同于海洋噪声及其它类型噪声．在抗干扰理论中所归纳的几种抗干扰方法均不适用本文提出一种编码方法．它使多途干扰信号在某一特定时刻以相同相位同时抵达接收点．由于信号的相互迭加作用使信号幅度增大．有效地提高海洋信道中数据传输的可靠性。     

基于声学宽带扩频信号的抗多径测距技术研究

为研究宽带扩频信号在复杂水声信道下的测距精度,提高水声定位系统的抗多径性能,以BELLHOP模型的多径干扰冲激响应作为水声信道环境基础,通过构造不同传播距离、海洋环境特征的多径水声信道,对宽带扩频编码进行同步相关测距仿真;提出一种基于宽带扩频信号载波域同步的抗多径测距方法,利用载波携带的宽带特征信息进行相关同步以提高理论测距精度。实验结果表明：在有直达声且不考虑声线弯曲条件下,浅海多径信道条件测距精度可达厘米级,中深水信道维持分米级测距精度,较基带同步方法的抗干扰性能有所提升,基于宽带扩频信号载波域同步的抗多径测距方法,能够为声学定位系统的高性能测距技术提供理论依据。     

浅海声信道文本信息传输研究

论文首先介绍浅海声信道声传输的基本特性,指出在此类信道中进行多媒体信息传输的特殊困难.随后论述了文本信息传输所具有的抗噪声、抗起伏等优良性能,较能适应于水声信道的复杂性和多变性,但属于较高速率的文本信息传输,多途干扰仍然是文本信息正确检测的根本障碍.文中分析了频率跳变技术克服时域扩散较短的浅海多途的可行性和需解决的关键技术.海上获得的初步实验结果说明了文本信息传输所具有的优越性,值得今后继续深入的研究.     

基于小型三维阵列的瞬态声源快速被动定位方法

重物在落水和着底过程中都会产生瞬态声信号,这类信号可被运用于浅水区域水下目标定位。 针对浅水区域目标定位的问题,提出了一种基于小型立体五元基阵的瞬态声源快速被动定位算法。 在分析重物落水信号特征的基础上,选取合适的广义互相关加权函数求得传声器之间的声程差,运用快速最小二乘搜索算法进行声源定位。 结果表明:运用 5 传声器阵列可以同时兼顾定位精度和鲁棒性,且满足实时性要求,该方法可运用于浅水区域瞬态声源定位等领域。     

水声宽带信号波形预报技术研究

为了实现远程水下目标微弱信号检测,掌握远程传输后信号波形的特征,水声宽带信号波形预报技术是研究水下信号精细化特征研究的重要突破口之一.针对宽带信号,采用波束位移射线简正波(BDRM)频域合成波形预报算法和 BELLHOP 射线时域波形预报算法,获得宽带信号远程波形预报模型,并在浅海负跃层和深海声道两种典型海洋环境下,利用上述两种宽带波形预报算法,仿真计算了宽带信号远程波形,比较了两种波形预报算法精度.结果表明,在一定条件下,两种模型具有同等计算精度,可满足不同条件下的信号波形预报需求.     

Performance analysis of digital acoustic communication in a shallowwater channel

The major obstacle to underwater acoustic communication is the interference of multi-path signals due to surface and bottom reflections. High speed acoustic transmission over a shallow water channel characterized by small grazing angles presents formidable difficulties. The reflection losses associated with such small angles are low, causing large amplitudes in multi-path signals. In this paper we propose a simple but effective model for multi-path interference, which is then used to assess the performance of a digital communication system operating in a shallow water channel. The results indicate that transmission rates in excess of 8 kbits/s are possible over a distance of 13 km and channel depth of only 20 meters. Such a system offers improved performance in applications such as data collection from underwater sensors     

BDRM理论在双轴海洋声道中的应用

由于表面声道与深海声道间的耦合效应,声波在双轴海洋声道中的传播比较复杂,因此求解双轴海洋声道中的声场就比较困难。在 WKBZ 本征函数的基础上,推导出了参考界面相位修正的一致表达式,并将浅海声传播的波束位移射线简正波(BDRM)理论应用于计算双轴海洋声道中的声场,进行了数值模拟并与传统简正波方法进行比较,结果表明应用 BDRM 理论计算的传播损失具有很高的精度和速度,可以对双轴海洋声道内声传播问题进行分析和预报。     

Recent advances in high-speed underwater acoustic communications

In recent years, underwater acoustic (UWA) communications have received much attention as their applications have begun to shift from military toward commercial. Digital communications through UWA channels differ substantially from those in other media, such as radio channels, due to severe signal degradations caused by multipath propagation and high temporal and spatial variability of the channel conditions. The design of underwater acoustic communication systems has until recently relied on the use of noncoherent modulation techniques. However, to achieve high data rates on the severely band-limited UWA channels, bandwidth-efficient modulation techniques must be considered, together with array processing for exploitation of spatial multipath diversity. The new generation of underwater communication systems, employing phase-coherent modulation techniques, has a potential of achieving at least an order of magnitude increase in data throughput. The emerging communication scenario in which the modern underwater acoustic systems mill operate is that of an underwater network consisting of stationary and mobile nodes. Current research focuses on the development of efficient signal processing algorithms, multiuser communications in the presence of interference, and design of efficient modulation and coding schemes. This paper presents a review of recent results and research problems in high-speed underwater acoustic communications, focusing on the bandwidth-efficient phase-coherent methods. Experimental results are included to illustrate the state-of-the-art coherent detection of digital signals transmitted at 30 and 40 kb/s through a rapidly varying one-mile shallow water channel     

基于Visual C和PC的软件水声调制解调系统

介绍了一种DS/DBPSK调制解调技术方案,该方案采用了具有较强抗干扰、抗衰落和抗多径性能的扩频技术,并结合与信道适应性较好、不需载波恢复的差分相位调制技术,对浅海水声信道造成的干扰进行抑制.在此方法上,基于Visual C(VC)及PC平台设计了一个通用性好的软件水声调制解调系统,利用双缓冲邋和多线程技术机制实现算法实时处理,同时可通过串口通信提供上层应用接口.实验系统验证了扩频和差分调制技术在浅海水声通信中的性能,为水声组网提供了底层支持.海试实验结果表明了系统的有效性.     

Spatial diversity processing for underwater acoustic telemetry

A large increase in the reliability of shipboard or stationary underwater acoustic telemetry systems is achievable by using spatially distributed receivers with aperture sizes from 0.35 to 20 m. Output from each receiver is assigned a quality measure based on the estimated error rate, and the data, weighted by the quality measure, are combined and decoded. The quality measure is derived from a Viterbi error-correction decoder operating on each receiver and is shown to perform reliability in a variety of non-Gaussian noise and jamming environments and reduce to the traditional optimal diversity system in a Gaussian environment. The dynamics of the quality estimator allow operation in the presence of high-power impulsive interference by exploiting the signal and noise differential travel times to individual sensors. The spatial coherence structure of the shallow water acoustic channel shows relatively low signal coherence at separations as short as 0.35 m. Increasing receiver spacing beyond 5 m offers additional benefits in the presence of impulsive noise and larger-scale inhomogeneities in the acoustic field. A number of data transmission experiments were carried out to demonstrate system performance in realistic underwater environments     

A New Method for Matched Field Localization Based on Two-Hydrophone

The conventional matched field processing (MFP) uses large vertical arrays to locate an underwater acoustic target. However, the use of large vertical arrays increases equipment and computational cost, and causes some problems such as element failures, and array tilting to degrade the localization performance. In this paper, the matched field localization method using two-hydrophone is proposed for underwater acoustic pulse signals with an unknown emitted signal waveform. Using the received signal of hydrophones and the ocean channel pulse response which can be calculated from an acoustic propagation model, the spectral matrix of the emitted signal for different source locations can be estimated by employing the method of frequency domain least squares. The resulting spectral matrix of the emitted signal for every grid region is then multiplied by the ocean channel frequency response matrix to generate the spectral matrix of replica signal. Finally, the matched field localization using two-hydrophone for underwater acoustic pulse signals of an unknown emitted signal waveform can be estimated by comparing the difference between the spectral matrixes of the received signal and the replica signal. The simulated results from a shallow water environment for broadband signals demonstrate the significant localization performance of the proposed method. In addition, the localization accuracy in five different cases are analyzed by the simulation trial, and the results show that the proposed method has a sharp peak and low sidelobes, overcoming the problem of high sidelobes in the conventional MFP due to lack of the number of elements.     

Analysis of EMD algorithm for identification and extraction of an acoustic signal in underwater channel against wind driven ambient noise

Sonar generated acoustic signals transmitted in underwater channel for distant communications are affected by numerous factors like ambient noise, making them nonlinear and non-stationary in nature. In recent years, the application of Empirical Mode Decomposition （EMD） technique to analyze nonlinear and non-stationary signals has gained much attention. It is an empirical approach to decompose a signal into a set of oscillatory modes known as intrinsic mode functions （IMFs）. In general, Hilbert transform is used in EMD for the identification of oscillatory signals. In this paper anew EMD algorithm is proposed using FFT to identify and extract the acoustic signals available in the underwater channel that are corrupted due to various ambient noises over a range of 100 Hz to 10 kHz in a shallow water region.Data for analysis are collected at a depth of 5 m and 10 m offshore Chennai at the Bay of Bengal. The algorithm is validated for different sets of known and unknown reference signals. It is observed that the proposed EMD algorithmidentifies and extracts the reference signals against various ambient noises. Significant SNR improvement is alsoachieved for underwater acoustic signals.