无线/水声通信浮标技术研究及其实现

本文研究并设计实现了一种用于浅海水声信道多速率通信的无线/水声通信(racom)浮标,介绍了其水声通信和无线通信技术方案和工程设计与实现。本文设计的浮标综合了水声通信、DSP信号处理和无线电通信等技术,也可以用作水声通信/传感网络中的无线/水声通信(racom)网关节点。海上试验验证了本浮标总体设计方案的可行性。海上试验中,浮标无线通信距离达到15.2 km,误码率不大于10 6;除2 kbps速率外,浮标各种速率的水声通信数据传输误码率都小于1%,最大通信作用距离达到9.6 km;同时,试验也验证了浮标与水下运动平台之间的通信功能。     

水声高速图像传输信号处理方法

研究了水声图像高速传输信号处理方法,它包括两个方面,一方面是水声相干通信信号处理方法,其中:(1)多普勒频移补偿,在数据包的前后两端插入已知线性调频(Chirp)信号,拷贝相关后求互相关,估计相对多普勒平均频移。在自适应判决反馈均衡器中加上自适应相位补偿器,采用快速自优化最小均方(LMS)算法,与其对应的速度容限优于常用的二阶锁相环相位补偿器的。两种补偿方法联合工作时,性能优良。(2)带有分集合并器的自适应判决反馈均衡器的算法是快速自优化的LMS算法,计算量小,性能优良。(3)自适应判决反馈均衡器与Turbo-网格编码调制(TCM)译码器级连、迭代算法。研究了基于软输出维特比(SOVA)方法的新型的比特-符号转换器,用它时误比特率(BER)比常规编码、映射方法的近似小2个数量级。另一方面是抗误码的图像压缩方法。本文基于数字小波变换和定长编码方法,研究了声图像的压缩。它包括:(1)选用CDF9/7小波进行小波变换。(2)对小波系数子带能量进行统计分析,三层小波分解是合适的。(3)对不同能量的子带采用不同的量化步长。(4)采用定长编码算法。结果表明声图像压缩比特率为0.85。当BER小于10~(-3)时,图像质量完好。当BER小于10~(-2)时,图像中出现少量小黑白点。在上述基础上研制了水声通信机,频带为(7.5～12.5)kHz,接收声呐阵为8基元等距线阵,信号为QPSK和8PSK。在中国千岛湖进行了湖试,采用SOVA硬迭代算法,达到了低BER。传输一幅256×256×8的声图需时约7s。传输距离与传输速率之积为55 km kbps。     

正交码元移位键控扩频水声通信

码元移位键控(CSK)作为一种广义的M元扩频技术被广泛应用于水声通信领域来克服扩频增益对通信速率的限制.为了获得更高的通信速率, 减少通道间干扰, 并充分利用 CSK的冗余信息, 本文提出联合利用码元相位信息的正交双通道CSK扩频水声通信技术.首先, 推导了正交CSK每符号积分输出的表达式; 然后, 研究了正交CSK的性能及与传统CSK和双通道CSK对比仿真的误码率; 最后, 通过实验验证了仿真对比的正确性. 实现了正交CSK在10⁴ bits, 4 kHz带宽下580.6 bps通信速率的有效传输. 通过公式推导、 仿真分析和实验研究, 得到正交CSK提供了优良的性能的结论. 关键词： 水声通信 扩频 正交 CSK     

接近非相干水声通信信道容量的信号处理算法

恶劣情况下的非相干水声通信信道模型为随机相位Rayleigh衰落,推导了该模型的信道容量曲线。为实现接近非相干信道容量的可靠通信,提出多进制低密度校验码(LDPC)和恒重码级联码的多进制非相干概率域迭代处理算法。在信道幅度和相位完全未知的情况下,根据矩估计得到信号和噪声频点幅度的统计参量,进而得到恒重码的码字后验概率,再对多进制LDPC码进行因子图迭代译码。仿真证明本算法与现有的最大能量检测非迭代译码算法相比,与信道容量曲线的差距从4.5dB缩小至1.5dB。给出了实际海试湖试通信效果,频段为6~10kHz,数据速率为357bps,海试时近似垂直通信距离为5km,湖试时水平通信距离近3km、多径超过50mS,两种情况下无差错通信的信噪比门限为2dB,验证了本算法的优势。      

水声信号处理领域新进展

本文介绍近30年来水声信号处理领域理论研究的新进展和在声纳设计中的应用。包括水声信号建模、声场匹配、海洋波导和内波现象的探索和研究、声矢量场信息获取和处理,低频水声信道的时/空相关特性,水下目标辐射噪声的不变特征量提取和检测技术,水下语音、图像传输和抗干扰技术。同时概述,声纳设计的前沿领域:大孔径拖曳线列阵声纳、高分辨力合成孔径声纳、深海传呼机等的发展情况。     

一种利用海豚叫声的仿生水声通信方法

针对水下通信隐蔽性的需求, 克服传统固定载波调制方式带来的声源暴露问题, 提出一种基于海豚叫声的仿生伪装水声通信方法, 使通信信号被当作海洋生物噪声排除, 达到隐蔽通信的效果. 研究了海豚叫声信号特点, 利用海豚哨声信号实现同步与识别, 采用差分脉冲位置调制方法, 信息调制在相邻海豚嘀嗒声信号的时间间隔, 采用压缩传感体制下的匹配追踪技术估计信道, 虚拟时反技术实现信道均衡. 湖试结果验证了该方法的有效性和可行性, 接收声信号与发射信号声音上具有很高的相似度, 可以达到伪装隐蔽的效果. 实验中水平距离2 km, 通信速率不小于29 bps时,误码率可以达到10^-4以下. 关键词： 水声通信 仿生 海豚 隐蔽     

水声通信技术综述

受制于严重的衰减,电磁波在水中的传播距离非常有限,因此以声波为载体的水声通信是在水下实现无线信息传输的主要方式。水声通信无论是在军事方面还是在民用方面都有重要的作用,随着人类加快开发海洋的步伐,对水声通信技术的需求也变得越来越迫切。文章对水声通信技术进行了综合介绍。首先介绍了水声通信的概念和意义,着重分析了水声信道的特点以及水声通信面临的困难,然后对目前应用较多的几种典型水声通信技术进行了介绍,最后对水声通信技术的发展方向进行了展望。     

相干水声通信系统中均衡器长度设计方法

基于自适应均衡技术的相干通信被证明是有效的水声通信方式之一。在均衡器设计过程中,确定均衡长度的方法主要是经验确定与搜索算法,前者依赖于特定的环境,后者一般计算量较大。本文提出一种应用于相干水声通信系统的根据信道冲激响应确定均衡长度的设计方法。仿真及试验结果证明了该方法可以有效地提高通信的可靠性。     

水声通信中基于信道辨识的盲turbo均衡方法

水声信道多途效应明显,造成接收信号存在严重的码间干扰(ISI,Intersymbol interference)。基于最小均方误差(MMSE,Minimum mean square error)准则的turbo均衡器级联了均衡和信道译码,能够有效去除ISI,并获得优良的性能。由于水声信道的时变性,传统MMSE-turbo均衡需要周期性的训练序列,以实现连续可靠的通信。训练序列虽然提高了通信的可靠性,但降低了信息的有效传输速率。因此,为提高通信效率,本文提出了一种盲turbo均衡方法,该方法通过引入新的盲信道辨识器来同时获得信道估计响应和已去除部分ISI的初步均衡输出信号,并为turbo均衡提供初始的响应参数和比特软信息。与水声通信中应用较多的盲判决反馈均衡器(DFE,Decision feedback equalizer)相比,海上实验结果证明本文提出的盲turbo均衡方法抗信道多途衰落的能力较强,并且与传统MMSE-turbo均衡相比无需训练序列,因此提高了信息的有效传输速率。     

稀疏信道条件下正交多载波扩频水声通信无导频信道估计算法

提出了一种无导频信道估计算法,该算法首先利用水声信道的稀疏特性对扩频信号进行识别,再利用扩频信号识别结果对水声信道响应进行判决反馈估计,从而实现对稀疏水声信道响应的可靠重建。仿真和湖上试验结果证实:无导频信道估计算法可以在不降低通信质量的前提下,实现对水声通信信号的稳健均衡,提升水声通信速率。      

一种在色噪声环境下的信号检测方法

为了抑制蛟龙号载人潜水器水声通信受母船色噪声干扰的影响,本文提出了一种统计匹配滤波器在色噪声环境下使用的新方法,它通过将接收信号映射到一个生成子空间中进行信号检测,可提高输出水声通信信号的信噪比。受客观条件限制,向阳红09船——蛟龙号载人潜水器的试验母船噪声环境比较恶劣,对水声通信产生了较强的干扰。如何在向阳红09船的这种强、色噪声环境下,提升水声同步信号的检测能力,对提高水声通信的可靠性是非常有帮助的。实际采集试验数据分析结果验证了该检测算法比传统匹配滤波器有更强的信号检测能力。     

Signal processing for high speed underwater acoustic transmission of image

A signal processing method for high-speed underwater acoustic transmission of image is presented. It has two parts. Part 1 introduces signal processing for underwater acoustic coherent communication. Part 1 includes 3 technical points. （1） Doppler shift compensation. Chirp signals are inserted between data packages. A correlation process between two copy correlation functions gives more accurate estimation of the mean Doppler shift. Then it could be compensated by resampling the data. In adaptive decision feedback equalizer （DFE） an adaptive phase compensator with fast self-optimized least mean square （FOLMS） adaptation algorithm is utilized resulting in better motion tolerance than compensators with 2nd order Phase-Lock Loop algorithm. The performance of the combination of mean Doppler shift compensation and adaptive phase compensator is quite good. （2） A diversity combiner （DC） used in advance of equalizer. Both combiner and adaptive DFE are based on FOLMS adaptation algorithm. This results in reduced computation complexity and better performance. （3） Cascaded equalizer and Turbo-Trellis Coded Modulation （TCM） decoder and the iteration algorithm. A new bitsymbol converter based on Soft Output Viterbi Algorithm （SOVA） is studied. Comparing with the traditional decision, coding and mapping algorithm, the new converter can reduce Bit Error Rate（BER） by nearly 2 orders. Part 2 is mainly around a robust image compression algorithm. Based on Discrete wavelet transform and fixed length coding, a robust compression algorithm for acoustic image is studied. The algorithm includes 4 technical points. （1） Utilizes CDF9/7 wavelet bases to transform the images. （2） Analyses the energy distribution of subband coefficients. Suitable transformation layer number is 3. （3） Applies different quantization steps to different subbands in accordance with their energy distribution. （4） Uses fixed length coding to prevent error propagation. The results show the algorithm achieves a balance among image quality, compression rate, and most important, robustness to BER. The compressed bit rate of gray scale acoustic image is 0.85 bit/pixel. Image quality remains good when BER is lower than 10^-3. There are some small dirty points when BER rises to 10^-2. Based on the signal processing techniques above mentioned, an underwater acoustic commumcation system is built. Its operational frequency band is （7.5-12.5） kHz. Its receiving array is an 8 elements uniform linear array. QPSK and 8PSK modulation and iteration algorithm for cascaded equalizer and 1-Turbo-TCM decoder based on hard SOVA are used. The system has been tested in Qiandao Lake. Low BER is achieved in 5.5 km range when data rate is 10 kbps. One gray scale image can be transmitted in 7 s. The product of its communication distance and data rate is 55 km kbps.     

基于扩频码的单载波迭代频域均衡水声通信

单载波时域均衡在长时延扩展水声信道中计算量大,并对接收机参数的选择较为敏感,可靠性低,而正交频分复用信号峰均功率比高、对频率偏移敏感. 针对这些问题,提出基于扩频码的单载波块传输高速率水声通信方法和基于T/4分数间隔迭代频域均衡的接收机算法. 该接收机利用已知扩频码进行信道估计以及对由多普勒偏移引起的旋转相位进行估计,并通过一种低复杂度迭代频域均衡算法改善系统性能. 开展了湖上实验研究,结果表明在浅水1.8 km距离且复杂多径干扰条件下,利用BPSK/QPSK调制可实现10^-2–10^-4的误码率并达到1500–3000 bit/s的有效数据率. 关键词： 水声通信 单载波 频域均衡 迭代处理     

近程高速水声毫米波通信仿真与试验验证*

水声信道的严重双扩特性极大地限制了水声高速通信的稳健性。针对近程高速水声通信技术的需求,该文基于水声毫米波频段,提出了一种基于超奈奎斯特发射技术及高阶调制技术的单载波的水声毫米波通信技术。而超奈奎斯特发射技术以及高阶调制给接收机带来了极大的挑战:一是超奈奎斯特发射技术引入了严重的符号间干扰,二是高阶调制系统的符号检测对信道估计的精度要求很高。针对以上问题,该文提出了一种基于迭代信道估计技术的迭代软反馈DFE接收机技术。仿真实验表明:采用128QAM高阶调制时,在较为严重的多途衰落信道条件下,采用所提出的接收机可以在15 dB时实现无误码传输。信道水池试验证明:当通信带宽为300 kHz,通信符号率为300k符号/秒且采用64QAM调制时,在发射平台慢速运动的条件下可以实现900 kbps的净数据率,其相应的频谱利用率高达6 Bits/s/Hz。     

Overview of channel models for underwater wireless communication networks

Acoustic communication in Underwater Wireless Communication Networks (UWCNs) has several challenges due to the presence of fading, multipath and refractive properties of the sound channel which necessitate the development of precise underwater channel models. Some existing channel models are simplified and do not consider multipath or multipath fading. In this paper, a detailed survey on ray-theory-based multipath Rayleigh underwater channel models for underwater wireless communication is presented and the research challenges for an efficient communication in this environment are outlined. These channel models are valid for shallow or deep water. They are based on acoustic propagation physics which captures different propagation paths of sound in the underwater and consider all the effects of shadow zones, multipath fading, operating frequency, depth and water temperature. The propagation characteristics are shown through mathematical analysis. Transmission losses between transceivers are investigated through simulations. Further simulations are carried out to study the bit error rate effects and the maximum internode distances for different networks and depths considering a 16-QAM modulation scheme with OFDM as the multicarrier transmission technique. The effect of weather season and the variability of ocean environmental factors such as water temperature on the communication performance are also shown. The mathematical analysis and simulations highlight important considerations for the deployment and operation of UWCNs.     

Signal processing for noncoherent underwater acoustic communication approaching channel capacity

Noncoherent underwater acoustic communication channel in adverse conditions is modeled as a phase-random Rayleigh fading channel,and its capacity curve is derived.To approach the channel capacity curve,the concatenated code of the nonbinary LDPC code and the constant weight code is proposed for noncoherent communication which can late be iteratively decoded in the probability domain.Without information of channel amplitude or phase in the receiver,statistic parameters of the respective signal and noise bins were estimated based on the moment estimation method,the posterior probabilities of the constant weight code words were further calculated,and the nonbinary LDPC code was decoded with the nonbinary factor graph algorithm.It is verified by simulations that by utilizing the proposed concatenated code and its processing algorithm,gap to channel capacity curve is reduced by 3 dB when compared to the existing method.Underwater communication experiments were carried out in both deep ocean（vertical communication,5 km）and shallow lake（horizontal communication,near 3 km,delay spread larger than 50 ms）,in which the signal frequency band was 6 kHz to10 kHz,and the data transmission rate Was 357 bps.The proposed scheme can work properly in both experiments with a signal-to-noise ratio threshold of 2 dB.The performance of the proposed algorithm Was well verified by the experiments.     

Time reversal acoustic communication receivers: DSP implementation and fast channel estimation

A communication system is implemented on digital signal processors (DSPs) for the underwater acoustic environment. The implemented receiver uses time reversal multi-channel combining followed by a single-channel decision feedback equalizer. Periodic channel estimation is employed to track the channel fluctuations. These techniques are used to mitigate time-varying inter-symbol interference, which is the main challenge in the underwater acoustic channel at operating frequencies greater than 10 kHz. Various optimization tasks are performed to reduce the receiver computational complexity. A fast implementation of the matching pursuit algorithm is tested on the DSP platform. Its performance, in terms of accuracy and run-time, is compared with that of the basic matching pursuit algorithm. Experimental results of the transmission and demodulation of binary phase-shift keying signals at three different symbol rates were obtained in the local Delaware Bay. The low bit error rates demonstrate the effectiveness of our implementation.