一种鲁棒性强的OFDM 水声通信系统*

为了在不同衰落水声信道下实现正交频分复用水声通信,该文提出了一种鲁棒性强的正交频分复用水声通信方案,方案包括编码调制、信道估计和多普勒估计等内容。为了使该系统更稳健,整个信道编码分为两个步骤。首先,循环冗余校验编码器和里德-所罗门编码器用于编码整个数据包,然后循环冗余校验编码器和Turbo 编码器用于编码每个数据帧,其中比特交织编码调制技术用来对抗信道的时变特性。为了得到水声信道估计,使用线性最小均方误差估计器来处理导频数据得到信道估计值。多普勒估计包括帧的多普勒估计和符号的多普勒估计。实验结果表明该系统在不同的衰落信道下都能实现正确的跟踪和译码,系统的鲁棒性能优越。此外,该系统算法计算简单,易于实现,具有良好的工程应用价值。     

采用时反和时频差分OFDM的水声语音通信方法

针对水声信道多径、时变、多普勒等恶劣传输特点对水声语音通信的严重影响,本文采用多通道时间反转和时频差分OFDM进行水声语音通信技术方案设计,该方法首先通过多通道时间反转进行时间域和空间域多径聚焦,进而结合时频差分OFDM调制解调抑制残留多径的影响。由于无需采用信道估计和均衡算法,系统实现方便、复杂度低,同时对信道具有一定程度的稳健性。该方法语音压缩编码采用混合激励线性预测编码。仿真实验和海试实验表明了本文方案的有效性。     

深海远程正交频分复用水声通信块间迭代稀疏信道估计方法

在深海远程正交频分复用(OFDM)水声通信中,信道时延长、频率选择性衰落严重,传统的块独立压缩感知稀疏估计需要较高导频插入密度才能保证一定的估计性能,通信频谱利用率较低。提出了一种基于信道稀疏时变建模的块间迭代信道估计方法,利用深海信道在两个相邻OFDM数据块之间的时间相关性建立块间信道稀疏多途结构的时变关系,在此基础上,对传统稀疏信道估计算法中的候选字典矩阵的字典原子进行删减并改进优化方程,实现了对前一数据块所估信道信息的有效利用,显著降低了信道估计所需的导频插入密度。在深海不同接收深度、不同距离条件下开展了海试验证,实验结果表明,与传统稀疏信道估计方法相比,本方法在导频插入密度减半的条件下可达到优于传统方法的估计性能。     

基于高速移动通信的虚拟天线阵列理论研究

在高速移动通信中, 多普勒频移对通信性能产生严重的影响, 通常需要对接收信号的多普勒频移进行估计并进行补偿. 本文研究在对单个天线接收的高速移动通信信号进行频移估计和补偿的基础上产生多路无频偏的信号, 并虚拟为天线阵列的输出以提高系统的接收增益. 首先讨论了“均匀时间采样”和“均匀相位采样”的关系, 并根据两者之间的关系提出了补偿多普勒频移和虚拟天线阵列的算法, 即对采样信号进行插值、均匀相位抽取以后, 再进行均匀时间采样. 然后分析了算法对高速移动通信系统性能的改善作用, 并提出了算法的硬件实现结构. 通过数值仿真验证了算法的干扰抑制能力和误码性能, 结果表明本文提出的虚拟天线阵列算法能够改善飞机、高铁上的高速移动通信系统的性能.     

垂直水声通信中的伪随机序列精确定时算法*

针对垂直水声通信中时变多普勒引起的定时偏差问题,研究一种基于伪随机序列的迭代定时估计及补偿算法。该方法利用伪随机序列作为同步信号,分三步估计时变多普勒：采用低复杂度的模糊函数法粗补偿接收信号内的平均多普勒;通过迭代插值法实现残留时变多普勒的精确估计及补偿;利用基于信道相关函数的相位信息,纠正均衡后信号的偏转相位。为实现高阶海试数据的有效解调,采用基于伪随机序列均方误差的多通道加权合并方式,获得空间分集增益。仿真及海试数据处理结果证明所提方法具有良好的时变多普勒估计及补偿性能,同时对30个通道内的1024QAM数据进行合并处理,在500 m的通信距离下,误码率为0.04,信道容量达到7.6 bits/symbol。与传统数据帧结构相比,无需使用线性调频信号,可以提高有效数据传输率。     

改进的多输人多输出正交频分复用水声通信判决反馈信道估计算法

针对最小均方误差准则下(Minimum Mean Square Error,MMSE)判决反馈信道估计算法在多输入多输出正交频分复用(Multiple-input Multiple-output Orthogonal Frequency Division Multiplexing,MIMO-OFDM)低信噪比水声通信环境下存在误码遗传缺陷,提出了一种基于压缩感知理论的改进的MMSE判决反馈信道估计算法。通过结合浅海水声信道的稀疏性特点,利用编码校验后的信息与原始信息实现了对信道估计的判决反馈更新,采用匹配追踪算法改进MMSE判决反馈追踪信道估计技术,实现了抑制传统判决反馈信道估计算法在迭代更新及传递过程中存在的误码遗传的目的。仿真和水池实验结果证实:改进的MMSE判决反馈追踪信道估计算法不仅可以有效的抑制误码遗传,对抗突发噪声,跟踪信道的缓慢时变,同时大幅降低了导频占用率,提高了通信质量。      

基于ZoomFFT的反多普勒频移算法在水声通信中的应用

提出了一种解决水声通信信号多普勒失配问题的方法——基于ZoomFFT的反多普勒频移算法。利用该方法能修正信号的多普勒失配,降低误码率。数值仿真和海上实验数据处理结果表明,该方法与常规滑动相关方法相比,计算速度快了2个数量级,计算所需的存储量减小了4个数量级,解决了水声信号移动通信过程中多普勒频移补偿问题。研究结果表明该方法可用于实际水下移动通信。     

变步长似p范数约束稀疏水声信道估计方法

针对范数约束类归一化最小均方(NLMS)算法在正交频分复用(OFDM)稀疏水声信道估计中误码率较高的问题,提出一种改进的变步长似p范数约束信道估计方法。采用改进双Logistic函数构造步长,并将误差信号自相关函数引入其中,实时调整步长和零吸引项,使得收敛速度和估计精度能够很好地折中。算法仿真结果表明,在浅海多径稀疏水声信道下,相比于传统方法,所提出的信道估计获得的最高性能提升为收敛速度提高72.3%,稳态误差降低95.9%。湖上试验数据处理结果显示,相比于传统信道估计方法,所提出的方法能使通信误码率降低2~3个数量级,实现零误码水声通信。      

深海远程正交频分复用水声通信簇约束的分布式 压缩感知信道估计*

在深海远程正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)水声通信中,信道时延较长,导致信道频率选择性衰落严重,传统的压缩感知信道估计算法性能大幅下降。为此,本文利用深海远程信道在一定时间内具有相关性并呈较稳定簇状分布的特点,在分布式压缩感知信道估计中引入簇区域信息,进行簇约束的多数据块联合稀疏信道估计,提出一种簇约束的分布式压缩感知信道估计方法,并在深海开展了定点远程水声通信实验进行验证,实验结果表明,与传统的分布式压缩感知信道估计算法相比,本方法的能够降低50%左右的误码率。     

基于高分辨谱估计方法的快速运动目标分析*

水下运动目标产生的声场由一系列不同模态的简正波组成,不同模态简正波具有不同的多普勒频率移动,携带了运动目标速度、频率等参数的信息。针对快速运动目标水下辐射声场的这一特点,采用高分辨谱估计Burg算法估计不同模态简正波多普勒频移,进而获得运动目标的速度、频率参数估计。数值仿真结果表明,高分辨谱估计Burg算法获得了高频率分辨率,在较短的观测时间或是阵元不足的情况下,较准确地估计了多普勒频移,获得了目标运动速度和初始频率等运动参数。     

正交频分复用无源时间反转信道均衡方法研究

针对水声信道多途信号引起的正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)水声通信系统符号间干扰的问题,提出了无源时间反转均衡的方法,将发送的探测信号时间反转与OFDM信号做卷积,利用无源时间反转镜的时间聚焦原理减小信道多途带来的符号间干扰,在OFDM符号中不使用导频的情况下实现信道均衡,简化了均衡步骤并提高了OFDM符号频带利用率。分析比较了无源时反均衡方法与最小平方信道均衡在水声多途信道下的误码性能。仿真研究和湖上实验表明,无源时反信道均衡算法可以有效的减小多途信道对OFDM水声通信系统带来的影响。      

时频编码水声通信技术研究

时频编码技术是利用信号码元不同时隙的不同频率进行二维信息编码的调制技术，具有较强的抗多途抗衰落能力，已被广泛应用于无线电短波信道和大气对流层散射信道，将其应用于多途效应严重的水声通信领域是一有价值的探索。     

Exploiting joint sparsity for underwater acoustic MIMO communications

MIMO communication has been recognized as a potential solution for high speed underwater acoustic communication, which unfortunately encounters significant difficulties posed by simultaneous presence of multipath and Co-channel interference (CoI). Sparsity contained in the multipath structure of underwater acoustic channels offers an effective way for improving channel estimation quality and thus enhancing the communication performance in the form of time reversal or channel estimation based equalization. However, for MIMO channels with extensive multipath and CoI, the performance gain achieved by classic sparsity exploitation channel estimation methods such as orthogonal matching pursuit (OMP) is still not enough to yield satisfactory performance. Under quasi-stationary assumption, underwater acoustic channels of adjacent data blocks exhibit correlated multipath structure, namely, multipath arrivals with similar time delay but different magnitude, which has not been exploited. In this paper, a joint sparse recovery approach is proposed to exploit the sparse correlation among adjacent data blocks to improve the performance of channel estimation. Under the framework of distributed compressed sensing (DCS), a joint sparse model which treats the multipath arrivals as sparse solutions with common time support is adopted to derive a joint sparse recovery algorithm for efficient channel estimation, the results of which are used to initialize and periodly update a channel estimation based time reversal receiver. Finally, underwater MIMO communication experimental results obtained in a shallow water channel are provided to demonstrate the effectiveness of the proposed method, compared to the same type of receiver that do not exploit the joint sparse.     

参量阵差分Pattern时延差编码冰下水声通信方法

为提高差分Pattern时延差编码水声通信方法的通信速率以及抗多途能力,使其能有效适用于冰下水声环境,提出了基于参量阵的差分Pattern时延差编码水声通信方法,推导了Pattern码的参量发射原理,分析了参量阵发射对该方法性能的影响,利用参量阵发射产生低频宽带窄指向性声柬,减少了声线触碰上下边界的次数,提高了系统抗多途的能力。冰下水域外场试验结果表明:本方法可有效抑制多途效应,同时低频宽带特性提高了系统通信速率。      

Multipath time delay estimation of underwater acoustic sinusoidal signals

To overcome the performance limitation of multipath time-delay estimation posed by underwater acoustic sinusoidal signals, an approach incorporating the frequency-domain weighting of the highly oscillatory Nonlinear Least Squares （NLS） cost function with the evolu- tionary optimization was proposed to facilitate the accurate estimation of the multipath timedelay of sinusoidal signals. In the described method, the number of the effective multipath signals, which is included into the parameter model as well as the multipath time-delay and amplitude factor, can be estimated simultaneously thus avoiding the requirement of additional computation. The experimental results performed with numerical simulation and sea-trial data are provided, demonstrating the effectiveness and precision enhancement of the proposed algorithm.     

字典奇异值分解加权压缩感知多径信号参数估计

为提高水声信道多径参数估计的分辨率,提出了一种基于字典奇异值分解的加权压缩感知算法。对于有源声呐,根据发射信号构造字典,对字典进行奇异值分解,利用大特征值对应的特征向量构造信号子空间,然后使用信号子空间对接收信号进行滤波。对滤波结果进行加权压缩感知参数估计,得出最终时延估计结果。仿真实验表明,所提方法能够对水声多径参数进行超分辨估计,适用于任何脉冲信号。湖试处理结果显示,混响背景下该方法也有较好的多径参数估计性能,能够降低接收数据的噪声成分,提高对水声信道的多径时延、个数和幅度的估计精度。      

The characteristic of sound propagation in deep water and underwater source localization in the direct zone

The multiple-path sound propagation in deep water is conducive to source localization of an underwater target.The transmission losses(TLs) and broadband pulse multiple-path propagation characteristics from a deep receiver is analyzed by using the experimental data from deep water area in the South China Sea(SCS).The results indicate that the width of the direct zone near the bottom of 4300 m water depth is about 30 km.The TLs in the direct zone near the bottom are much less than those in the shadow zone.It is meaningful for underwater sound source detection.Moreover,the time delay between the direct path and the bottomsurface-reflected path for a receiver near the bottom decreases monotonically with the source range.According to the linear relationship between the time delay of multipath and source range,a source localization method is presented to estimate the range of underwater target.The experimental results show that the estimated ranges are consistent with the global position system(GPS) measurements,and the mean square error of the estimation results is less than 0.28 km.     

参量阵差分Pattern时延差编码冰下水声通信方法（英文）

In order to meet the demands of underwater acoustic communication in under ice environment,a differential Pattern time delay shift coding underwater acoustic communication method based on parametric array is introduced in this paper.The under ice underwater acoustic channel is characterized by heavy multipath transmission.Under this model,a parametric array emission method of Pattern signal is derived and the system performance is analyzed.A broadband low frequency sound waves with narrow beam-pattern,which will reduce the interface reflections and suppress the effects of multipath transmission,can be obtained by the emission method.The Songhua River under ice trial results show that there is an anti-multipath property and a higher data rate in the under-ice acoustic channel in proposed approach.