Pattern时延差编码四信道水声通信技术研究

本文所研究的是基于Pattern时延差编码（PDS）体制下的水声通信技术.PDS水声编码体制利用Pattern码片出现在码元窗的时延差值进行时延编码,通过码元分割,有效的降低了水声信道的多途干扰;通过频率分割划分四个通信信道,增加通信速率至1000bit/s.在接收端利用带通滤波器来实现通信信道分割,每个信道再应用拷贝相关器实现码元分割并估计出时延差值,完成译码.仿真实验表明,该系统适合于大量不同水声信道高可靠性工作,为水声通信网络化打下坚实基础.     

点对点移动水声通信技术研究

点对点移动水声通信是实现由活动和静止节点共同构成的水声数据通信网的关键技术之一. 对移动水声通信声信道特性进行了分析,指出不同途径到达的声线对应的多普勒频偏不一致,进一步加大了多途扩展产生的码间干扰的复杂性,不利于水声通信. 提出单阵元被动式相位共轭镜信道均衡技术,可实时自动补偿多普勒频偏,并聚焦多途信号. 将单阵元被动式相位共轭应用于Pattern时延差编码移动水声通信系统,进行了移动水声通信试验,湖试结果验证了其消除码间干扰性能及本文水声通信系统的鲁棒性. 关键词： 移动水声通信 被动式相位共轭镜 时变信道 码间干扰     

多途信道中卷积码的统计特性

假设水声信道中存在界面的一次反射波,我们研究了卷积码的统计特性。结果表明,由于卷积码的解码是一解卷积运算,在某些情况下,解码时可以分辨多途信号,把它们对齐、叠加,改善了误差概率;在另外一些情况下,则达不到这种效果。卷积码抗多途干扰的作用,如同在信道中垂直布设的声呐阵,对多途信号进行过滤。相比之下,卷积码容易实现得多。卷积码是抗多途干扰的优良编码信号。     

UMFSK水声通信技术研究

在MFSK基础上,本文提出了UMFSK信道编码方法。采用窄带调频和跳频调制技术,故在一定程度上抑制了由多途效应引起的码内/码间干扰;提出了基于UMFSK的实时信道标校技术,可对信道进行稳键均衡,抗信道多途引起的码内干扰。进行了湖试,取得了试验数据并进行了数据分析。分析表明：UMFSK可抑制码元相消干涉引起的码内干扰,其效果随码元调频带宽的增大而变好;信道标校技术可对信道进行稳键均衡,并由于结构简单,可做到实时实现。基于UMFSK的误码率为10^-3（通信带宽2kHz,速率100-150bps)。     

水声多途信道的维纳误差限信道质量量化分析方法

提出了一种定量分析不同多途结构的时不变水声信道对单载波水声通信系统性能影响程度的方法。该方法利用水声信道下信号线性均衡的残留均方误差与通信系统误比特率性能相关性强的特点,计算信号线性均衡的残留均方误差极限,并将其表示为只与信道冲激响应有关的变量,称之为维纳误差限(WEB),将此作为多途信道质量量化指标来评估多途信道对通信性能的影响。为验证方法性能,对比分析了大量海试实测水声信道下,线性均衡、判决反馈均衡以及Turbo均衡等单载波通信中3种常用信道均衡方法的误比特率与多种水声信道质量量化指标的相关性,利用Spearman相关系数对相关性进行量化分析,实验结果表明,相比于时延扩展、相干带宽、频谱衰落深度和信号多径比等传统信道多途特性量化指标,维纳误差限与均衡后误比特率的Spearman相关系数更高,平均相关系数可达0.71。利用维纳误差限可有效量化和分类不同质量的多途信道,定量体现不同水声信道多途结构对于通信性能的影响程度。     

浅海环境中的时间反转多用户水声通信

在无线电通信中,多用户通信可以采用时分多址(TDMA)、频分多址(FDMA)或者码分多址(CDMA)技术来实现,在水声通信中,信道的多途传播特性带来的空间差异,提供了另外的多用户通信手段。时间反转(或相位共轭)技术,能够实现对空间中指定点的聚焦接收和多途压缩,它为空间位置不同的多个用户提供了相互独立的通信通道,能够很好地克服用户之间的同道干扰(CI)。本文在垂直阵接收的基础上,利用时间反转技术来实现不同用户在同一信道中的同时通信,结合带锁相环的自适应判决反馈均衡技术来消除残余的多途码间干扰,并进行了初步的海上试验,实现了两个不同深度上用户的同时通信。     

数字时间相关积累(Ⅲ)——抗多途性能分析

本文首先探讨浅海声信道中多途的统计特性,在此基础上分析了DTCCA和DTACA抗多途的性能。理论估算和实验证明,这类信号处理方式抗多途性能是优越的,可以利用多途能量。     

一种新的水声通信体制

本文提出了一种针对海洋水声信道多途干扰的新的水声通信体制.它将利用信号码元波形参数进行多维信道编码技术和利用信号码元时延值进行信息编码技术融于信号码元的设计中,从而使得本方案具有很强的抗多途时延扩展能力,并可望获得相当高的通信速率.初步的湖上试验结果表明:在1公里左右的水平通信距离上,可靠的通信速率约为200bit/s     

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。      

菲律宾海声传播信道时空相关性变化实验

声传播信道的时空相关性变化主要由信道多途结构的时空变化所决定。一般深海声传播信道由于受海底底质影响小，多途结构相对较为简单，比较容易实现深海信道的修正匹配．本文利用拖曳式低频宽带大功率发射换能器，发射线性调频脉冲信号，在接收端利用拷贝相关和脉间相关处理，得出信道的时空相关性变化。由于采用了宽带长脉冲信号，经过处理后减少了噪声于抗的影响．实验结果证实：信道的时空相关性主要由信道的多途结构及其时空变化决定．信道的相干部分约占全信道的４０％．本文的实验结果对深海信道的修正匹配研究有一定参考价值。     

Waveguide invariant focusing for broadband beamforming in an oceanic waveguide

The performance of broadband sonar array processing can degrade significantly in shallow-water environments when interference becomes angularly spread due to multipath propagation. Particularly for towed line arrays near endfire, elevation angle spreading of multipath interference often results in masking of weaker sources of interest. While adaptive beamforming in a series of narrow frequency bands can suppress coherent multipath interference, this approach requires long observation times to estimate the required narrowband covariance matrices. To form wideband covariance matrices which can be estimated with less observation time, plane-wave focusing methods have been used to avoid interference covariance matrix rank inflation. This paper extends wideband focusing to the case of coherent multipath interference. The approach presented here, called waveguide invariant focusing (WIF), exploits a robust relationship for the frequency dependence of horizontal wave number differences. Unlike matched-field methods, WIF does not model multipath wave fronts but rather makes the interference appear to occupy the same rank-one subspace across frequency. This permits formation of wideband covariance matrices without interference rank inflation. Simulation experiments in a realistic ocean environment indicate that adaptive beamforming using WIF covariance matrices can provide a significant array gain improvement over conventional adaptive methods with limited observation time.     

Analysis and simulation of MDMA—A spectrum efficient non-orthogonal multiple access scheme for 5G communication

In this paper, an analysis and simulation approach is used to verify the performance of a recently proposed non-orthogonal multiple access scheme called multipath division multiple access (MDMA). The spatial multipath channel (SMC), which is the distinct feature for each user, is introduced to model the matrix channel of each user, taking into account the multipath structure and massive antennas. The signal and interference powers are then derived. Thus, the corresponding bit error probability can be approximated in a closed form. Moreover, computer simulation results are shown to be consistent with the analysis results. Most importantly, it is revealed that the MDMA system can achieve the superior cellular spectrum efficiency of 25 bps/Hz/cell which fulfills the 5G cellular system requirement.     

Spatial diversity and combination technology using amplitude and phase weighting method for phase-coherent underwater acoustic communications

The UWA channel is characterized as a time-dispersive rapidly fading channel,which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate intersymbol interference caused by multipath propagation, spatial diversity equalization is the main technical means. The paper combines the passive phase conjugation and spatial processing to maximize the output array gain. It uses signal-to-noise-plus-interference to evaluate the quality of signals received at different channels. The amplitude of signal is weighted using Sigmoid function. Second order PLL can trace the phase variation caused by channel, so the signal can be accumulated in the same phase. The signals received at different channels need to be normalized. It adopts fractional-decision feedback diversity equalizer(FDFDE) and achieves diversity equalization by using different channel weighted coefficients. The simulation and lake trial data processing results show that, the optimized diversity receiving equalization algorithm can improve communication system's ability in tracking the change of underwater acoustic channel,offset the impact of multipath and noise and improve the performance of communication system.The performance of the communication receiving system is better than that of the equal gain combination. At the same time, the bit error rate(BER) reduces 1.8%.     

适于干涉多光谱图像压缩的自适应率控制算法

提出了一种基于优化截取内嵌码块编码（EBCOT）的感兴趣区域（ROD编码干涉多光谱图像压缩方法。小波变换后,对1级分解的高频系数感兴趣区域即包含光谱信息区域进行垂直方向的分解,再对感兴趣区域进行比特平面提升。T1编码器对不同比特平面的编码过程（Codingpass）赋予不同的重要性权值,由高到低依次编码,T2编码器根据所得的比特率自适应地反馈控制T1的编码深度,最后进行率失真优化截取。实验结果表明,该方法提高了恢复图像质量,有效地减少了优化截取内嵌码块编码算法的计算量和内存使用量（bpp-1时,测试图像的整体、感兴趣区域和背景区域平均峰值信噪比均提高0．1dB以上,计算量和内存使用量平均减少40％和60％以上）,编码方式适合干涉多光谱图像压缩系统硬件实现。     

相干水声通信幅相加权空间分集均衡算法

水声信道的典型特点为多普勒频移严重、可利用带宽窄以及强多径干扰。空间分集均衡技术是相干水声通信中克服信道多径干扰,消除码间干扰的一种有效手段。为了极大化地输出阵增益,结合无源相位共轭方法和多通道均衡算法,本文设计了组合信噪干比的全新信道评价方法。利用改进的Sigmoid函数对各通道接收信号的幅度进行加权处理;采用二阶锁相环跟踪各通道信号的相位变化,实现各通道信号同相累加。将各通道低通滤波后的信号能量归一化,采用了分数阶-判决反馈分集均衡器,加入各通道权重系数实现了水声通信系统的分集均衡接收。仿真结果和湖试数据处理结果均表明,优化的幅相加权分集均衡接收算法能抵消多径和噪声的干扰,性能优于等增益合并接收算法。湖试数据处理结果误码率降低了1.8%。      

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。      

Experimental studies of applications of time-reversal acoustics to noncoherent underwater communications

The most difficult problem in shallow underwater acoustic communications is considered to be the time-varying multipath propagation because it impacts negatively on data rates. At high data rates the intersymbol interference requires adaptive algorithms on the receiver side that lead to computationally intensive and complex signal processing. A novel technique called time-reversal acoustics (TRA) can environmentally adapt the acoustic propagation effects of a complex medium in order to focus energy at a particular target range and depth. Using TRA, the multipath structure is reduced because all the propagation paths add coherently at the intended target location. This property of time-reversal acoustics suggests a potential application in the field of noncoherent acoustic communications. This work presents results of a tank scale experiment using an algorithm for rapid transmission of binary data in a complex underwater environment with the TRA approach. A simple 15-symbol code provides an example of the simplicity and feasibility of the approach. Covert coding due to the inherent scrambling induced by the environment at points other than the intended receiver is also investigated. The experiments described suggest a high potential in data rate for the time-reversal approach in underwater acoustic communications while keeping the computational complexity low.     

基于LabVIEW的特殊复杂信号源研究与设计

围绕导航通信系统的抗干扰测试需求以及对现役无线电导航系统的性能评估任务,研究并设计了一种复杂环境下的信号源并给出了数学模型。该信号源设计要求能够产生包括理想、多径、干扰以及信道噪声在内的、具有天线效应的实际复杂信号。在多径延时的设置上,给出了一种精度更高,延时任意的信号生成方法。最后以PXIe-5672为硬件测试平台,由计算机软件LabVIEW产生波形数据,并通过控制仪器驱动实现信号的存储和发生,完成了整个信号源的设计。仿真结果表明了该设计方案可行有效。