基于水声信道传播时延排序的分层空时信号检测

基于分层空时编码的多输入多输出技术是一种极具潜力的高速水声通信技术, 但要实现这种潜力需要复杂的空时信号处理方法, 以抵消来自水声信道的多径干扰和异步到达干扰, 以及叠加在接收端的各层信号之间的干扰. 对低复杂度的空时信号处理方案进行了研究, 提出了一种基于子信道传播时延排序的有序连续干扰抵消信号检测算法, 利用子信道间的传播时延差, 实现可使差错概率最小的最佳检测排序; 给出了利用信道估计, 以极低的计算量确定排序的方法, 从而可以大幅降低信号检测的计算复杂度. 采用低复杂度的单载波频域均衡来抵消水声信道中的码间干扰和异步到达干扰. 仿真结果表明, 基于时延排序的信号处理算法可以获得检测性能的改善, 而且性能增益在高数据率时更加显著. 研究结果表明, 采用有效的信号处理方法可使水声信道中造成信号检测干扰的传播时延成为改善系统性能的有利因素.     

基于改进卡尔曼滤波的水声通信盲自适应多用户检测算法

针对水声通信网络中遇到的多用户检测中目标用户的多址干扰等检测问题,提出了基于改进Kalman算法的盲自适应多用户检测算法,解决了多用户检测中的多址干扰对水声通信信道用户变动时的干扰抑制问题。仿真分析分别针对同步多用户、异步多用户通信过程,对比了传统Kalman算法及改进的Kalman算法的性能差异,通过仿真对比表明,改进后的Kalman检算法不需要训练序列即可以实现同步和异步通信状态下的多水声目标用户的盲自适应检测,改进后的算法目标检测的信干比比传统算法最大可提高6dB。新算法对于水下多用户检测、区分,准确、稳定的实现基于CDMA协议的快速水声通信具有重要意义。     

联合空时编码的水声多用户节点协同并行传输多址接人协议设计

针对水声信道长传播时延特点导致水声通信网吞吐量低的问题,提出了一种多节点协同并行传输的多址接入协议。该协议由接收端发起预约,在距离认知的基础上对预约节点划分协同传输小区,从而构建多用户节点的多输入多输出集中式网络架构;采用空时码对数据包编码,并合理规划数据包的发送时刻,使同一小区的多个用户节点发送的数据包在设定时间偏差范围内同时到达接收端,而不同小区的数据包以包链形式到达,实现多用户节点的无干扰、高效并行传输。仿真实验结果表明,与已有的其它两种协议相比,设计的协议通过空时复用的方法大幅缩短了平均端到端时延,显著提升了归一化网络吞吐量。      

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%。      

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     

双扩展水声信道的时延多普勒域稀疏估计

利用双扩展水声信道在时延-多普勒域存在的稀疏结构,将信道估计转化为压缩感知框架下的稀疏恢复问题可改善估计性能。但是,稀疏恢复经典方法如l_1范数、近似l₀范数无法适应水声信道时延-多普勒域稀疏度的动态变化,而匹配追踪(Matching pursuit,MP)、正交匹配追踪(Orthogonal Matching Pursuit,OMP)等贪婪类算法则存在着易进入局部最优解、二维搜索导致运算复杂度高等问题。提出在时延-多普勒域稀疏恢复的目标函数中引入非均匀范数约束(Non-uniform Norm Constraint,NNC),即在时延-多普勒域信道响应中根据每个时延-多普勒域位置的幅值分别分配为l₀或l₁范数约束,因而可通过不同范数约束组合的方式适应不同的时延-多普勒域稀疏度;同时,通过对非均匀范数代价函数进行梯度下降迭代求解并将梯度解投影至解空间推导了非均匀范数稀疏恢复的迭代求解方法,从而实现双扩展水声信道时延-多普勒估计。数值仿真和实验数据处理表明该算法相对经典方法有较明显的性能改善。通过仿真、海上水声通信实验结果可获取结论,利用时延-多普勒域稀疏特性的信道估计方法结合均衡器可有效提高双扩展信道条件下的水声通信性能。      

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     

正交时频空间调制移动水声通信方法

为提高移动水声通信可靠性,提出了一种基于正交时频空间(OTFS)调制的移动水声通信方法。针对水声信道长时延扩展的特点,设计了一种低复杂度交叉域Turbo迭代均衡算法,先在时域内对接收信号进行最小均方误差(MMSE)均衡,将均衡后的外部信息传递到时延-多普勒域进行软译码;再将译码后的软信息反馈回时域,作为下一次时域均衡的先验信息,实现均衡与译码的迭代检测。此外,针对OTFS水声通信中OTFS符号维度过大导致MMSE均衡复杂度过高的问题,采用了一种低复杂度MMSE算法,先利用矩阵对角线元素得到一组初始估计值,再将矩阵求逆问题转换为求解初始估计值与准确求解值之间的误差,继而通过对误差向量的不断迭代估计来实现低复杂度计算。湖试数据处理结果表明,所提方法可在最大移动速度4 kn的情况下实现OTFS信号的可靠检测。     

软件抗距离模糊技术在异步水声跟踪定位中的应用分析

异步水声定位系统可在目标信号发射时刻未知时对目标跟踪定位,此时发射和接收时钟存在固定时差。对于基于时延测量的长基线异步定位系统,当信号传播时延大于脉冲重复周期时,就会出现距离模糊。本文提出了在异步水声跟踪定位系统中软件抗模糊的思想,探讨了一种利用目标参考位置抗模糊的算法。从异步定位模型出发,得出等价的抗模糊准则,依据准则推导了算法及相应的参考位置取值范围,分析并克服了固定时差对算法的影响。海试结果验证了算法的可行性和有效性。     

OFDM水声通信系统中基于中继选择的资源分配算法

针对水声通信中继系统中系统容量和中继选择问题,本文提出了一种基于中继选择的资源分配算法。首先将每条中继链路的信道增益等效为虚拟直传链路的信道增益,然后在等功率分配的前提下,根据信道信息最佳原则,提出了一种中继选择及资源分配的多用户迭代算法,以实现对每个用户的传输链路进行选择和子载波分配,最后通过线性迭代注水算法进行功率分配。仿真结果表明,所提算法在保证目标速率的前提下,提升了系统容量。     

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.     

Multiuser interference cancellation in time-varying channels

In this letter, an adaptive time-reversal multichannel combiner is embedded within an iterative successive interference cancellation receiver. With the addition of matching pursuit, a sparse channel estimation technique, the combined receiver is shown to provide both temporal interference cancellation as well as spatial interference suppression in decoding simultaneous transmissions from separate users in a time-varying underwater acoustic environment. Experimental data collected during the KAM11 experiment illustrates that for a two-user multiple-access system, multiuser separation can be achieved.     

Asynchronous multiuser underwater acoustic communications (L)

An asynchronous multiuser system is proposed to support multiple-access underwater communications without the use of code-division multiple-access or a feedback channel. The rich multipath channels experienced by spatially separated users will be sufficient to ensure separation of collided packets at the base station. The iterative receiver will employ a combination of adaptive time-reversal processing, matching pursuit, and successive interference cancellation in a block-wise fashion to achieve multiuser separability. Data collected during the KAM11 experiment are used to illustrate the system's capability in a dynamic, time-varying environment.     

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。     

Delay and Doppler spreads in underwater acoustic particle velocity channels

Signal processing and communication in acoustic particle velocity channels using vector sensors are of interest in the underwater medium. Due to the presence of multiple propagation paths, a mobile receiver collects the signal with different delays and Doppler shifts. This introduces certain delay and Doppler spreads in particle velocity channels. In this paper, these channel spreads are characterized using the zero-crossing rates of channel responses in frequency and time domain. Useful expressions for delay and Doppler spreads are derived in terms of the key channel parameters mean angle of arrival and angle spread. These results are needed for design and performance prediction of systems that utilize underwater acoustic particle velocity and pressure channels.     

Statistical-mechanical analysis of multiuser channel capacity with imperfect channel state information

In this paper, the effect of imperfect channel state information at the receiver, which is caused by noise and other interference, on the multi-access channel capacity is analysed through a statistical-mechanical approach. Replica analyses focus on analytically studying how the minimum mean square error （MMSE） channel estimation error appears in a multiuser channel capacity formula. And the relevant mathematical expressions are derived. At the same time, numerical simulation results are demonstrated to validate the Replica analyses. The simulation results show how the system parameters, such as channel estimation error, system load and signal-to-noise ratio, affect the channel capacity.     

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.     

Iterative joint data detection and channel estimation for uplink MC-CDMA systems in the presence of frequency selective channels

This paper is concerned with joint multiuser detection and multichannel estimation (JDE) for uplink multicarrier code-division multiple-access (MC-CDMA) systems in the presence of frequency selective channels. The detection and estimation, implemented at the receiver, are based on a version of the expectation maximization (EM) algorithm and the space-alternating generalized expectation–maximization (SAGE) which are very suitable for multicarrier signal formats. The EM-JDE receiver updates the data bit sequences in parallel, while the SAGE-JDE receiver reestimates them successively. The channel parameters are updated in parallel in both schemes. Application of the EM-based algorithm to the problem of iterative data detection and channel estimation leads to a receiver structure that also incorporates a partial interference cancelation. Computer simulations show that the proposed algorithms have excellent BER end estimation performance.     

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.