一种新颖的水声相干通信接收算法

为了克服水声信道的多径衰落,消除码间干扰,获得可靠的数据传输,提出了一种新颖的水声相干通信接收算法。该新型算法有两个优点:一是将自适应判决反馈均衡器和迭代译码技术相结合,二是译码采用Turbo译码原理,整个译码系统可以看作是串联迭代译码器,只是其中的内部译码器被编码比特对数似然率(LLR)计算器所取代,有效地降低了运算复杂度。同时,自适应判决反馈均衡器采用了变步长因子算法,改善了均衡器的收敛速度。仿真实验验证了该组合接收算法的性能     

水声通信多通道最大似然联合均衡译码方法

水平阵是水声通信中常见的阵列接收形式,但垂直阵也有重要的应用场合。文章提出了一种适用于垂直阵的水声通信多通道最大似然联合均衡译码方法,相比现有仅在信道均衡中叠加各通道信号的多通道判决反馈均衡方法(Multichannel Decision Feedback Equalizer, M-DFE),该方法利用最大似然准则,在一体化联合均衡译码过程中融合空间多通道接收信息,将空间增益直接用于抵抗水声信道多途衰落和译码纠错,有效提升了水声通信的性能。仿真结果表明,在误码率同样达到 10^-3的条件下,该方法所需信噪比相比 M-DFE方法可下降 2 dB。海上实验结果显示,在多种信道条件下,该方法实现正确译码的通信速率是 M-DFE方法的 1.25倍以上。     

一种浅海水声信道分数间隔自适应均衡算法研究

水声信道是最为复杂的数据通信环境之一,而具有重要军用和商用价值的浅海水声信道,其多径与频散效应更为严重。在浅海水声数字通信中,普遍存在着码间干扰和码内干扰效应,严重影响了水下通信的速度和质量。在判决反馈结构的基础上,采用分数的方法,提出了一种适用于浅海水声信道的自适应均衡算法,并通过计算机仿真实验与整数方法进行了性能对比。传输信号采用正交相移键控调制方式,以有效利用有限通信带宽。仿真结果表明,该算法获得了较快的收敛速度和较小的稳态误差,提高了水声通信的有效性及可靠性,因而具有良好的工程应用价值。     

一种码分多址水声多用户接收系统

研究了一种水声异步多用户通信非集中式接收机系统,将码分多址和空时自适应滤波、多通道判决反馈均衡相结合,克服多用户系统中的多址干扰（MAI）以及水声信道多途效应引起的码间干扰（ISI）,实现指定用户的正确接收。利用实测多通道浅海水声信道响应函数进行了三个用户的异步通信仿真,分别比较了空时滤波均衡与单通道直接解扩、空间分集合并均衡等接收算法的性能,显示了空时滤波均衡接收机在抑制多址干扰、码间干扰、正确区分不同用户等方面的优点。码分多址机制和空时滤波均衡结合使用的特点使系统适合于低速数据传输且水声信道变化较慢的场合。     

水声DS-CDMA通信中多相位假设码片速率自适应判决反馈均衡算法研究

研究了直接序列扩频码分复用(DS-CDMA)通信中基于多相位假设的码片速率自适应判决反馈均衡算法.水声信道的衰落和多普勒频移会严重影响扩频信号的相关特性,需要在做解扩频之前进行多普勒频移补偿和信道自适应均衡.将空间分集-多普勒频移补偿-自最佳自适应判决反馈均衡算法应用到DS-CDMA通信中,提出一种基于多相位假设的码片速率自适应判决反馈均衡算法,并用实际的千岛湖实验数据和仿真数据对算法性能进行了分析.结果表明算法以增加计算复杂性为代价显著提高了DS-CDMA通信性能,在复杂快变的多途和多普勒频移条件下可以保证低的误符号率,在低信噪比条件下能够稳定工作,总体性能良好.     

浅海水声信道中QC-LDPC码性能研究

针对大起伏、强多途、窄带宽的浅海水声信道需采用码长短、性能好、易于实时处理的信道纠错码技术才能提高水声通信系统可靠性的问题,提出了准循环低密度奇偶校验( QC-LDPC)码作为浅海水声信道的信道纠错编码方案.建立了QC-LDPC码在水声信道中的仿真模型,采用BP译码算法,在典型3径浅海水声信道中就码率、围长等参数对误码...     

基于VBLAST的水声MIMO高速通信技术研究

为实现高速水下通信,提出了一种基于VBLAST（贝尔实验室垂直分层空时）编码的水声MIMO（多输入多输出）通信技术。该技术通过在发射端和接收端同时采用多个阵元进行多发多收,借助空间复用,可有效解决水下通信系统带宽资源缺乏的难题,使系统在不增加带宽的条件下成倍提高数据传输速率。在水声MIMO通信系统的接收端,提出采用带有二阶数字锁相环、基于自适应空时判决反馈均衡的相干解调技术。该技术可有效克服水声MIMO信道中的多径干扰及同频干扰,且能自适应跟踪信道变化。仿真及湖试结果证明了所提水声MIMO高速通信技术的良好性能。     

单载波频域判决反馈均衡水声通信技术研究

水声信道中多途干扰严重,由多途效应引起的码间干扰是影响水声通信系统的关键性因素。单载波频域均衡(Single-Carrier Frequency Domain Equalization,SC-FDE)技术基于正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)技术提出,能有效对抗水声信道中的多途干扰,同时能避免OFDM技术峰值平均功率比高的不足。文中先介绍判决反馈均衡算法,并与其他均衡算法的抗多途性能进行比较。然后为提高系统均衡的可靠性和水声信道带宽利用率,对传统数据帧结构进行改进。将独特字(Unique Words,UW)序列均分,提高水声信道估计的精度,进而降低误码率,增加传输的可靠性;增加数据帧中有用信息符号,系统误码性能几乎不变,水声信道频带有效利用率提高。最后开展水池试验,验证了算法的有效性和可靠性。     

极化码在OFDM水声通信中的应用研究

极化码（Polar code）因其高可靠性、实用的线性编、译码复杂度和理论上唯一可达香农极限等特点,成为信道编码领域新的研究热点。其编、译码方法的研究扩展至多种信道类型和应用领域,但在水声信道中的理论证明和应用研究相对较少且滞后。针对具有显著多途、多普勒扩散和有限带宽等复杂特性的水声信道,文章提出了与之相匹配的极化码信道编码机制;并结合正交频分复用（Orthogonal Frequency Division Multiplexing,OFDM）技术搭建水声通信仿真系统,研究极化码在OFDM水声通信系统中的性能表现;同时研究极化码在不同的水声信道模型、信道参数、码长、码率下的性能。仿真结果表明,在信噪比为4 dB时,码率为1/2的极化码在水声时变信道中的误码率可达10^-4～10^-5,优于低密度校验（Low density Parity Check,LDPC）、Turbo码,约有0.5～1 dB的性能增益,该极化码信道编码机制与水声信道相匹配,可有效提高水声通信的可靠性。     

码率兼容QC-LDPC码在水声通信中的应用

针对水声信道复杂多变、强多途和大起伏干扰等特点,提出采用码率兼容QC-LDPC码的自适应信道编码技术,以提高水声数据传输的可靠性和水声信道的信道吞吐率。建立了码率兼容QC-LDPC码在水声信道中的仿真模型,构造码率为1/2、2/3…5/6等一系列QC-LDPC码,在三种典型的水声信道中对其性能进行仿真。结果表明所设计的码率兼容QC-LDPC码在三种不同信道下可行有效,能较大地提高水声通信系统的性能。由于信道时延越长、信噪比越低,满足通信指标的码率就越低;并给出码率兼容QC-LDPC码在浅海水声信道中不同信噪比下满足通信性能指标的编码码率的查找表。码率兼容QC-LDPC码提高了水声通信的信道利用率,具有灵活的编译码性能,在水声自适应通信中具有很好的应用前景。     

Dual FDTS/DF: a unified approach to dual-detection and modificationfor MTR codes

Dual-detector decision-feedback schemes have recently gained considerable interest in magnetic recording. Schemes such as dual decision feedback equalization (DDFE), M2DFE, and dual FDTS/DF are dual-detector versions of DFE, multilevel DFE (MDFE), and fixed delay tree search with decision feedback fixed-delay tree search with decision feedback (FDTS/DF) detectors, respectively. At high recording densities, the dual-detector versions significantly improve bit-error-rate (BER) performance and reduce error propagation. In this paper, we first give a unified approach to the bit-error-rate analysis of dual-detector decision feedback schemes in an attempt to highlight their relationship, and then we show that the performance of dual FDTS/DF reduces to that of DDFE for τ=0 and reduces to that of M2DFE for τ=1 with d=1 code constraint. Further, we extend the dual FDTS/DF detection scheme to maximum transition run-length (MTR) coded channels. On the basis of both BER and error event analysis, we propose a modified dual FDTS/DF detection scheme for MTR-coded channels that improves BER performance. The new scheme modifies certain bits in the detection profess for preventing the dominant error event. Simulation results on 6/7 MTR-coded Lorentzian channel show that the modified detector gives around 1 dB SNR improvement over the advanced (trellis-coded extended partial response) TC-E²PR detector     

Application of decision feedback equalisers based on multilayer neural network structures to compensate

Decision feedback equalisers (DFE) based on multilayer neural networks (MNNs) structure are simulated in a 10 Gbit/s optical channel of standard single mode fibre of 300 km. Simulation results show that the DFE based on the MNN structure significantly outperforms the traditional DFE in the equalisation of chromatic dispersion in medium to long haul optical communications (>220 km).     

Performance of a single-input multiple-output decision feedback equaliser for polarisation mode dispersion compensation

To compensate the performance degradation induced by polarisation mode dispersion (PMD) in high-speed optical transmission, a single-input multiple-output (SIMO) decision feedback equaliser (DFE) technique is proposed to combat all orders of PMD-induced distortion. The scheme is based on a new SIMO PMD channel model which utilises information embedded in both polarisation states. The performance analysis of the proposed PMD SIMO DFE scheme is provided along with explicit expressions for the filter coefficients. The analysis results show that the new scheme provides a significant improvement over using a first-order optical compensator and conventional DFE.     

判决反馈自适应均衡技术在水声数据传输系统中的应用

在海洋石油的开发生产中，可以用水声数据传输系统对水下生产装置和设备进行遥测遥控。影响浅海、中距离水声数据传输系统可靠性的主要因素之一，是水声信号传播中的多径效应干扰。文章针对计算机模拟实现的多径传播的水声接收信号，采用判决反馈自适应均衡(DEF)技术，消除多径效应引起的码间串扰，提高了水声数据传输系统的可靠性。文中给出了DFE的结构，采用FTF算法实现了DFE，并分析了算法实施后的抗干扰性能。计算机模拟实验表明，采用DFE后，传输系统的误码率降低了1．4倍。     

A Quasi-Exact Dynamic Finite Element for Free Vibration Analysis of Sandwich Beams

A Dynamic Finite Element (DFE) model for the vibration analysis of three-layered sandwich beams is presented. The governing differential equations of motion of the sandwich beam for the general case, when the properties of each layer are dissimilar, are exploited. Displacement fields are imposed such that the face layers follow the Rayleigh beam assumptions, while the core is governed by Timoshenko beam theory. The DFE model is then used to examine the free-vibration characteristics of an asymmetric soft-core sandwich beam with steel face layers and a rubber core. The natural frequency results for the first four modes, in this case, show the exact match between the DFE and ‘exact’ Dynamic Stiffness Matrix (DSM) formulations, using only a one-element mesh, justifying the use of Quasi-Exact (QE-DFE) title. Convergence-wise, the QE-DFE formulation also outperforms the conventional FEM, which makes it useful in benchmarking other studies or the examination of high frequency response where FEM requires the use of large number of elements in order to achieve better accuracy. The application of the DFE to a lead-core sandwich beam is also discussed.     

大气光通信中Turbo码的最大后验概率译码

为了精确实现对空间物体的测量,提出了利用线激光、单CCD相机、小孔成像与激光面约束模型的激光线测量法。引进三维信息已知的标准阶梯块作为激光面约束的标定块;由计算机控制摄像头对实物连续拍摄和实时处理,提取激光线上的像素坐标;利用建立的模型将二维坐标转换成三维坐标,再以点云的形式重构出物体,实现三维自动测量。实践中检测系统测量精度可达到0.05mm。     

Space-time decision feedback equalisation using a minimum bit error rate design for single-input multiple-output channels

A minimum bit error rate (MBER) decision feedback equaliser (DFE) designed for single-input multiple-output (SIMO) systems employing a quadrature phase shift keying (QPSK) modulation scheme is proposed. It is shown that this MBER design is superior over the standard minimum mean square error DFE in the SIMO scenario considered, in terms of the achievable system bit error rate. A sample-by-sample adaptive implementation of this MBER DFE is derived, which is referred to as the least bit error rate (LBER) algorithm. It is shown that for SIMO systems using a QPSK scheme, the LBER algorithm has a similar computational complexity as the simple least mean square (LMS) algorithm. Simulation results demonstrate that the proposed adaptive LBER-based DFE outperforms the adaptive LMS-based DFE, in both stationary and fading cases.     

Performance evaluation of decision feedback equalization for theLorentzian channel

Recently, equalization and detection techniques have been applied to the magnetic recording channel. For medium to high normalized recording densities (S⩾2), decision feedback equalization (DFE) represents the only performant equalization method. Despite many proposed schemes, no specific analytical performance has been evaluated yet when applying DFE to the recording channel. In this paper, we derive both the zero forcing (ZF) and the mean square error (MSE) performance measures for DFE to the Lorentzian channel. Simple expressions have been found and allow us to determine from which recording density the MMSE-DFE significantly outperforms the ZF-DFE. These expressions have also revealed to be useful to evaluate the loss induced when combining coding and DFE for the Lorentzian channel     

Cl对LiAlH4解氢性能影响的第一性原理研究

采用基于密度泛函理论的第一性原理方法,计算了LiAlH4-Cl体系的晶体与电子结构及稳定性能。计算生成焓发现,Cl-均可替代LiAlH4晶体结构中不同位置的H原子、[AlH4]单元体及占间隙位,其占位难易程度从易到难依次为:间隙位H2位H4位H3位H1位[AlH4]单元体。H原子解离能的计算发现:在Cl-替代[AlH4]单元和占据间隙位时,LiAlH4体系的结构稳定性变差,对应体系的放氢能力提高。其中,Cl-占据间隙位时,其对应体系放氢能力最强。费米能级附近能隙ΔEH-L值变小,对应体系的结构稳定性降低,是提高LiAlH4体系放氢能力的根本原因。