浅海水声信道中的一种带循环均衡的Turbo译码结构

针对浅海水声信道长时延、强多途干扰的特点,建立了一种新的带自适应循环判决反馈均衡的Turbo译码结构,并对其性能进行了仿真研究.该结构对典型的Turbo译码器进行了改进,使之不但能输出信息比特,同时又能输出校验比特,这些比特经硬判决、符号映射及信道交织后反馈回判决反馈均衡器,构成带自适应循环判决反馈均衡的Turbo译码结构.厦门港实测5途浅海水声信道仿真结果显示,该结构具有优良的抗多途性能,信噪比大于4dB时,误比特率小于10-5,比联合判决反馈均衡的Turbo译码结构提高了约2.5dB.     

一种用于水声相干通信的快速自适应自最佳均衡器

多通道判决反馈均衡器(MC-DFE)是水声相干通信克服信道多径效应、消除码间干扰(ISI)的主要手段。本文提出了一种用于水声相干通信系统的分集合并自最佳自适应多通道判决反馈均衡器。该算法将快速自优化LMS分集合并(FOLMSDC)算法、快速自优化LMS(FOLMS)算法和快速自优化LMS相位补偿(FOLMSPC)算法有机地结合在一起。该算法一方面可以进一步减少运算复杂度,另一方面,由于算法中的步长因子和相位跟踪因子可以自适应地更新,因此算法可以更好地跟踪水声信道的变化,进一步提高通信系统的接收性能。仿真结果表明,本文提出的算法的性能优于现有算法。     

强多径干扰下的水声通信均衡算法研究

水声信道的典型特点为强多径干扰、多普勒频移严重。锁相环-判决反馈均衡器(Phase-Lock Loop-Decision Feedback Equalization,PLL-DFE)是水声相干通信中克服信道多径干扰,消除码间干扰的主要技术手段。对抗多径干扰的判决反馈均衡自适应算法进行了改进,在快速自优化LMS算法的基础上进行了优化,提出了记忆快速自优化均衡(Memory Fast-Optimized LMS,MFOLMS)算法。该算法提高了均衡器的跟踪性能。在二阶锁相环和判决反馈均衡器的联合作用下,按照最小均方误差(Minimum Mean Square Error,MMSE)准则自动调节相应的参数,使均衡器达到最佳的性能。仿真和湖试数据处理结果均表明,该文提出的算法可以抵消多径的影响,提高通信系统的接收性能。     

格型判决反馈均衡器在水声通信中的应用研究

阐述了自适应格型判决反馈均衡器,研究了它在水声通信中的应用,仿真比较了最小均方判决反馈均衡器(LMSDFE)、递归最小二乘判决反馈均衡器(RLSDFE)和最小二乘格型判决反馈均衡器(LSLDFE),并给出最小二乘格型判决反馈均衡器(LSLDFE)在湖试中的结果。     

适用于QAM信号的方形判决超指数迭代盲均衡算法

针对超指数迭代判决反馈(Super-Exponential Iteration Decision Feedback Equalization,SEI-DFE)盲均衡算法在水声通信系统中表现出的收敛性差的问题,提出了一种基于正方形判决的修正超指数迭代判决反馈盲均衡算法。该算法在修正超指数算法的基础上,引入判决正方形机制分别对输出信号的同相分量和正交分量进行均衡,以进一步提高相位补偿能力;在判决反馈均衡器中引入二阶数字锁相环,实现对相位旋转的跟踪和补偿。消声水池实验采用16QAM调制信号,从滤波器阶数、步长以及Q矩阵大小三个方面对算法的影响来验证算法的误码率性能,结果表明,新算法的误码率相比修正超指数迭代判决反馈(Modified Super-Exponential Iteration Decision Feedback Equalization,MSEI-DFE)算法改善了两个量级,实现了对相位旋转的有效补偿,大大改善了载波恢复性能。     

拟牛顿优化BP网络盲判决反馈均衡器

针对水声通信严重多途效应导致的码间干扰,利用神经网络良好的非线性拟合能力,将盲判决反馈均衡器结构与神经网络相结合,同时通过拟牛顿算法提升神经网络的收敛速度,提出了一种拟牛顿优化神经网络的盲判决反馈均衡器.用两个单隐层误差反向传播(Back Propagation,BP)网络替换判决反馈均衡器前馈和反馈滤波器,利用拟牛顿...     

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。     

基于FPGA的判决反馈均衡器设计

介绍基于FPGA的判决反馈均衡器设计,均衡器中采样LMS算法;在使用相同算法的前提下,比较线性均衡器和判决反馈均衡器的性能及不同抽头系数的判决反馈均衡器的性能,用VHDL语言实现判决反馈均衡器,并在Active HDL仿真软件中进行仿真。     

基于协同优化算法的Reed-Solomon码迭代软判决译码

基于协同优化算法推导出一种Reed-Solomon(RS)码的迭代软判决译码(SDD)算法。该算法属于消息传递算法,具有严格的理论基础。仿真结果表明,该算法相对于硬判决译码(HDD)能够获得有效的软判决译码增益,对于(15,9)RS码在误帧率(FER)为4×10-4时有0.3~1.3dB的增益;同时译码复杂度低,具有很好的工程实用性。此外该算法是一类软输入软输出(SISO)译码算法,能够应用于以RS码为子码的复合码,如级连码和乘积码的迭代译码。     

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。     

基于硬判决的BICM-ID系统的迭代载波相位同步算法

在基于迭代译码的比特交织编码调制(BICM-ID)系统中,提出了一种利用译码产生的硬判决信息作引导的迭代载波相位同步的算法.该算法等效于期望最大化(EM)算法,收敛于最大似然(ML)估计,利用Viterbi译码过程中产生的数据比特硬判决信息,通过迭代地在同步和解码之间交换信息来完成联合解码和载波相位同步,实现了联合解码同步.仿真结果验证了该算法的有效性.在相偏θ∈[-20°,20°]时,其误码率性能最佳;在迭代次数达到5次时,误码率性能基本接近理想同步性能,较传统的相位同步算法具有更优的性能.随着信噪比的增大,能更快地逼近理想同步性能.     

差分协作系统中的软输入软输出多符号差分球形译码

在差分协作系统中,为了解决硬判决多符号差分检测(multi-symbol differential detection,MSDD)译码过程中,部分信息丢失导致性能损失以及该算法中最大似然检测计算复杂度高的问题,提出了一种软输入软输出的多符号差分球形译码(SISO-MSDSD)算法.该算法利用球形译码思想,在一定搜索范围内计算编码比特的对数似然比(LLR),去除先验信息可获得编码比特的外信息,经内部译码器判决得到源信息.仿真分析表明,比较硬判决MAP算法,SISO-MSDSD算法性能明显提高,且在信道频偏较大时,随着分组长度增加能有效提高检测性能.此外,在低SNR区域,SISO-MSDSD算法对复杂度的改善也十分明显.因此,SISO-MS-DSD可作为一种较好的软检测算法应用于差分协作系统中.     

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.     

Soft-decision array decoding for volume holographic memory systems

We study the use of soft-decision array decoding in a volume holographic memory (VHM) system that is corrupted by interpixel interference (IPI) and detector noise. Soft-decision methods can unify equalization and error decoding. A highly parallel array decoder is presented in the context of two-dimensional low-pass channel mitigation and error correction. The new decoding algorithm is motivated by iterative turbo-decoding methods and is capable of incorporating a priori knowledge of the corrupting IPI channel during decoding. The resulting joint detection decoding algorithm is shown to offer VHM capacity and density performance superior to that of hard-decision n = 255 Reed-Solomon codes in concatenation with a Wiener filter.     

Iterative reduced-state decoding for coded partial-response channels

The conventional iterative decoding based on the Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm rises exponentially in terms of channel memory length. In this paper, we propose a low-complexity soft-input/soft-output (SISO) channel detector based on tentative hard estimates fed back from the outer decoder in the previous iteration. The computational complexity of the proposed detector is polynomial in terms of the channel memory length. To demonstrate the performance/complexity tradeoff of the proposed detector, we present simulation results for 9-tap, 11-tap, and 12-tap channels. We show that the proposed detector significantly reduces the computational complexity with only slight performance degradation compared to the full-complexity BCJR algorithm.     

Algorithms for threshold level selection and decoder logic designin decision-aided symbol-by-symbol data receivers for magnetic recordingapplications

Symbol-by-symbol receivers comprise an important class of data receivers in digital magnetic recording applications. In systems where intersymbol interference (ISI) is high, these systems often use decision-aided decoding methods. A typical system employs threshold level detection followed by decoding logic. This paper presents an algorithm for selecting decoder threshold level settings and for generating the truth table for the decoding logic. By making use of all information available to the receiver, it is demonstrated that considerable reduction in the number of threshold levels required can be achieved in systems where the data encoding obeys run length limit constraints. It is also shown that selection of decode timing reference may have considerable influence on the number of threshold levels required. Application of the algorithm is demonstrated for several partial response signaling channels. A brief discussion is given on the similarities between the structure proposed by this paper and standard decision feedback equalizers     

A new LDPC decoding algorithm aided by segmented cyclic redundancy checks for magnetic recording channels

We introduce a new low-density parity-check (LDPC) decoding algorithm that exploits the cyclic redundancy check (CRC) information of data segments. By using the error detection property of the CRC, we can successively decode data segments of a codeword corrupted by random errors and erasures. The key idea is that the messages from the variable nodes with correct checksum are fixed to deterministic log likelihood ratio values during LDPC iterative decoding. This approach improves the decoding speed and codeword error rate without significant modification of the LDPC decoding structure. Moreover, the CRC is also used for an early stopping criterion of LDPC decoding. Simulation results verify our claims.     

Pilot overhead reduction in turbo coded OFDM systems employing an iterative channel estimation under low signal-to-noise ratio environments

The authors evaluate the improved energy and spectral efficiency by pilot overhead reduction of turbo coded orthogonal frequency division multiplexing (OFDM) systems employing an iterative phase estimation algorithm. Developed from the recently proposed iterative phase estimation schemes, the phase estimation and compensation process is embedded into the basic iterative turbo decoding process for the application to OFDM systems with just a slight complexity overhead. At each decoding iteration, sub-carrier phase rotations are estimated from the extrinsic information arranged in each sub-carrier and are compensated for the next decoding iteration. This enables the iterative phase estimation algorithm to successfully work under very low signal-to-noise ratios even without pilot symbols. The pilot symbols are just very rarely inserted only for breaking the erroneous phase estimation propagation frame to frame in case of large residual phase offset beyond reliable decoding range. Simulation results show that the iterative phase estimation algorithm drastically reduces the pilot insertion overhead and thus, it achieves improved spectral efficiency as well as bit error rate (BER) performance by saving pilot energy compared to the conventional method.