An improved decision feedback equalization using a priori information

This paper addresses the exhaustive computational complexity of the maximum‐a‐posteriori equalizer and the inefficiency of the conventional decision feedback equalizer (DFE) algorithm in iterative equalization, especially when the higher‐level modulation is used with severely distorted Inter Symbol Interference channels. The new method proposed here improves the bit error rate (BER) performance by computing the extra metric r_n+1 using the feedback symbols from previous iteration and combining it with a priori information of the symbols. After each iteration, the hard‐detected symbols are saved in the memory as a priori data for next iteration. We verified the proposed algorithm for Binary Phase Shift Keying and 8‐phase shift keying modulation. The promising simulation results show that the BER performance given by the proposed low complexity DFE algorithm improved dramatically throughout the iterations when the conventional DFE has only insignificant improvement in the process of iterative equalization. Copyright © 2009 John Wiley & Sons, Ltd.     

Fractionally spaced spatial adaptive equalization of S‐UMTS mobile terminals

In this paper we present fractionally spaced adaptive equalization techniques and space diversity combined receiver and evaluate their performance for the downlink of S‐UMTS system. The conventional ‘training’ (or non‐blind) and the ‘unsupervised’ (or blind) adaptive equalization algorithms are both investigated. Simulation results show that the equalizers are robust to Doppler shift and non‐linearity effects due to TWT amplifiers aboard the satellite. It is also shown that even with a moderate array size of two antenna elements, a significant improvement in terminal performance is achieved. Copyright © 2002 John Wiley & Sons, Ltd.     

A study of decoupling with skeleton matrix in two‐degree‐of‐freedom generalized minimum variance control

There are many multi‐input multi‐output (MIMO) systems in chemical plants, and they have multiple time delays of different length in each input and output pair. This paper explains a two‐degree‐of‐freedom (2DOF) control system based on generalized minimum variance control (GMVC) for MIMO systems. It can improve the tracking performance with respect to the reference signals and the response properties for the disturbance. The states between the sampling period can be expressed by using the modified z transform to take account of multiple time delays. Additionally, a tracking controller is designed to decouple the plant. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(1): 28–36, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21046     

Optimal delay estimation and performance evaluation in blind equalization

This paper deals with the problem of recovering the input signal applied to a linear time-invariant system from the measurements of its output and the a priori knowledge of the input statistics (blind equalization). Under the assumption of an i.i.d. non-Gaussian input sequence a new iterative procedure based on phase-sensitive high-order cumulants for adjusting the coefficients of a transversal equalizer is introduced. The main feature of the proposed technique is the automatic selection of the equalization delay so as to improve the equalization performance. A method for the a posteriori evaluation of the obtained accuracy in PAM systems is also introduced. It consists of the computation of an upper bound on the probability of error depending on certain moments of the equalizer output and the statistics of the channel input and therefore can be used in a blind equalization context. Based on the result of such a computation, it can be decided whether it is necessary to consider a longer equalization filter in the iterative procedure. © 1997 John Wiley & Sons, Ltd.     

矢量调制在相干多通道信号发生中的应用研究

对基于相干体制的多通道电子系统如MIMO通信、相控阵雷达、多通道侦察接收机等进行性能评估与测试一直是一个复杂、昂贵的过程,因为难以产生符合测试要求的多路相干信号。提出了一种基于矢量调制技术的宽频带相干多通道信号发生方法,分析了矢量调制器的非理想特性对多通道相干信号发生的影响,给出了解决思路。该方法具有频率覆盖范围宽、相位控制范围大、精度高、调节分辨率精细等优点,为基于相干体制的多通道接收机测试提供了一种高效便捷的信号模拟方法。     

基于直接序列扩频的WSN通信信道均衡算法

对无线传感器网络（WSN）通信信道进行均衡设计,抑制无线传感器节点之间的码间干扰,改善通信质量。提出一种基于直接序列扩频的WSN通信信道均衡算法。进行了WSN的信道模型设计,为了降低信道输出的稳态误差,采用时间反转镜为匹配滤波方法,进行多径信道的码间干扰滤波,设计自相关匹配滤波器,通过直接序列扩频方法实现WSN通信的信道均衡。仿真结果表明,采用该算法进行WSN的通信信道均衡设计,发射信号沿各个路径到达接收机的信号分量得到准确分离,信号的多径分量得到无误码接收,通信信道均衡效果较好,通信误比特率低于传统方法,改善了WSN通信质量,展示了较好的应用价值。     

Simulated comparisons of blind equalization algorithms for cold start-up applications

The open literature is replete with claims about convergence benefits associated with second-order-statistics (SOS) blind channel estimation/equalization algorithms. At the same time, the literature is sparse in addressing robustness concerns of these algorithms. This paper is intended to motivate interest in the study of such robustness concerns by providing a simulation-based comparison between some popular SOS algorithms and CMA for various classes of channels of interest to both the practitioner and researcher. © 1998 John Wiley & Sons, Ltd.     

SC—FDE系统信道估计与频域均衡算法研究与仿真

信道估计与频域均衡是单载波频域均衡(SC-FDF)系统的两大关键技术.对通信中信道的好坏进行估计,得到信道特征(CSI)是SC-FDE系统进行信道均衡的前提;而信道均衡即通过对估计出的信道衰减特征进行补偿,来减小信号在传输过程中所受外界的影响,信道估计与频域均衡性能的好坏共同决定系统最后均衡的效果.对SC-FDE信道估计和频域均衡技术不同的算法进行分析研究;在此基础上,结合两个模块进行联合仿真,得到性能最优的信道估计和频域均衡组合算法.     

Adaptive inverse control of unmodeled stable SISO and MIMO linear systems

Adaptive‐signal‐processing techniques have been employed with great success in such applications as: system identification, channel equalization, statistical prediction and noise/echo cancellation. From a mathematical point of view, there is little difference between these applications and the types of operations required by control systems to control a dynamical system. This paper presents an approach to control systems called adaptive inverse control in which adaptive‐signal‐processing techniques are used throughout. Adaptive inverse control comprises three simultaneous processes. The plant is automatically modeled using adaptive system identification techniques. The dynamic response of the system is adaptively controlled using the resulting model and methods related to channel equalization. Adaptive disturbance canceling is performed using methods similar to noise canceling. The method applies directly to stable single‐input single‐output (SISO) and multi‐input multi‐output (MIMO) plants, and does not require an a priori model of the system. If the plant is unstable, it must first be stabilized using conventional feedback. This implies that at least a rudimentary model need be made if the plant is unstable. Once the plant is stabilized, adaptive inverse control may be applied to the stabilized system. Copyright © 2002 John Wiley & Sons, Ltd.     

一种MMSE类盲均衡算法的凸组合策略

通常有2类重要的MMSE类盲均衡算法：恒模盲均衡算法和判决引导算法。前者面临收敛速度慢,剩余误差大的缺点;而判决引导均衡算法的收敛速度快,稳态性能好,缺点是启动条件不满足时算法会发散。本论文提出了一种MMSE类盲均衡算法的凸组合策略。通过应用凸组合的基本原理,恒模盲均衡算法可以自适应平滑地切换到判决引导模式。首先,提出了算法的凸组合策略,使得恒模盲均衡算法和判决引导算法之间可以自动软切换。然后描述了一种锚定过程,可以消除稳态时恒模均衡器过高的剩余误差,因此总的算法可以看作是经过了恒模均衡器训练的判决引导均衡。仿真实验证实了新算法的优异性能。     

A new blind source separation method based on fractional lower‐order statistics

We proposed neural network structures related to multilayer feed‐forward networks for performing blind source separation (BSS) based on fractional lower‐order statistics. As alpha stable distribution process has no its second‐ or higher‐order statistics, we modified conventional BSS algorithms so that their capabilities are greatly improved under both Gaussian and lower‐order alpha stable distribution noise environments. We analysed the performances of the new algorithm, including the stability and convergence performance. The analysis is based on the assumption that the additive noise can be modelled as alpha stable process. The simulation experiments and analysis show that the proposed class of networks and algorithms is more robust than second‐order‐statistics‐based algorithm. Copyright © 2006 John Wiley & Sons, Ltd.     

Design of multi‐input multi‐output minimum‐phase state control system with decoupling and feedforward compensation

This paper discusses the design of decoupling control for a multi‐input multi‐output (MIMO) linear system. A new configuration of the prepositional tandem matrix is presented as a decoupling compensator, and minimum‐phase state control is applied to the resulting decoupled system. In general, non‐minimum‐phase characteristics often accompany decoupled systems. Feedforward compensation makes the non‐minimum‐phase effect of each decoupled scalar system change to the delay time. A numerical example is given for the MIMO linear system, which conventionally results in non‐minimum‐phase systems. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(2): 53–61, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21117     

一种正交频分复用低压电力线通信系统的信道估计与迭代均衡策略

正交频分复用(orthogonal frequency division multi- plexing,OFDM)技术在低压电力线高速通信研究和应用领域获得了广泛重视。传统的OFDM系统通过对每个符号添加大于信道响应长度的循环前缀(cyclic-prefix,CP)来消除符号间干扰,使传输效率降低。提出一种低压电力线信息符号无循环前缀的OFDM通信系统的信道估计与迭代均衡策略,该策略采用m序列作为训练序列,利用其特殊的自相关特性,在系统接收端获得信道的时域响应,进而对无循环前缀的OFDM信息符号进行迭代均衡,以消除符号间干扰。仿真实验表明,该策略可提高传输效率、增强系统的抗噪性能、获得比传统OFDM系统更低的信道估计均方误差和误码率,且具有较低的计算复杂度。     

An Equalization Time Reduction Method Using a Pseudo‐Random Number Sequence for a Cell Voltage Equalization Circuit with an LC Series Circuit

When the cells of energy storage devices such as electric double‐layer capacitors are connected in series, it results in voltage imbalance in each cell because of the nonuniform properties of the individual cells. In a previous research, the authors proposed a novel cell voltage equalization circuit using an LC series circuit, and they examined the effectiveness of this circuit. However, the characteristics of the cell voltage equalization operation depend on each cell voltage difference. Therefore, the proposed circuit has a disadvantage that the equalization time tends to be longer than other cell voltage equalization circuits with a boosting circuit. This paper proposes an equalization time reduction method that uses a pseudo‐random number sequence generated by the linear congruential generators. The proposed method can reduce the average equalization time without adding any other active or passive elements. The effectiveness of the proposed method is verified through the experimental results. According to the experimental results, the proposed equalization time reduction method reduces the equalization time to 86.5% of the conventional method.     

Semi‐blind fast equalization of QAM channels using concurrent gradient‐Newton CMA and soft decision‐directed scheme

This contribution considers semi‐blind adaptive equalization for communication systems that employ high‐throughput quadrature amplitude modulation signalling. A minimum number of training symbols, approximately equal to the dimension of the equalizer, are first utilized to provide a rough initial least‐squares estimate of the equalizer's weight vector. A novel gradient‐Newton concurrent constant modulus algorithm and soft decision‐directed scheme are then applied to adapt the equalizer. The proposed semi‐blind adaptive algorithm is capable of converging fast and accurately to the optimal minimum mean‐square error equalization solution. Simulation results obtained demonstrate that the convergence speed of this semi‐blind adaptive algorithm is close to that of the training‐based recursive least‐square algorithm. Copyright © 2009 John Wiley & Sons, Ltd.     

Fractionally spaced blind equalization with low‐complexity concurrent constant modulus algorithm and soft decision‐directed scheme

The paper proposes a low‐complexity concurrent constant modulus algorithm (CMA) and soft decision‐directed (SDD) scheme for fractionally spaced blind equalization of high‐order quadrature amplitude modulation channels. We compare our proposed blind equalizer with the recently introduced state‐of‐art concurrent CMA and decision‐directed (DD) scheme. The proposed CMA+SDD blind equalizer is shown to have simpler computational complexity per weight update, faster convergence speed, and slightly improved steady‐state equalization performance, compared with the existing CMA+DD blind equalizer. Copyright © 2004 John Wiley & Sons, Ltd.     

An algorithm for direct identification of passive transfer matrices with positive real fractions via convex programming

The paper presents a new algorithm for the identification of a positive real rational transfer matrix of a multi‐input–multi‐output system from frequency domain data samples. It is based on the combination of least‐squares pole identification by the Vector Fitting algorithm and residue identification based on frequency‐independent passivity constraints by convex programming. Such an approach enables the identification of a priori guaranteed passive lumped models, so avoids the passivity check and subsequent (perturbative) passivity enforcement as required by most of the other available algorithms. As a case study, the algorithm is successfully applied to the macro‐modeling of a twisted cable pair, and the results compared with a passive identification performed with an algorithm based on quadratic programming (QPpassive), highlighting the advantages of the proposed formulation. Copyright © 2010 John Wiley & Sons, Ltd.     

Order and parameter estimation of time‐varying system by subspace method

This paper proposes an identification algorithm for time‐varying systems. We apply subspace method for estimation, since it is known to be useful when the input–output (I/O) data are observed by multi‐input multi‐output (MIMO) systems. Among many proposed techniques of subspace methods, we use MOESP (MIMO Output‐Error State Space model identification) in this paper, which assures arithmetic stability by RQ factorization and singular value decomposition (SVD). Generally, subspace methods can be applied after I/O data collection, so that we introduce updated steps of matrices for PI‐MOESP, which uses past inputs for instrumental variables. We propose a recursive update algorithm of PI‐MOESP, including estimation step of the system order, and consider some parameters inherent to the algorithm, namely, initial number of data, estimation step of the order, and forgetting factor. A numerical example shows the usefulness of the proposed method. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(2): 57–64, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20169     

基于小波分量奇异值分解的单通道盲分离算法

针对单通道盲分离领域先验信息不足的问题,提出了一种基于小波变换、奇异值分解和独立分量分析的单通道盲分离算法.首先对单路传感器接收的信号进行小波分解和重构,得到一组代表原始信号特征的细节信号,对其施加奇异值分解并剔除小于门限值的奇异点,以此消除干扰信号和噪声的影响.然后将经过处理的细节信号组作为独立分量分析算法的输入信号...     

A comparison of cyclostationary blind equalization algorithms in the mobile radio environment

In this paper we address the problem of blind equalization in the mobile radio environment using cyclostationary techniques, where the channel is generally non-minimum phase and the phase information of the system has to be preserved. Conventional second-order statistics applied to the received signal sampled at the symbol rate do not preserve phase information and therefore cannot be applied to identify separate minimum-phase and maximum-phase zeros of the channel. It has been shown that phase information can be preserved using only second-order statistics if the received signal is sampled using fractionally spaced sampling. This paper deals with the issue of how the convergence of the cyclostationary blind equalization algorithms compares to conventional supervised methods in the pan-European mobile radio system GSM. The results suggest that the convergence speed of some of the actual cyclostationary algorithms is fast for stationary channels but slow compared to conventional supervised non-adaptive (LS) and adaptive (LMS) algorithms in time-varying mobile radio channels. © 1998 John Wiley & Sons, Ltd.