保密通信中稳健差拍同步方法的描述与验证

结合自适应信道盲均衡和离散混沌系统的稳健差拍同步提出了一种存在信道畸变时的离散混沌系统的稳健差拍同步方法.该方法把混沌误差同步作为能量函数,利用进化算法训练递归神经网络完成自适应信道盲均衡,均衡器的输出作为混沌接收器的激励信号,从而在完成信道盲均衡的同时混沌系统达到同步状态.此外,提出了一种利用离散混沌系统稳健差拍同步实现存在信道畸变时的保密通信的方法.     

离散混沌系统稳健差拍同步方法及其在保密通信中的应用

本文结合自适应信道盲均衡和离散混沌系统差拍同步提出了一种存在信道畸变时的离散混沌系统的稳健关拍同步方法。该方法把混沌误差同步作为能量函数,利用进化算法训练递归神经网络完成自适应信道盲均衡,均衡器的输出作为混沌接收器的激励信号,从而在完成信道盲均衡的同时混沌系统达到同步状态。此外,本文提出了一种利用离散混沌系统稳健差拍同步实现存在信道畸变时的保密通信方法。     

应用粒子滤波器实现混沌通信系统的盲信道均衡

粒子滤波器(Particle filter,PF)是一种结合重要性权重抽样的序贯蒙特卡罗方法,能够应用到任意状态空间模型,并且能较好地估计经过非线性变化后的随机变量的统计特性.本文应用粒子滤波器和信号建模技术研究混沌通信系统的盲信道均衡问题,发展基于混沌的通信系统的盲均衡技术.仿真结果证实了,当Logistic映射作为混沌发生器和通信场景为固定参数与时变衰落信道时,该盲信道均衡器与基于扩展卡尔曼滤波算法的盲均衡器和基于无先导变换的自适应盲均衡器相比,有较好的均衡实现.此外,利用本文的盲均衡算法,实现了一种混沌调制通信系统的解调.     

小生境进化RBF网络在信道均衡中的应用

基于RBF网络的信道均衡器,其性能取决于神经网络的隐层参数.文中采用判决反馈均衡器的结构,RBF网络隐层的结构和参数则由基于小生境技术的混合递阶遗传算法来确定.仿真结果表明,这种RBF网络均衡器性能优良.     

Application of Recurrent Wavelet Neural Networks to the Digital Communications Channel Blind Equalization

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Blind equalization of quadrature partial response‐trellis coded modulated signals in Rician fading

In this paper, a blind maximum‐likelihood channel estimation algorithm is developed for quadrature partial response‐trellis coded modulated (QPR‐TCM) signals propagating through a Rician fading environment. A hidden Markov model (HMM) formulation of the problem is introduced and the Baum–Welch parameter estimation algorithm is modified to provide a computationally efficient solution to the resulting optimization problem. Performance analysis of the proposed method is carried out through the evaluation of bit‐error probability upper bound for Rician fading channels. Also, some illustrative simulations are presented. Copyright © 2001 John Wiley & Sons, Ltd.     

基于一种杂交学习算法的自适应复信道均衡技术

本文提出了一种基于多层前馈神经网络杂交学习算法的自适应复信道均衡的新方法。该学习算法用来训练一个输入、输出、权值和激活函数均为复数的神经网络。神经网络的训练利用了监督和非监督相结合的杂交技术,而权值的调整是基于TLS（total least square)准则进行的。计算机仿真结果表明,无论是在线性还是在非线性信道中,所提出的方法都表现出了很好的性能,这为自适应复信道均衡提供了一种新方法。     

放大转发协作分布式STBC-SC-FDE系统的频率域信道估计与均衡

针对单中继放大转发协作D-STBC-SC-FDE系统,研究了频率选择性衰落信道的频率域估计与均衡,给出了一种基于训练的最小二乘信道估计算法。该算法在Chu序列的辅助下,可在目的端同时估计直接信道S→D和级联信道S→R→D,算法可达最小均方误差。Monte Carlo仿真验证了算法的正确性,仿真结果也表明,信道的估计与均衡性能很大程度上受信道可用发送功率分配方案的影响。     

基于自适应噪声抵消的无线传感网络信道优化

无线传感器网络通信技术广泛应用在物联网近场通信、水声通信等领域。无线传感网络通信信道受到多途干扰,导致信道失衡,需要进行信道均衡模型设计。提出一种基于自适应噪声抵消的无线传感器网络通信信道优化技术,首先构建了无线传感器网络通信的信道模型,对无线传感器网络信道传播过程中衰减损失和各条路径的信号进行重组,采用自适应噪声抵消算法进行信道的多途干扰滤波,结合最小二乘（ RLS）准则算法进行无线传感器网络通信信道均衡设计。仿真结果表明,采用该通信信道均衡技术能有效提高无线传感器网络通信的信道质量,降低通信传输失真和误比特率,实现信道自适应均衡,提高通信的抗干扰能力。     

基于Turbo均衡和信道估计的单通道盲信号恢复算法

定时同步是单通道盲信号接收端处理的难点,提出了一种无需定时同步基于Turbo均衡的单通道盲信号恢复算法。该算法将定时同步偏差等效为符号间干扰（ISI,inter-symbol interference）信道,通过信道估计和Turbo均衡相互反馈软信息来改善源信号信息恢复性能。重点研究了初始盲均衡算法、信道估计算法、混合信号的MMSE均衡算法以及三者间的软信息交互。算法复杂度低、计算量小,适用于高阶调制信号。仿真结果表明,对BPSK、QPSK和8PSK信号,该算法都能得到较好的性能,且对等功率和不等功率信号同样适用。     

用滤波器组构成的传送多路复用器结构实现MMSE盲信道均衡

冗余滤波器组构成的传送多路复用器可以用来对FIR信道进行估计和均衡.本文提出一种在FIR滤波器组框架结构下,首先利用信号的相关矩阵对信道进行估计,然后在此基础上用MMSE准则下设计的FIR均衡器对数据进行均衡的盲算法.该均衡算法的性能要明显好于基于ZF准则的方法,并且在消除ISI的同时可以抑制噪声的影响,从而使系统的输出信噪比达到最优,而增加的复杂度很有限.文中最后在两种典型信道下对所提出的盲信道均衡算法进行了仿真,结果验证了上述性能.     

A compact dynamic channel assignment scheme based on Hopfield networks for cellular radio systems

In this paper, a new channel assignment strategy named compact dynamic channel assignment (CDCA) is proposed. The CDCA differs from other strategies by consistently keeping the system in the utmost optimal state, and thus the scheme allows to determine a call succeeding or failing by local information instead of that of the whole network. It employs Hopfield neural networks for optimization which avoids the complicated assessment of channel compactness and guarantees optimum solutions for every assignment. A scheme based on Hopfield neural network is considered before; however, unlike others, in this algorithm an energy function is derived in such a way that for a neuron, the more a channel is currently being allocated in other cells, the more excitation the neuron will acquire, so as to guarantee each cluster using channels as few as possible. Performance measures in terms of the blocking probability, convergence rate and convergence time are obtained to assess the viability of the proposed scheme. Results presented show that the approach significantly reduces stringent requirements of searching space and convergence time. The algorithm is simple and straightforward, hence the efficient algorithm makes the real‐time implementation of channel assignment based on neural network feasibility. Copyright © 2008 John Wiley & Sons, Ltd.     

Adaptive predistortion of COFDM signals for a mobile satellite channel

In this paper, we consider the optimization of the performance of QPSK and 16‐QAM coded orthogonal frequency division multiplexing (COFDM) signals over the non‐linear and mobile satellite channel. A high power amplifier and Rician flat fading channel produces non‐linear and linear distortions; an adaptive predistortion technique combined with turbo codes will reduce both types of distortion. The predistorter is based on a feedforward neural network, with the coefficients being derived using an extended Kalman filter (EKF). The conventional turbo code is used to mitigate Rician flat fading distortion and Gaussian noise. The performance over a non‐linear satellite channel indicates that QPSK COFDM followed by a predistorter provides a gain of about 1.7 dB at a BER of 3×10^?3 when compared to QPSK COFDM without the predistortion scheme and 16‐QAM COFDM provides a gain of 0.5 dB output back‐off and 1.2 dB signal to noise ratio at a BER of 3×10^?5 when compared with an adaptive predistorter based on the Harmmerstein model. We also investigate the influence of the guard time interval and Doppler frequency effect on the BER performance. When the guard interval increases from 0 to 0.125T samples and the normalized Doppler frequency is 0.001, there is a gain of 0.7 and 1 dB signal to noise ratio at a BER of 6×10^?4 for QPSK and 16‐QAM COFDM, respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

电力线OFDM/OQAM通信系统信道相位预处理均衡算法

针对电力线通信（PLC）正交频分复用（OFDM）系统存在频率掩码和频谱资源利用率低等问题,提出将正交频分复用/偏移正交幅度调制（OFDM/OQAM）技术应用到PLC系统中。该技术通过选用频率选择性较好的滤波器来抑制带外干扰,且不需要循环前缀,但是OFDM/OQAM系统在PLC频域复数信道下会产生严重的自干扰,传统的均衡算法并不能有效地消除OFDM/OQAM系统的固有干扰。针对这种情况提出了一种基于信道相位预处理的均衡算法。该算法的思想是让接收信号乘以一个信道相位调整因子,使等效信道的虚部尽量小,以此来减小接收信号中的干扰分量。仿真结果表明,与传统的均衡算法相比,所提算法在误比特率为1.0×10－6时可以获得0.5dB的性能提升。     

基于MIMO的可见光通信中的信道均衡

针对基于多输入多输出(MIMO)的室内可见光通信(Visible-Light Communication,VLC)系统中存在的码间串扰(ISI)问题进行了分析,并提出了适用于MIMO可见光通信系统的信道均衡方案及实现方法.仿真实验结果表明,该方法可以有效降低MIMO可见光通信系统中的码间串扰的影响.     

Improved auxiliary particle filter‐based synchronization of chaotic Colpitts circuit and its application to secure communication

In this paper, we propose a synchronization scheme based on an improved auxiliary particle filter (IAPF) for chaotic Colpitts circuit and conduct an experimental study on the synchronization performance with application to secure communications. Specifically, with the synchronization scheme, when the chaotic signals generated by an analog Colpitts circuit are transmitted through a nonideal channel, the distorted signals are processed digitally by the novelly designed IAPF at the receiver, in order to obtain the synchronized signals of the transmitter circuit. Experimental results indicate that synchronization can be achieved over both the additive white Gaussian noise channel and the multipath fading channel with low signal‐to‐noise ratio, even if there exist severe circuit parameter mismatches between the transmitter and the receiver. Furthermore, a chaos‐masking secure communication system is constructed and verified over both the additive white Gaussian noise channel and the multipath fading channel, and the bit error rate is evaluated versus different signal‐to‐noise ratios and symbol periods. It is shown that the achievable bit error rate can reach the order of magnitude of 10 ^{− 4} without error correction coding techniques. In addition, security analysis demonstrates that the proposed chaotic secure communication system is resistant to the brute‐force attack. Copyright © 2013 John Wiley & Sons, Ltd.     

Tree‐based channel assignment schemes for multi‐channel wireless sensor networks

Many sensor node platforms used for establishing wireless sensor networks (WSNs) can support multiple radio channels for wireless communication. Therefore, rather than using a single radio channel for whole network, multiple channels can be utilized in a sensor network simultaneously to decrease overall network interference, which may help increase the aggregate network throughput and decrease packet collisions and delays. This method, however, requires appropriate schemes to be used for assigning channels to nodes for multi‐channel communication in the network. Because data generated by sensor nodes are usually delivered to the sink node using routing trees, a tree‐based channel assignment scheme is a natural approach for assigning channels in a WSN. We present two fast tree‐based channel assignment schemes (called bottom up channel assignment and neighbor count‐based channel assignment) for multi‐channel WSNs. We also propose a new interference metric that is used by our algorithms in making decisions. We validated and evaluated our proposed schemes via extensive simulation experiments. Our simulation results show that our algorithms can decrease interference in a network, thereby increasing performance, and that our algorithms are good alternatives for static channel assignment in WSNs. Copyright © 2015 John Wiley & Sons, Ltd.     

基于序列自相关的信道估计与均衡算法FPGA实现*

针对传统的单载波频域均衡算法存在的受信道随机噪声影响较大的缺点,利用序列自相关性进行信道估计,有效解决了随机噪声对信道均衡的影响问题,并结合工程实际,在该信道估计算法的基础上,对频域均衡的实现进行了适应性改进。选用Altera公司的EP3C120F484芯片实现了该算法,设计了频域均衡系统的FPGA实现方案。经验证,该算法能同时适应多径和噪声干扰严重的复杂信道。     

Statistical analysis of co‐channel interference in wireless communications systems

Co‐channel interference is recognized as one of the major factors that limits the capacity and link quality of a wireless communications system. An appropriate understanding of the statistical behavior of the co‐channel interference is therefore required when analyzing and designing techniques that mitigate its undesired effects. The total co‐channel interference in a wireless communications system is usually modeled as the sum of lognormally distributed signals, and is generally assumed to be itself lognormally distributed. Based on this assumption, several methods for estimating the moments of the resulting lognormal distribution have been proposed. The accuracy of these methods has been studied in previous works, under the assumption of having all summand signals (individual interference signals) identically distributed. Such an assumption rarely holds in practical cases of emerging wireless communications systems, where co‐channel interference may stem from far‐away macrocells and nearby transmitters, causing the interference signals to have different moments. In this paper we present an analysis of the accuracy of two popular methods for computing the moments of a sum of lognormal random variables, namely Wilkinson's method and Schwartz and Yeh's method, for the general case when the summands have different mean values and standard deviations in decibel units. We show that Schwartz and Yeh's method provides better accuracy than Wilkinson's method and is virtually invariant with the difference of the mean values and standard deviations of the summands. Copyright © 2001 John Wiley & Sons, Ltd.     

Rake接收机在超宽带系统中的均衡性能分析

从缩短信道时延扩展的角度出发,研究了Rake接收机的部分信道均衡能力,并推导出了Rake接收机均衡性能与Rake接收机的复杂度和信道衰减系数之间的关系;分析了信道估计误差对Rake接收机合并前后多径信道变化的影响。研究表明当存在估计误差时,Rake接收机仍然能实现均衡的作用,但是性能有所下降;由于低复杂度Rake接收机引入的估计误差较少,在低信噪比条件下其均衡性能甚至会优于高复杂度的Rake接收机。