基于小波包的阈值语音去噪算法研究

传统的小波阈值去噪算法会不可避免地造成有用语音信号的损失,达不到很高的信噪比。基于Donoho提出的传统阈值去噪方法,提出了一种新的阈值函数,该闽值函数结合了软阈值函数和灿律阈值函数的优点,不仅克服了硬阈值函数不连续的缺点,而且解决了软阈值函数存在的恒定偏差。实验仿真表明,新阈值函数的语音去噪方法无论在听觉效果上,还是信噪比指标上均明显优于传统的硬、软阈值方法。     

一种基于DAA的强匿名性门限签名方案

针对目前大多数门限签名方案不能实现签名成员匿名或匿名效果比弱的问题,该文提出了一种带有子密钥分发中心的强匿名性(n, t)门限签名方案。方案主要基于可信计算组织在其v1.2标准中采用的直接匿名认证(Direct Anonymous Attestation, DAA)方案,以及零知识证明和Feldman门限秘密共享等技术实现。相较已有方案,该方案即使在签名验证者和子密钥分发中心串通的情况下,也能够实现子签名的不可追踪性,也即可确保子签名成员的强匿名性。分析显示,方案除具有强匿名性外还具备签名子密钥不可伪造、子签名可验证以及一定的鲁棒性等特征。该方案在匿名表决等一些对匿名性要求较高的场合中有着重大的应用价值。     

一种门限代理签名方案的分析与改进

通过对Qian-cao-xue的基于双线性映射的的门限代理签名方案分析,发现该方案并不满足强不可伪造性,任何人包括原始签名人可以伪造一个有效的代理签名,同时该方案也不能抵抗原始签名人改变攻击.在此基础上提出了改进的门限代理签名方案(方案1),改进的方案克服了原方案的安全缺陷.并把矢量空间秘密共享和多重代理签名结合起来,构建了一种更为广泛的基于访问结构的多重代理签名(方案2).门限代理签名方案(方案1)成为方案2的特殊情形.方案2中任何参与者的授权子集能产生多重代理签名,而非参与者不可能产生有效的多重代理签名,接收者可以通过验证方法验证个体代理签名和多重代理签名的合法性,而且能保证任何参与者都能检测出错误的子秘密.能抵御各种可能的攻击.     

基于模糊PCNN的小波域超声医学图像去噪方法

在分析了斑点噪声和PCNN的特点的基础上,将PCNN引入到小波域中,并结合小波软阈值去噪思想,提出了基于PCNN的超声医学图像软阈值去噪方法(ST-PCNN),该方法的优点是实现了在小波域中利用PCNN来识别高频信号的小波系数,并采用相应的方法处理小波系数,改善了PCNN难以确定斑点噪声的位置和采用固定阈值造成高频信号损失的缺点,更好的保留了低于固定阈值的高频信号的小波系数;在此基础上,将模糊算法引入到PCNN模型中,进一步提出了基于模糊PCNN的小波域超声医学图像去噪方法(F-PCNN-WD),该方法利用模糊算法来去除PCNN点火过程中大于点火阈值的斑点噪声的小波系数,以更好的去除斑点噪声。实验结果表明,ST-PCNN和F-PCNN-WD方法不仅能够有效地去除噪声,而且能够很好的保留图像的边缘和细节信息。     

完全子图的邻域重叠社团结构探测

为了能够更准确地对邻域重叠网络进行社团结构探测,研究人员对基于完全子图的社团探测算法进行了改进。在合并完全子图团簇时,计算每一对完全子图的重叠节点个数,设置合并完全子图的阈值,如果大于阈值,则合并。在处理不在团簇内的其他节点时,采用按照比例系数大小来划分规则进行划分。算法应用5-空手道俱乐部和科学家合作网当中,验证算法可以更准确地探测邻域重叠社团结构。     

干电池封口胶图像分割方法

高速高效生产是碳性电池的以后生产发展方向,而干电池封口胶质量直接影响干电池的寿命以及运输安全。利用机器视觉可以很好地检测封口胶质量,在生产线上获取的图像含有多个图像特征,无法使用单一阈值分割图像,在对比了多种阈值分割方法后,给出了一种较为理想的图像分割方案。     

典型通信电台带内干扰辐射效应研究

针对通信电台易受电磁干扰的问题,实验用正弦波作为干扰信号对正常工作的某型号通信电台进行带内电磁辐射的效应研究.根据GJB中对电台受干扰等级划分的相关规定,确定各种干扰程度的干扰等级.实验中通过改变各种影响因素,测试各种条件下电台干扰门限值.实验结果表明:电台受到带内干扰时,干扰信号频率与电台工作频差为15kHz以内,被试电台干扰门限值很小,且变化很小;当频差超过15kHz时,干扰门限值随着频差的增大急剧增大,干扰频率与电台工作频率越接近,电台受到的干扰随场强的变化越敏感.并且,电台的功率对电台带内干扰的门限值也有一定影响.     

An eigen‐select denoising threshold for channel estimation in OFDM systems

In reliable orthogonal frequency division multiplexing systems, channel estimator (CE) plays a crucial role. A pilot‐aided orthogonal frequency division multiplexing CE often employs denoising thresholds to identify significant and noisy channel impulse response taps. When the knowledge of channel statistics (KCS) is completely unavailable, the existing suboptimal thresholds require consistent estimation of one or more KCS parameters. In this paper, the effect of noise variance parameter estimation on CE's mean square error (MSE) performance is characterized analytically by computing threshold's tap‐detection probability. To mitigate MSE degradation due to KCS estimation, an eigen‐select threshold, which does not require any KCS estimation, is proposed. It utilizes eigen values of the auto‐covariance matrix formed by estimated channel impulse response. The proposed threshold is compared with existing state‐of‐art alternatives, for CE's MSE performance and system's BER performance, in correlated Rayleigh fading channel environments. Results reveal that, with the proposed threshold, performance plots converge to optimal solution more closely than the others. Copyright © 2015 John Wiley & Sons, Ltd.     

基于预测信息的空域水印改进算法

在图像的空间域中,一些像素与它相邻的像素之间存在一定的相关性,可以通过相邻的像素值来构建对这些像素的预测信息。基于此特点提出了一种利用参考像素点的预测信息来嵌入水印的方法,设计了重复嵌入水印的方案,通过阈值来控制嵌入水印的强度,分析了阈值对嵌入容量的影响。仿真结果表明,改进后的算法具有更高的水印容量,提高了抵抗剪切和噪声攻击的鲁棒性,且不依赖宿主图像的信息就可提取水印。     

一种门限代理签名方案的分析与改进

C-Y Yang等人提出了一个安全性基于求解离散对数困难性的门限代理签名方案,该方案具有较少的通信量及较高的计算效率。基于数论知识分析该方案存在缺陷：不满足不可伪造性和不可否认性,提出了改进方案将代理密钥以门限的方式在成员间共享,使得每个成员的子代理密钥都包含个体随机数,其他成员无法获知某成员的子代理密钥。改进方案的安全性基于求解离散对数的困难性,能抵御密钥替换攻击,具备不可伪造性和不可否认性。     

Optimization of multi-branch switched diversity systems

A performance optimization based on the optimal switching threshold(s) for a multi-branch switched diversity system is discussed in this paper. For the conventional multi-branch switched diversity system with a single switching threshold, the optimal switching threshold is a function of both the average channel SNR and the number of diversity branches, where computing the optimal switching threshold is not a simple task when the number of diversity branches is high. The newly proposed multi-branch switched diversity system is based on a sequence of switching thresholds, instead of a single switching threshold, where a different diversity branch uses a different switching threshold for signal comparison. Thanks to the fact that each switching threshold in the sequence can be optimized only based on the number of the remaining diversity branches, the proposed system makes it easy to find these switching thresholds. Furthermore, some selected numerical and simulation results show that the proposed switched diversity system with the sequence of optimal switching thresholds outperforms the conventional system with the single optimal switching threshold.     

Optimisation of depletion-mode transistors for an m.o.s. p-channel technology

Recent advances in p-channel m.o.s. integrated circuits are the result of using depletion-mode load transistors which provide currents proportional to the square of their threshold voltage. Using ion implantation, limits are set to the maximum obtainable threshold voltage depending on the implantation parameters. Their systematic investigation is reported and the resulting optimum parameters for threshold voltage shifts exceeding 6 V are given.     

GEO卫星轨道倾角变大后天线跟踪方法研究

针对某使用GEO卫星组网的卫星应用系统,由于GEO卫星寿命末期燃料不足,不能进行南北保持控制,轨道倾角不断变大,地面桁架式天线采用步进方式跟踪卫星困难的问题,研究提出天线的程序跟踪模式,并制定控制天线跟踪卫星的策略,即档位结合频度的控制策略。通过试验确定了最佳控制档位和频度,在实际应用中证明了该方法的有效性和优越性,解决了桁架式天线在卫星寿命末期准确跟踪GEO卫星的难题。     

基于微焦点X射线BGA焊点缺陷检测

BGA封装是是一种高集成的封装方式,其焊点缺陷会影响封装器件性能。为克服全局阈值分割、边缘检测方法对BGA焊点缺陷检测错误率较高的问题,本文提出采用Otsu阈值分割、轮廓提取、边界跟踪方法提取焊点轮廓,并用灰度形态学顶帽操作、直方图拉伸、Blob分析提取焊点气泡轮廓。通过分析BGA焊点缺陷类型及特征,提出基于焊点轮廓、气泡轮廓特征参数的焊点检测与分类算法。试验研究表明该算法较全局阈值、Canny算子焊点缺陷检测的准确率高,能够准确的完成焊点缺陷分类。     

基于小波变换和视觉特性的多光谱图像融合

本文提出了一种基于小波变换和人眼视觉系统特性的多光谱图像融合算法。首先对已配准的源图像进行小波多尺度分解;其次基于视觉系统提出一种新的融合规则,即分别将对应的高低频分量分割成若干个块,计算出每个块的对比度方差,通过文中所构造的一种自适应的阈值方法,选取两幅图像中清晰的图像块形成新的高低频分量;最后,通过小波反演变换重构多光谱图像。实验结果表明,这种方法不仅能很好的增强多光谱图像的空间细节能力及光谱信息,而且能避免增强结果出现振铃效应,是一种十分有效的融合方法。     

Square Geometrical Shaping 128QAM Based Time Domain Hybrid Modulation in Visible Light Communication System

We proposed two kinds of visible light communication(VLC)systems which respectively based on 64QAM/square geometrical shaping(SGS)128QAM time domain hybrid modulation scheme(SGSHY)and 64QAM/128QAM time domain hybrid modulation scheme(REGHY).These two systems can operate around specific forward error correction(FEC)threshold and maximize the achievable information rate(AIR)of the system.The principles of SGSHY and REGHY are proposed in detail,which has very low computation complexity compared with probabilistic shaping.The SGSHY outperforms REGHY at high peak to peak voltage(Vpp).Experimental results show that at high Vpp like 1.4V,which means the system is suffering from high nonlinear distortion,the AIR of SGSHY outperforms that of REGHY by 0.12Gb/s at the 2×10-2 FEC threshold.The AIR of the REGHY is at most 0.36Gb/s higher than that of 64QAM at 0.8V Vpp and 7%FEC threshold,while the(achievable information rate)AIR of SGSHY is at most 0.40Gb/s higher than that of 64QAM at 1.4V Vpp and 20%FEC threshold.     

基于视觉特性的Kirsch边缘检测算法

边缘是图像中最重要的信息之一,能够以较少数据量表达大量的图像信息。Kirsch算子有较好的检测效果及抗噪能力,但得到的边缘较粗,且阈值是一个不变值,自适应性差。针对以上问题,基于视觉特性理论提出了一种生成自适应阈值的方法,对已有的一种边缘细化算法提出了改进,获得了较好的效果。     

A new group-oriented publicly veriablethreshold signcryption scheme

Through cryptanalysis of the improved scheme of a generalized group-oriented threshold signcryption schemes, it is found that the improved scheme can effectively resist conspiracy attack and forgery attack, but does not have semantic security and public verification function, and sends threshold signcryption by the secret secure channel, which increases the communication costs and potential safety hazards of the system. A new group-oriented publicly verifiable threshold signcryption scheme is proposed on the basis of the improved scheme, the new scheme overcomes the drawbacks of the improved scheme, which not only provides with semantic security and public verification function, but also can send threshold signcryption by the public channel.     

Resplittable threshold multi-broker proxy re-encryption scheme from lattices

Two different encryption schemes and Lagrange polynomial were used to construct a resplittable threshold multi-broker proxy re-encryption scheme on the lattice,namely the encryption in the ciphertext input and output side was different from the encryption in the re-encryption side which make the bound of noise was more relaxed.Threshold multi proxy not only ensure the safety of re-encryption key,but also ensure re-encryption scheme can still work even if the individual proxy could not provide normal services.The scheme is proven IND-UniRTPRE-CPA secure.     

一种多径电力线信道下的主路径定时同步算法

分析了多径电力线信道特性,针对电力线通信信道中第一主路径非能量最强路径的定时同步问题,通过仿真分析信噪比与门限选择的关系,拟合了最优的第一主路径门限曲线,并提出了一种在多径电力线信道下寻找第一主路径的自适应定时同步门限选择方法,利用接发端前导信号互相关判决函数的峰均比关系自适应选择门限,用于解决电力线恶劣的信道环境下第一主路径非能量最强路径的情况下寻找第一主路径的问题。仿真表明,该方法同步性能明显优于固定阈值且接近于最优阈值的判决方法,相比固定门限有1 dB的提升。