数字签名算法及其比较

随着信息技术的发展,数字签名是电子商务、电子政务等应用的关键技术之一。文章介绍了数字签名的功能和基本原理,讨论了三类数字签名算法,并对比分析了它们在安全性能、计算速度、空间占用和通信带宽等方面的优劣。由于椭圆曲线数字签名各方面的优势,因而其具有很好的应用前景。     

半导体激光器驱动电路设计

设计了一种半导体激光器驱动电路,论述了半导体激光器的构造及其电路原理,阐述了半导体激光器驱动电路中恒流电路与恒压电路的工作原理与设计思路.通过在电路设计中增加恒压电路模块,有效地降低了半导体激光器的功耗.     

A simple remedy for the exaggerated extrinsic information produced by the SOVA algorithm

In this paper, we propose a novel and simple approach for dealing with the exaggerated extrinsic information produced by the soft-output Viterbi algorithm (SOVA). The proposed remedy is based on mathematical analysis and it involves using two attenuators, one applied to the immediate output of the SOVA and another applied to the extrinsic information before it is passed to the other decoder (assuming iterative decoding). The use of these attenuators aims at reducing the inherent strong correlation between the intrinsic information (input to the SOVA) and extrinsic information (output of the SOVA). We examine the modified SOVA (MSOVA) on additive white Gaussian noise (AWGN) and flat fading channels for parallel concatenated codes (PCCs) and serial concatenated codes (SCCs). We show that the MSOVA provides substantial performance improvements over both channels. For example, it provides improvements of about 0.8 to 1.0 dB at P/sub b/ = 10/sup -5/ in AWGN, and about 1.4 to 2.0 dB at P/sub b/ = 10/sup -5/ on fading channels. We also show that there are cases where the MSOVA is superior to the a posteriori probability (APP) algorithm. With this motivation, we extend the proposed modification to the APP algorithm with favorable results. We demonstrate that the modified APP (MAPP) provides performance improvements between 0.3 to 0.6 dB at P/sub b/ = 10/sup -5/ relative to the APP. We lastly mention that the proposed modifications, while they provide considerable performance improvements, keep the complexity of these decoders almost the same, which is remarkable.     

TC-BAC: A trust and centrality degree based access control model in wireless sensor networks

Access control is one of the major security concerns for wireless sensor networks. However, applying conventional access control models that rely on the central Certificate Authority and sophisticated cryptographic algorithms to wireless sensor networks poses new challenges as wireless sensor networks are highly distributed and resource-constrained. In this paper, a distributed and fine-grained access control model based on the trust and centrality degree is proposed (TC-BAC). Our design uses the combination of trust and risk to grant access control. To meet the security requirements of an access control system with the absence of Certificate Authority, a distributed trust mechanism is developed to allow access of a trusted node to a network. Then, centrality degree is used to assess the risk factor of a node and award the access, which can reduce the risk ratio of the access control scheme and provide a certain protection level. Finally, our design also takes multi-domain access control into account and solves this problem by utilizing a mapping mechanism and group access policies. We show with simulation that TC-BAC can achieve both the intended level of security and high efficiency suitable for wireless sensor networks.     

基于线性预测分析的语音信号合成

语音合成是实现人机语音通信的关键技术。文中介绍了一种基于语音信号线性预测分析的语音合成方法,以及什么是线性预测系数和如何提取线性预测系数,然后采用了重叠存储法,用预测系数合成语音。这种合成方法可以应用到语音信号的传输过程中,能减小信号的传输带宽,提高传输速率。     

显示器技术的未来之星——OLED

论述新型平板显示技术OLED的结构和类型 ,分析它的特点以及现状和发展前景 ,并指出应用于彩色显示器的有机发光显示器件OLED是未来平板显示技术的主流技术。     

Na~+掺杂量对BaBiO_3基陶瓷NTC特性的影响

以BaCO3、Bi2O3为原料,Na2C2O4为掺杂剂,用传统固相法制备了具有NTC特性的BaBi1–xNaxO3陶瓷。用XRD,SEM和ρ-t特性测量仪,研究了Na+掺杂量对该陶瓷的物相、显微结构及电性能的影响。结果表明:BaBi1–xNaxO3陶瓷的B25/85值和室温电阻率ρ25均随着x(Na2C2O4)的增加呈现先减小后变大的趋势;当x(Na2C2O4)为0.050时,获得了具有较好NTC特性的试样,其ρ25为2200?·cm,B25/85值为3365K。     

OFDM系统中DAGC的应用研究及FPGA实现

介绍IDFT/DFT精度在OFDM系统基带解调中的重要性,分析定点化DFT输入功率对其精度的影响,并在此基础上采用数字自动增益控制技术用于DFT前端,以解决过大输入信号动态范围所造成的DFT输出信噪比悬化的问题.理论分析、Matlab仿真结果以及FPGA实现结果表明,该方法具有可行性、实时性和易实现性,可使DFT输出信噪比达到最佳范围,以满足OFDM系统基带解调的要求;在较大输入功率情况下,采用DAGC技术的防溢出方法和经典DFT防溢出方法相比,前者使得DFT输出信噪比提高24 dB.     

异构网络中多无线电多信道环境下信道状态预测算法研究

该文针对异构网络环境未知性的特点,基于部分可测马尔科夫(POMDP)模型,结合认知无线电频谱侦测技术,提出了一种新的多无线电多信道环境下信道状态预测算法。该算法通过对信道状态历史信息的分析,推导出信道信念状态(belief state)的初始分布和转移概率,并以此选择出具有最佳回报的信道以供接入,从而达到提高信道利用率的目的。仿真结果表明算法性能要优于传统算法。     

瑞利衰落环境中一种能量有效的多无线电信道搜索机制研究

针对当前频谱搜索机制在能量有效方面的不足,该文提出了一种在瑞利衰落条件下基于部分可测马尔科夫决策过程(POMDP)的多无线电信道搜索机制MRCSS。该机制通过对瑞利衰落环境中信道状态建立POMDP模型来分析和推导出能效最佳信道,并以此指导用户的信道选择。仿真结果表明该机制能较传统搜索机制更有效地减少感知时间和节省能耗,从而达到提高频谱感知性能的目的。