读者·作者·编者

《信息与电子工程》编辑部:贵刊2008年4月第6卷第2期上刊登的《增强安全系统中独特码通信原则》一文,该文以安全性为前提,提出了独特码通信的三个原则并且进行了证明,但是论文求证不足,结论较为随意,现说明如下。     

低信噪比下独特码检测

该文分析了时分多址(TDMA)通信系统中独特码(UW)的检测和在低信噪比下独特码检测器的设计。提出了一种基于最大似然准则的通用的独特码检测器的工程实现方案。仿真结果表明它的性能比传统的硬判决-门限检测方法在码长为16和低信噪比条件下获得大约3-4dB的改善。该文所研究的独特码检测器已经应用于新近开发的通信系统中。     

无线实时图像保密通信密码同步技术研究

随着无线通信和信息安全技术的飞速发展,人们对无线实时图像传输的保密要求越来越迫切。无线通信由于受其信道和带宽的限制、密码同步码的插入,将会增加无线信道的信息载荷,降低无线信道的通信效率,造成密码通信失败或通信质量严重降低。针对实时图像传输保密通信系统强实时性和通信质量要求高的特点,研究无线通信系统中密码同步方法,采用独特的密码同步码的插入技术,提高图像传输保密通信的安全性和可用性。     

系统分布式LT码的构造

LT码是一类可现实的喷泉码,喷泉码由于其本身的特性可以克服深空通信中反馈难以实现,距离远,变时延的困难。依次介绍了在有中继传输的深空通信中适用的分布式LT码编码以及相对普通LT码编译码复杂度更低,系统开销更小的系统LT码。在此基础上提出系统的两信源分布式LT码的编码方法,并通过仿真结果验证其性能,为喷泉码在深空通信中的应用提供了一类性能优良的编码方案和建议。     

《无线电通信技术》第42卷总目次

信道编码是可靠通信系统中不可或缺的一个环节。从逼近Shannon容量限的角度介绍了信道编码技术的发展历史及现状,描述了几种重要的信道编码方法。重点论述了Turbo码、多元LDPC码、LDPC卷积码和Polar码等可逼近信道容量的现代编码方案,给出了这几种码的特点以及它们在深空通信、5G通信系统和光通信系统中的应用。     

低密度奇偶校验码在激光对潜通信系统中的应用研究

激光对潜通信系统光信道对光信号衰减极大,致使系统误码率增加,严重影响了通信系统的性能。因此必须采用具有极强纠错能力的差错控制编码技术来提高数据传输的可靠性,获得良好的通信效果。低密度奇偶校验码(LDPC码)是目前已知的距离Shannon限最近的纠错码。首先介绍了激光对潜通信系统的组成,然后分析了LDPC码的编译原理,最后仿真验证了在激光对潜通信系统中LDPC码的性能。结果表明LDPC码降低了系统误码率,改善了系统性能。     

窄带通信系统中信道编码系统的改进

由于卷积码具有编译复杂度低、易于实现的特点,在目前的实际通信系统中被广泛应用,但一些问题也随之而来.在需要长距离传输、通信质量要求很高的战术通信环境下,使用卷积码需要较高的发射功率,这导致了额外的能量损耗,限制了信息的传输距离,降低了通信系统的性能;而使用高性能信道编码可以在达到相同通信质量的同时降低所需的传输能量,进而改善系统整体性能.因此,通过研究Turbo码和LDPC码的基本原理,并结合实际通信系统的特点设定参数进行仿真,证明了Turbo码和LDPC码与卷积码相比,在相同的通信环境下具有更好的性能,能够有效地提高战术通信系统中信道编码系统的编码效率.     

大气激光通信系统中Turbo码译码性能仿真

由于大气激光通信信道对光信号的衰减极大,实际通信系统的编码应具有极强纠随机差错和纠突发差错的能力.针对大气激光通信信道的特殊性,结合当前优异的编码技术Turbo码对信道进行编码,通过对大气激光通信信道的分析对Turbo码编译码系统进行修正,建立了基于大气激光通信信道的系统模型,仿真分析了Turbo码实现低误码率的大气激光信息传输的可行性,并分析了采用不同算法和不同交织长度对系统性能的影响,为Turbo码在大气激光通信系统中的应用提供了理论基础.     

纠错码在自组网扩频系统中的应用研究

RS码作为一种性能良好的纠错码,广泛应用于无线通信系统中。结合自组网扩频定位通信系统功能目标,分析了无线定位通信系统工作流程对纠错的指标需求,选择了RS码作为纠错码,详细分析了不同长度的RS码对系统抗干扰性能的影响,并对RS码译码中的BM迭代译码算法进行了优化。     

自组网扩频系统中RS码的研究

RS码作为一种性能良好的纠错码,广泛应用于无线通信系统中。结合自组网扩频定位通信系统功能目标,本文分析了无线定位通信系统工作流程对纠错的指标需求,选择了RS的码作为纠错码,详细分析了不同长度的RS码对系统抗干扰性能影响并对RS码译码中的BM迭代译码算法进行了优化。     

Ad hoc mobility management with uniform quorum systems

A distributed mobility management scheme using a class of uniform quorum systems (UQS) is proposed for ad hoc networks. In the proposed scheme, location databases are stored in the network nodes themselves, which form a self-organizing virtual backbone within the flat network structure. The databases are dynamically organized into quorums, every two of which intersect at a constant number of databases. Upon location update or call arrival, a mobile's location information is written to or read from all the databases of a quorum, chosen in a nondeterministic manner. Compared with a conventional scheme [such as the use of home location register (HLR)] with fixed associations, this scheme is more suitable for ad hoc networks, where the connectivity of the nodes with the rest of the network can be intermittent and sporadic and the databases are relatively unstable. We introduce UQS, where the size of the quorum intersection is a design parameter that can be tuned to adapt to the traffic and mobility patterns of the network nodes. We propose the construction of UQS through the balanced incomplete block designs. The average cost, due to call loss and location updates using such systems, is analyzed in the presence of database disconnections. Based on the average cost, we investigate the tradeoff between the system reliability and the cost of location updates in the UQS scheme. The problem of optimizing the quorum size under different network traffic and mobility patterns is treated numerically. A dynamic and distributed HLR scheme, as a limiting case of the UQS, is also analyzed and shown to be suboptimal in general. It is also shown that partitioning of the network is sometimes necessary to reduce the cost of mobility management     

独特码及其编码原理研究

简要介绍了独特码基本概念，研究独特码应具备的性质并进行了相关证明，最后用实例验证了本文提出的独特码的分级编码方法。     

无线传感器网络中基于多比特量化的极大似然分布式估计方法

在无线传感器网络背景下的分布式估计中,由于传输网络对发送功率和传输带宽的限制,压缩信源冗余、降低通信数据量便成为一个重要的课题.为此,本文提出了一种基于多比特量化观测的分布式估计方法（MQS）,利用渐进性能作为优化准则构造量化阈值优化问题,运用粒子群算法对其进行求解得到最优量化阈值,给出了克拉美罗下界的解析表达式,并与均匀量化方法（UQS）和未量化方法（NQS）进行对比.理论分析和仿真实验表明,MQS的性能优于UQS.当量化深度增大到3时,MQS的估计性能十分接近NQS的估计性能.     

Traffic modeling for telecommunications networks

As new communications services evolve, professionals must create better models to predict system performance. The article provides an overview of computer simulation modelling for communication networks, as well as some important related modelling issues. It gives an overview of discrete event simulation and singles out two important modelling issues that are germane to extant and emerging networks: traffic modelling and rare event simulation. Monte Carlo computer simulation is used as a performance prediction tool and Markov models are considered     

军事通信抗干扰技术的发展现状及趋势

未来的战争是复杂电磁环境下的信息化联合作战,军事通信系统面临着日益复杂的干扰威胁。为了对抗各种通信干扰,夺取信息优势,世界军事强国纷纷研究和发展多种军事通信抗干扰技术。首先介绍了军事通信抗干扰技术的概念、原理、途径、特点和类别等基本知识,接着对正在发展的军事通信抗干扰技术进行了详细阐述,最后对军事通信抗干扰技术的发展趋势进行了预测和展望。     

Temporal Event Ordering with Fault Tolerance for Wireless Sensor and Actuator Networks

Temporal event ordering is an important issue in wireless sensor and actuator networks (WSAN) since actuators perform correct actions based on correct ordering among the time-related events. For temporal event ordering algorithms, they ensure that events captured from different sensors should be in the order. However, most of temporal ordering algorithms focus on the delay to transmit packets without considering the delay due to data loss. In the latter condition, the temporal ordering among events may be incorrect since some sensed data are lost due to the fail communication link or sensor. However, there is no literature for addressing the fault tolerance under the temporal event ordering of WSAN. Therefore, we propose a temporal event ordering with fault tolerance (TVOFT) in this paper. Differed from other temporal event ordering algorithms, TVOFT uses the routing table of each node with a acknowledge message once time to ensure the correct ordering of the time-related events. Therefore, the overhead of control packets also could be reduced in TVOFT. The simulations results demonstrate that TVOFT has the better correct event ordering rate and the less overhead of control packets than other temporal ordering algorithms even if the communication link or the sensor is fail.     

Cognitive radio sensor networks

Dynamic spectrum access stands as a promising and spectrum-efficient communication approach for resource-constrained multihop wireless sensor networks due to their event-driven communication nature, which generally yields bursty traffic depending on the event characteristics. In addition, opportunistic spectrum access may also help realize the deployment of multiple overlaid sensor networks, and eliminate collision and excessive contention delay incurred by dense node deployment. Incorporating cognitive radio capability in sensor networks yields a new sensor networking paradigm (i.e., cognitive radio sensor networks). In this article the main design principles, potential advantages, application areas, and network architectures of CRSNs are introduced. The existing communication protocols and algorithms devised for cognitive radio networks and WSNs are discussed along with the open research avenues for the realization of CRSNs.     

一种基于离散小波变换和RC6的信息隐藏算法

离散小波变换在离散随机数字信号处理中占有重要地位,论文提出了一种基于离散小波变换和RC6的信息隐藏方法,通过一系列运算将明文图像隐藏于掩饰图像中。此方法独特之处是文中设计了一个相当于密码本的位置矩阵表,它很好地解决了通讯双方的密码同步问题。由于使用只有通讯双方才知道的位置矩阵表以及每次通讯时位置矩阵表要进行混洗和掩饰图像加以更换,因此实现了密码设计中加密算法可以公开,密钥必须保密的设计思想,同时实现了一次一密。     

Cultural adaptation and information design: two contrasting views

Approaches to using visual language in a cultural context can be placed on a continuum, with global (universal) on one end and culture-focused on the other. Each approach reveals contrasting assumptions about three central design issues: perception, aesthetics and pragmatics. The global approach is characterized by attempts to invent an objective, universal visual language or to define such a language through perceptual principles and empirical research. The culture-focused perspective is founded on the principle that visual communication is intimately bound to experience and hence can function only within a given cultural context, to which designers must be sensitive. While the modernist, universal approach has been losing ground to the postmodern, culture-focused approach, the two complement each other in a variety of ways and, depending on the rhetorical situation, offer pragmatic benefits and drawbacks     

基于事件触发的微网分布式经济调度策略

针对传统微网系统分布式控制中通讯负荷重和有功功率经济分配问题,文中提出了一种基于事件触发的有功功率控制策略。各分布式电源在传统一致性算法的基础上采用事件触发方式,有效地减轻了通讯负担。各分布式电源通过事件触发控制器与邻居通信并相互交换有功功率信息,经事件触发控制算法得到最优有功功率值,实现成本最小化下功率经济分配。最后通过MATLAB/Simulink平台搭建微网系统模型,仿真验证了控制策略的有效性。