国外保密系统介绍

文中介绍了多种国外保密系统,归纳了它们的特点。     

Cyclic Prefix Update for OFDM Amplify-and-Forward Relay Systems

We consider half-duplex amplify-and-forward (AF) relaying for increasing network coverage and spectrum efficiency of an OFDM-based cellular system. Due to the fact that OFDM symbols are transmitted over two serial multipath channels (i.e., the source-relay link and the relay-destination link) via AF relaying, the time spread of the received signal at destination nodes is introduced by both source-relay and relay-destination channels. Consequently, cyclic prefix (CP) added at the source node should have a much longer length than that of one-hop OFDM transmission to avoid inter-symbol interference. However, the increased CP length leads to the reduced spectrum efficiency of OFDM communications. In this paper, we propose a novel CP update scheme for achieving efficient and reliable multi-hop transmission in OFDM-based AF relay systems. By enabling the additional CP discarding and CP re-adding functionalities to relay nodes, the proposed scheme significantly reduces the required CP length without causing extra loss in the bit error rate performance, and therefore improves achievable end-to-end throughput and spectrum utilization efficiency. Simulation results confirm the theoretical analysis and illustrate the effectiveness of the proposed scheme.     

Age Replacement In Simple Systems With Increasing Loss Functions

Some age replacement policies are investigated and conditions for the unique existence of an optimum policy are derived. The optimum policy is the one which minimizes the expected cost per unit time over an infinite time span or maximizes the proportion of time during which the system is in operation. Losses have been expressed through increasing operating cost, if the objective is to minimize the expected total cost per unit time and through increasing renewal times if the objective is to maximize the availability of the system.     

Hybrid Bionic Systems for the Replacement of Hand Function

In recent years, thanks to the advancement of robotics and mechatronics, new and more effective devices for the restoration and replacement of sensory-motor function in disabled people have been developed. In all these systems, user acceptability is strictly connected to several issues such as the residual abilities of the subject, the mechatronic characteristics of the robot, and also the interface chosen to link them. It is possible to figure out different "human-interface-device" combinations [also defined as "hybrid bionic systems" (HBSs)] characterized by different properties in terms of level of hybridness, connection, and augmentation. In particular, in HBSs the interface has to be customized according to the characteristics of the robotic artefact to be controlled and to the desires and needs of the final users. In this paper, our attention has been focused on the problem of the replacement of hand function after amputation. Three HBSs characterized by different levels of complexity, dexterity, and sensorization are presented in order to show the possibility of developing acceptable and effective systems by choosing different levels of connection and hybridness (i.e., different interfaces) for different devices and applications. The following case studies are presented: 1) the use of invasive interfaces to the peripheral nervous system to control a dexterous and highly sensorized hand prosthesis; 2) the use of electromyographic signals recorded using surface electrodes to control a compliant adaptive prosthesis; and 3) the use of a foot interface to control a two-degrees-of-freedom prosthesis. The preliminary results achieved so far seem to confirm the idea that the correct choice of the proper interface while developing an HBS can increase effectiveness and usability     

基于循环前缀的OFDM系统定时同步估计算法

正交频分复用(OFDM)是一种多载波高效调制技术,由于能够有效地对抗无线环境中多径信道引起的码间干扰(ISI),近些年来受到越来越广泛的关注.同步是一切数字通信系统能够有效工作的基础.由于OFDM相对于单载波通信系统对同步误差更加敏感,因此同步技术更是OFDM系统中最关键技术之一.文中定量分析了符号定时同步误差对系统性能的影响,并详细给出了基于循环前缀的符号定时同步估计算法及其性能分析.通过仿真对各基于循环前缀同步估计算法进行了比较,给出了算法的应用场三合.     

On the Optimality of Cyclic Transmission in Teletext Systems

Teletext is a one-way information delivery system where pages of information are broadcast to all users in a continuous manner. System response time is an important consideration in the design of teletext systems. One factor contributing to response time is the order in which pages are transmitted. In this paper, we formulate the problem of determining the sequence of page transmissions as a Markovian decision process. Using this formulation we show that, from a response time point of view, a cyclic order of page transmissions is optimal. We also describe two algorithms for designing a teletext broadcast cycle.     

几个扬声器测试系统

简要介绍了基于PC机的扬声器测试系统在国内的使用状况。重点介绍了LMS，MLSSA，Clio，DAAS，SYSid5种测试系统的基本组成，测试条件和基本功能；比较了它们的异同；指出了在开发和生产中还存在的问题。     

A New Symbol Synchronization Scheme for Cyclic Prefix Based Systems

1　IntroductionFastFourierTransform (FFT)hasledtothesuccessofOrthogonalFrequencyDivisionMultiplex ing (OFDM)inxDSL ,IEEE80 2 .1 1a[1 ] andDAB/DVB[2 ] .AndthekeyofOFDMalsoliesinthein troducedcyclicprefixwhichmakesfrequencydo mainequalizationeasytoimplementandavoidsInterBlockInterference (IBI) .Theideahasalsobeenadaptedtosinglecarriercommunication ,almost“asitis” ,yieldingthesamecomputationaladvantagesandavoidingthehighcrestfactorofOFDM .ForbothOFDMandCyclicPrefix SingleCar…     

Blind Symbol Synchronization Based on Cyclic Prefix for OFDM Systems

In this paper, a blind symbol synchronization algorithm is presented for orthogonal frequency-division multiplexing (OFDM) systems, and a new timing function based on the redundancy of the cyclic prefix (CP) is introduced. It proves that the maximum of this function necessarily points to the correct timing offset, irrespective of channel conditions when the signal-to-noise ratio is high. Using the timing function, the timing offset is estimated through a searching algorithm. Channel power profile and channel length information are unnecessary. Simulation results show that the proposed algorithm is robust and outperforms the existing CP-based algorithms, particularly in frequency-selective fading channels.     

Interleaving-Based Cyclic Delay Diversity OFDM Systems over Spatially Correlated Channels

Cyclic delay diversity employing multiple transmit antenna provides increased frequency selectivity and thereby improves the frequency diversity in coded orthogonal frequency division multiplexing (OFDM). However, spatial correlation due to insufficient spacing between transmit antennas degrades the diversity performance. In this paper, the correlation of effective channel frequency response (CFR) of CDD OFDM is analysed and then propose constellation rotation and adjacent interleaving (CRAI) scheme over spatially correlated channel. In the proposed scheme, the subcarrier constellation is rotated by a known angle and then imaginary parts of rotated adjacent subcarriers are interleaved. The squared Euclidean distance of the codewords is derived to show the effect of constellation rotation. Adjacent interleaving is shown to exploit the frequency diversity by reducing the variation in average channel power (ACP) due to spatial correlation. Simulation results reveal that the proposed scheme performs well in spatial correlated channel and thereby improves the bit error rate (BER) performance.     

Guest Editorial Introduction to the Focused Section on Mechatronics in Multirobot Systems

This Focused Section includes ten papers that cover advances in mechatronics that are applicable to multirobot systems. The introduction also includes highlights of related articles published in previous issues of the IEEE/ASME Transactions on Mechatronics.     

Introduction to the Special Issue on Application-Specific Systems,Architectures and Processors

Journal of Signal Processing Systems -     

关键性安全系统安全完整性概述

介绍关键性安全系统的安全与风险基本概念、安全完整性的实现,以及功能安全要求标准IEC61508：2010的结构、功能安全的要求与实现、安全完整性评估。