基于SLM的减小OFDM系统PAPR的改进技术

OFDM系统的峰均功率比过大是一个严重的问题.降低OFDM系统的峰均功率比中的选择性映射法(SLM)方法需传送边带信息,但边带信息传送需要严格的信道编码,增加了系统复杂性,占用了频带宽度.文中将传统的OFDM峰均功率比降低技术SLM方法加以改进并与限幅技术结合起来,所生成的新算法有效地弥补了传统SLM技术限制峰均功率比不足的问题,并且不用传输边带信息.仿真表明,该方法有良好的性能.     

视频点播在交互式多媒体教学中的实现

介绍了一种基于校园网的视频点播系统,分析了该系统的结构、功能以及主要特点,并阐述了建立该系统时的主要问题及采用的技术解决方法.     

基于Windows 2000的网站安全研究

简单介绍了防火墙、入侵检测安全技术,同时也简单介绍了网站负载均衡技术.分析了小型网站系统当前面临的主要安全问题以及相应的解决方法.并针对中小型企业网或者网站系统安全问题提出了一个解决方案.该方案基于Windows2000系统,结合防火墙、入侵检测以及负载均衡技术,为需要解决安全问题的网络系统提供了参考.     

基于DPCA的机载SAR-MTI系统误差分析及补偿方法研究

基于DPCA技术的机载SARMTI系统普遍存在的一个问题是:雷达平台的运动误差会导致DPCA条件不满足,从而引起系统杂波抑制性能下降.本文基于插值理论提出了一种针对该运动误差的补偿方法.本文从回波模型入手对系统误差进行分析,从理论上给出了运动补偿方法及其实现方法.该补偿方法的精度主要取决于雷达平台速度的估计精度,这个问题可以通过经典的运动参数估计方法得到很好的解决.计算机仿真结果表明,该方法能够有效补偿雷达平台的运动误差,提高SARMTI系统性能的稳定性,由于降低了对硬件系统的要求,这种方法在工程上易于实现.     

基于CDMA技术的新型防碰撞算法

标签碰撞是射频识别（RFID）技术的常见问题,该问题影响了RFID系统通信过程中数据传输的完整性.在分析已有防碰撞方法的基础上,根据帧时隙分组ALOHA算法,结合码分多址技术,提出了新型的标签防碰撞算法.该算法能够有效减小标签之间的碰撞概率,缩短读写器操作时间,提高吞吐率,很适合应用于具有较大数量标签的RFID系统中.     

基于状态观测器的一类混沌系统的投影同步

研究了基于状态观测器的一类混沌系统的投影同步问题.基于状态观测器方法和极点配置技术,设计出一种投影同步方案,使得一类混沌系统达到了投影同步.与以往的投影同步方法相比,该方法简便,易于实现,达到投影同步的时间短,并且在同步控制过程中可任意调整缩放比例因子.最后,用Lǖ系统进行了数值仿真,仿真结果进一步证明了该方法的有效性.     

扩频通信系统中一种消除干扰的编码捕获方法

针对恶劣环境下干扰信号影响捕获系统性能的问题,提出了一种消除强干扰的捕获方法,该方法利用奇异值分解技术,对接收信号进行分解、重构,以消除干扰,然后将处理后的信号送入捕获系统中进行编码捕获.理论分析与仿真实验均表明:该方法能够很好地消除干扰信号,有效地改善系统的捕获性能,提高系统的稳定性.     

基于散布矩阵分析的相关反馈算法及应用

相关反馈技术是一种较常用的提高信息检索精度的方法.在图像检索领域,相关反馈技术被认为是解决图像高层语义内容和低层视觉特征之间差异的一种有效方法.视觉特征的权值调整是一类应用较多的相关反馈技术,权值调整方法中存在矩阵奇异问题,本文提出了一种新的基于散布矩阵分析的相关反馈算法,解决了矩阵奇异问题.该方法通过分析与检索目标相关图像在特征空间中的散布来构造目标图像类的投影空间,该空间对应于一个高层语义类在特征空间中分布密集的子空间,在投影空间中计算相似图像;同时根据每次反馈的信息不断修正投影空间来提高系统的检索性能.在Cord图像数据库中的实验结果表明该算法具有良好的检索性能.     

全空域球面相控阵测控系统角跟踪方法概论

全空域球面相控阵测控系统是一类新的测控系统.在介绍该系统角跟踪技术特点的基础上,概述了角跟踪系统设计方法以及单脉冲角跟踪、圆锥扫描跟踪、变口径跟踪、多目标跟踪和过顶跟踪等技术,可供该领域相关人员参考.     

基于fal函数滤波的改进自抗扰技术的实现

自抗扰技术不但能观测系统的所有状态,还能观测系统模型不确定性及内外干扰,但该技术却忽略了测量噪声对系统观测的影响.基于解决测量噪声对观测系统精度的影响,提出了fal函数滤波方法,不仅能克服滤波后信号的幅值、相位与系统的真实输出差别较大的问题,而且具有快速收敛性和较高的滤波精度.仿真结果验证了该方法能够有效地滤除量测噪声...     

基于CDT的几乎同态问题探讨

范畴数据类型是基于范畴理论基础建立的，用于并行计算或框架结构设计中的并行操作。在链表上并行操作存在非同态问题。但有些功能可以转变为几乎同态来解决。文章对链表的几乎同态问题进行了深入的探讨，并得到了几乎同态定理，并通过事例在应用上加以论述。     

Posets and protocols-picking the right three-party protocol

In this paper, we introduce a framework in which we can investigate the possibility of adapting a security protocol in order to obtain optimal efficiency according to the communication channels available. This method is based on the observation that there is a partial order imposed upon the actions of the various parties involved in a protocol. We define operations permitted on the partially ordered set associated with the protocol and obtain transformations of the original protocol while preserving the security properties. Performing these operations on the protocol we enumerate the options available to a system.     

Identifying tampering operations in image operator chains based on decision fusion

There has been great interest in image forensics in recent years. However, most of the existing research focuses on detecting a certain tampering operation, which means that the introduced features usually depend on the investigated operation and only binary classification is considered. Given the case where the image tampering process involves diverse processing operations, we propose a decision fusion method for identifying tampering operations in operator chains in this work. The proposed method permits the integration of knowledge provided by available image forensic algorithms. Under this method, a similarity coefficient function is introduced to assign the weight of the output of each forensic classifier. Then, we utilize a combination rule based on local conflict management to merge these outputs. Comparison with the previous works shows an improvement in operations identification accuracy when an image has experienced multiple falsifications.     

对数数值系统的研究

对数数值系统(LNS)能够简化部分算术运算，从而能够提高运算效率以及降低系统功耗。文章从各个方面对LNS进行了详细的分析与讨论，主要包括LNS下数的表示、精度、范围以及LNS下数的运算，并且讨论了LNS数与普通浮点数之间的相互转换。同时对减小用于加减法运算中的查找表的大小提出了几点建议，最后针对LNS的低功耗问题做了简要的讨论。     

A Novel Reconfigurable Processor Using Dynamically Partitioned SIMD for Multimedia Applications

In this paper, we propose a novel reconfigurable processor using dynamically partitioned single‐instruction multiple‐data (DP‐SIMD) which is able to process multimedia data. The SIMD processor and parallel SIMD (P‐SIMD) processor, which is composed of a number of SIMD processors, are usually used these days. But these processors are inefficient because all processing units (PUs) should process the same operations all the time. Moreover, the PUs can process different operations only when every SIMD group operation is predefined. We propose a processor control method which can partition parallel processors into multiple SIMD‐based processors dynamically to enhance efficiency. For performance evaluation of the proposed method, we carried out the inverse transform, inverse quantization, and motion compensation operations of H.264 using processors based on SIMD, P‐SIMD, and DP‐SIMD. Experimental results show that the DP‐SIMD control method is more efficient than SIMD and P‐SIMD control methods by about 15% and 14%, respectively.     

An on-demand TV service architecture for networked home appliances

The recent advent of networked home appliances has enabled enhanced on-demand multimedia services to be feasible. Especially, personal video recorders have made it more convenient to manage broadcast TV programs at home by storing them on their own disks. However, standalone PVRs have limitations on availability of TV programs due to limited reception channel and storage capacity. Networked PVR services can get over these limitations by storing all broadcast TV programs in remote storage systems that servers provide. Thus, these networked PVR services can have several advantages over standalone PVRs in terms of cost and availability. In this article we therefore propose an on-demand TV service architecture for networked PVRs to reduce response times to interactive operations and save network bandwidth. Finally, we show from simulation results that our proposed architecture both decreases the number of programs whose initial time-shifting operations are delayed and increases the hit ratio in cache servers significantly.     

Fast Bit Gather, Bit Scatter and Bit Permutation Instructions for Commodity Microprocessors

Advanced bit manipulation operations are not efficiently supported by commodity word-oriented microprocessors. Programming tricks are typically devised to shorten the long sequence of instructions needed to emulate these complicated bit operations. As these bit manipulation operations are relevant to applications that are becoming increasingly important, we propose direct support for them in microprocessors. In particular, we propose fast bit gather (or parallel extract), bit scatter (or parallel deposit) and bit permutation instructions (including group, butterfly and inverse butterfly). We show that all these instructions can be implemented efficiently using both the fast butterfly and inverse butterfly network datapaths. Specifically, we show that parallel deposit can be mapped onto a butterfly circuit and parallel extract can be mapped onto an inverse butterfly circuit. We define static, dynamic and loop invariant versions of the instructions, with static versions utilizing a much simpler functional unit. We show how a hardware decoder can be implemented for the dynamic and loop-invariant versions to generate, dynamically, the control signals for the butterfly and inverse butterfly datapaths. The simplest functional unit we propose is smaller and faster than an ALU. We also show that these instructions yield significant speedups over a basic RISC architecture for a variety of different application kernels taken from applications domains including bioinformatics, steganography, coding, compression and random number generation.     

基于微过滤驱动的文件操作检测及重定向方法

研究了基于微过滤驱动的文件操作检测及重定向方法,旨在保护原系统文件的安全。微过滤驱动通过相应的过滤规则,对目标程序的文件操作进行监控,将创建、写入、删除等对系统文件安全有影响的操作重定向到指定的安全位置,以保护原系统文件的安全,同时记录这些操作。当检测完毕后,可根据记录文件进行分析,判断该程序是否执行了恶意的文件行为。     

On the symbol error rates for signal space diversity schemes over a rician fading channel

A signal space diversity (SSD) scheme is one of techniques to achieve diversity gain in fading channels. This method consists of two key operations: constellation rotation and component-wise interleaving. Because of these operations, the decision boundaries for the SSD are no longer perpendicular, and thus, different coordination approaches are required for the analysis of error rates compared to conventional rectangular coordinates. In this letter, we derive an exact expression of the symbol error rate for the SSD scheme in Rician fading channels with M-QAM and M-PSK. By defining the ratio of the standard deviation of the inphase and quadrature components, we introduce a new signal model for the SSD. Based on this signal model, we can compute the exact symbol error rate using polar coordinates. The computer simulation results confirm the accuracy of our analysis for fading channels.