衰落信道下两发送天线MIMO系统V-BLAST算法研究

对两发送天线MIMO系统在相关瑞利和莱斯信道下V—BLAST检测算法的性能进行了分析,推导出最优和固定检测两种方案中第一步和第二步的误码率．相对于独立同分布瑞利信道,考察了相关瑞利信道和莱斯信道对接收信噪比的影响;相对于固定检测方案,讨论了最优检测算法对信噪比的提升．理论分析和仿真结果表明,瑞利信道相关性或莱斯信道的直达波分量会减弱最优检测方案对信噪比的提升．     

802.11e EDCF信道接入机制的仿真研究

为进一步讨论EDCF(增强的分布式协调功能)数学建模的需要，对802．11DCF(分布式协调功能)和802．11e EDCF信道接入机制的性能进行了仿真分析，讨论了2种信道接人机制的差异，并探讨了EDCF提供QoS的原理，仿真结果表明，EDCF可以为无线局域网提供QoS保证，但在高优先级音频流和视频流过多的情况下，系统性能有所下降。     

基于IEEE802.11b协议的无线网络组建

介绍了基于IEEE802.11b协议的低成本双机互联无线网络的组建方法。基于该方法组建的双机无线网络成本低廉,同时实现计算机的文件共享、打印机共享和Internet连接共享。     

An Iterative Power Allocation Algorithm for Group-wise Space-Time Block Coding Systems

An iterative transmit power allocation (PA) algorithm was proposed for group-wise space-time block coding (G-STBC) systems with group-wise successive interference cancellation (GSIC) receivers. Group-wise interference suppression (GIS) filters are employed to separate each group's transmit signals from other interferences and noise. While the total power on all transmit symbols is constrained, all transmit PA coefficients are updated jointly according to the channel information at each iteration. Through PA, each detection symbol has the same post-detection signal to interference-and-noise ratio (SINR). The simulation results verify that the proposed PA algorithm converges at the equilibrium quickly after few iterations, and it achieves much lower bit error rates than the previous single symbol SIC PA and the fixed ratio PA algorithms for G-STBC systems with GSIC receivers .     

基于OPNET的分布式WLAN网络性能仿真研究

介绍了无线局域网的基本概念以及它的一些优缺点,分析了无线局域网中IEEE 802.11系列标准。基于网络仿真平台OPNET,构建了分布式无线局域网网络模型、节点模型和进程模型。为了优化网络性能,通过设置不同的网络参数(包括速率、信息包分组大小),对IEEE 802.11系列标准下的无线局域网网络性能进行了分析研究,减小了网络时延和丢包率,提高了系统吞吐量。对今后无线局域网部署中IEEE802.11系列标准的选择以及参数的设置有着重要的参考价值。     

Secure Authentication of WLAN Based on Elliptic Curve Cryptosystem

The security of wireless local area network (WLAN) becomes a bottleneck for its further applications. At present, many standard organizations and manufacturers of WLAN try to solve this problem. However, owing to the serious secure leak in IEEE802.11 standards, it is impossible to utterly solve the problem by simply adding some remedies. Based on the analysis on the security mechanism of WLAN and the latest techniques of WLAN security, a solution to WLAN security was presented. The solution makes preparation for the further combination of WLAN and Internet.     

Watermark in the digital video broadcasting handheld transmission signal

Transmitter identification (TxID) technique is used to diagnose the operation status of radio trans-mitters in DTV distributed transmission network. A new TxID method for digital video broadcasting-handheld (DVB-H) system is proposed. Watermark is embedded in the DVB-H signal to form the composite signal. Ac-cording to watermarking theory we demonstrate the required signal level for watermarking signal to achieve given bit error Probability under different circumstance. By selecting the reference pattern to generate watermarking signal, peak-to-average power ratio (PAPR) of the transmitted signal can be improved. Simulation results show that even in wireless situation the receiver can distinguish the watermarking signal with low embedding strength, and distortion to the host signal can also be ignored.     

A 1.5 bit/s Pipelined Analog-to-Digital Converter Design with Independency of Capacitor Mismatch

A new technique which is named charge temporary storage technique (CTST) was presented to improve the linearity of a 1.5 bit/s pipelined analog-to-digital converter (ADC). The residual voltage was obtained from the sampling capacitor, and the other capacitor was just a temporary storage of charge. Then, the linearity produced by the mismatch of these capacitors was eliminated without adding extra capacitor error-averaging amplifiers. The simulation results confirmed the high linearity and low dissipation of pipelined ADCs implemented in CTST, so CTST was a new method to implement high resolution, small size ADCs.     

基于Simulink的Turbo码系统仿真

在Turbo码编码、译码基本理论和结构的基础上,提出了一种用Simulink构建的Turbo码编、译码可控仿真模型,并在BPSK(binary phase-shift keying)调制的高斯白噪声信道(AWGN)中进行了系统建模和仿真实验.通过研究Turbo编码、卷积编码和无信道编码方案仿真系统的BER(bit error rate)性能,结果表明,所提出的Turbo编码的误码率优于其他2种方案1个数量级以上,尤低信噪比时更具优势.     

认知无线电网络MAC接入性能分析

认知无线电网络中授权用户享有频谱的优先使用权,一旦授权用户出现认知,用户必须中断正使用的频谱,造成正在传输的MAC帧丢失,认知无线电网络直接采用现有的IEEE802.11 DCF协议,无法解决由于中断引发的认知用户MAC帧丢失问题,当认知用户再次获得频谱接入机会时,将重新竞争接入,导致频谱切换延时较大.为解决该问题,本文改进了IEEE 802.11 DCF协议,提出增加冻结缓存机制,以此解决用户信道切换的延时较大问题.当无线链路出现中断时,改进的DCF协议通过冻结节点,中断当前计时器并缓存当前状态信息,认知用户和基站之间链路一旦恢复则继续传输中断前的MAC帧,从而避免了认知用户的重新竞争接入.仿真结果表明改进的DCF协议在频谱切换时能增大接入吞吐量,减小接入延时,提高了DCF机制在认知网络中的应用性能.     

CECNET—I型中华学习机辅助教学网络系统

本文介绍了以中华学习机为主机,并以 IBM PC/XT 为服务器的一种新型辅助教学网络系统。详述了其通道访问原理、体系结构、网络协议及实现技术。     

Dynamic wavelength and bandwidth allocation using adaptive linear prediction in WDM/TDM ethernet passive optical networks

Hybrid wavelength-division-multiplexing (WDM)/time-division-multiplexing (TDM) ethernet passive optical networks (EPONs) can achieve low per-subscriber cost and scalability to increase the number of subscribers. This paper discusses dynamic wavelength and bandwidth allocation (DWBA) algorithm in hybrid WDM/TDM EPONs. Based on the correlation structure of the variable bit rate (VBR) video traffic, we propose a quality-of-service (QoS) supported DWBA using adaptive linear traffic prediction. Wavelength and timeslot are allocated dynamically by optical line terminal (OLT) to all optical network units (ONUs) based on the bandwidth requests and the guaranteed service level agreements (SLA) of all ONUs. Mean square error of the predicted average arriv-ing rate of compound video traffic during waiting period is minimized through Wiener-Hopf equation. Simulation results show that the DWBA-adaptive-linear-prediction (DWBA-ALP) algorithm can significantly improve the QoS performances in terms of low delay and high bandwidth utilization.     

高校思政课与网络文化的人本互动

实现人的自由全面发展是马克思主义的核心思想．高校思政课作为对大学生进行思想政治教育的主渠道,其根本目标是实现人的自由全面发展,而网络文化的最终目标也是实现人的自由全面发展;以实现人的自由全面发展为切入点,有利于高校思政课与网络文化两者的人本互动,从而更有效地促进大学生自由而全面的发展．     

基于熵值加权逼近理想排序技术的城乡公交线网结构比较研究

为比较江苏南部和浙江北部两个典型发达地区的城乡公交线网结构，选择了海宁市、海盐县、张家港市和吴江区4 个县级行政区作为样本，借助Transcad 4.5 软件计算线网密度、非直线系 数、重复系数、连通度、站点覆盖率、平均站距等6 个城乡公交线网结构指标属性值并进行标准化，采用熵值加权逼近理想排序技术作为评价方法，通过利用评价指标固有信息来判别指标权重，计算城乡公交线网结构评价值与正、负理想解的距离后得到评价值与理想解的贴近度。对4 个样本的贴近度进行排序，发现张家港市城乡公交线网结构最佳，其后依次为吴江区、海宁市、海盐县，总的来说苏南样本优于浙北样本，两地城乡公交线网结构仍有改善空间。     

基于信息理论的交通信息量度量

针对语音信息缺乏量化和指路标志信息度量未反应实际出行条件下路网规模的影响作用问题,引入信息理论,构建语音信息量度量模型和图像信息量度量模型. 设计包含23组不同信息量的实验路网,测定不同信息量下的驾驶员反应时间. 研究结果显示:交通信息总量为52.22、57.90 bit时,出现反应时间的区域峰值;信息总量在50.74～57.38 bit区间段时,利于驾驶员对交通信息的认知且不产生信息量过载的现象;标志信息量为45.1、49.7 bit时,语音信息量位于5.12～10.24 bit区间利于降低驾驶员反应时间;语音信息量为5.12 bit时,标志信息位于49.70～54.30 bit区间利于提高驾驶员对交通状况认知.      

Bi-slotted binary tree algorithm with stack for radio frequency identification tag anti-collision

A radio frequency identification (RFID) reader will fail to identify tags if a collision occurs. This paper proposes a bi-slotted binary tree algorithm (BSBTA) with stack for RFID tag anti-collision to improve the performance of binary tree algorithm (BTA). In BSBTA, the reader detects collisions by Manchester code and stores colliding prefixes in a stack. The query is composed of a two-bit prefix and an index value. Following every reader query, there are two timeslots for tags whose pointers and identities (IDs) match the query to respond, one for the tag whose next bit is 0 and the other for the tag with 1 as its next bit. Performance analysis and evaluation are also given. The time complexity and the communication complexity of BTA and BSBTA are derived. The simulation results compare the performance of BSBTA with several related anti-collision algorithms. It is shown that BSBTA outperforms BTA in terms of the average number of responded bits and timeslots for one tag identification.     

基于ICA的MIMO系统空时盲均衡算法

多输入多输出系统的MMSE均衡中,由于接收端采样大小的限制,对观测信号协方差矩阵的估计和信道的盲辨识误差会严重影响均衡性能,采用独立分量分析作为一种辅助手段改进传统的均衡器,并选择最佳均衡时延优化算法。仿真结果表明,该算法提高了传统算法的鲁棒性,在大大降低计算复杂度的同时改善了均衡性能。     

A Reliable Adaptive High-Definition Transmission System for Distance Learning

There is an increasing demand for supporting high-quality real-time audiovisual services for the next generation wired and wireless networks. However, due to variety of bandwidths of different networks, it is a great challenge for deployment. In this paper, a novel high-definition (HD) video transmission system was proposed which depends upon reliable compound multicast protocols and QoS control over the various kinds of networks. This system detects client's network condition and assigns it to a proper proxy. Each proxy is capable of detecting network parameters and adaptively tuning such transport parameters as bit rate, video resolution, frame rate and QoS mechanisms to this condition. It also provides FEC error recovery under consideration of characteristics of MPEG4 video codec. Our simulation demonstrates that different network clients such as ADSL, CERNET, and CERNET2 can receive more video reliability with less delay.     

基于RTP/RTCP的音视频WiFi传输系统的设计

本系统设计了一个无线WiFi音视频传输方案,可用于视频监控,视频教学,旅游导游等领域.系统采用i.MX27多媒体处理器,WiFi模块采用基于IEEE802.11b的无线协议,流媒体传输采用RTP/RTCP协议,视频的编解码采用成熟的MPEG4标准,实现基于2.4GHz无线网络传输的音频流和视频流数据的传输.实现了音视频的WiFi传输,在接收端音视频还原流畅.     

The Implementation of Mirror-Image Effect in MPEG-2 Compressed Video

Straightforward techniques for spatial domain digital video editing (DVE) of compressed video via decompression and recompression are computationally expensive. In this paper, a novel algorithm was proposed for mirror-image special effect editing in compressed video without full frame decompression and motion estimation.The results show that with the reducing of computational complexity, the quality of edited video in compressed domain is still close to the quality of the edited video in uncompressed domain at the same bit rate.