小型SDH光纤通信环网的同步和保护

通过对常见的SDH网同步方式和保护方式的分析，介绍了小型SDH光纤通信网应选择的同步方式和保护方式。     

红外通信在电力抄表系统中的应用

红外通信是一种价格低廉、适应范围比较广的短距离无线通信技术。本文给出了红外通信在电力抄表系统中的应用实例     

环球移动通信系统(GSM)的研究

介绍了环球移动通信系统 (GSM)的原理 ,并着重讨论了三种多址方式的异同 .     

有限元法分析非对称光纤耦合器波导

用有限元法分析了非对称光纤耦合器波导的场特性.利用自适应法划分有限元三角形格子,计算出在不同结构下最低阶的4个模式的传播常数.数值结果表明,组成耦合器的光纤半径比对偶模和奇模的传播常数都有明显的影响.与奇模不同的是,偶模传播常数对两光纤熔融程度不敏感.     

3G及后3G时代的无线数据通信研究

该文研究了3G及后3G时代无线数据通信的背景、现状和发展趋势。论述了第三代移动通信(3G)、无线局域网(WLAN)、无线个人域网(WPAN)、蓝牙(BLUETOOTH)和第四代移动通信(4G)的概念与特点,讨论了其中的一些热点问题,说明了多媒体内容、互连网和无线移动终端是无线数据通信发展的驱动力。     

Sharing Multicast Videos Using Patching Streams

The access patterns of most information systems follow the 80/20 rules. That is, 80% of the requests are for 20% of the data. A video server can take advantage of this property by waiting for requests and serving them together in one multicast. This simple strategy, however, incurs service delay. We address this drawback in this paper by allowing clients to receive the leading portion of a video on demand, and the rest of the video from an ongoing multicast. Since clients do not have to wait for the next multicast, the service latency is essentially zero. Furthermore, since most services require the server to deliver only a small leading portion of the video, the server can serve many more clients per time unit. We analyze the performance of this approach, and determine the optimal condition for when to use this strategy. We compare its performance to a hardware solution called Piggybacking. The results indicate that more than 200% improvement is achievable.     

基于TCP/IP和Socket实现网络通信

对TCP／IP协议核心与应用程序的关系进行了分析，提出了利用Windows Sockets套接字编程的一般方法。在此基础上解决了基于TCP／IP协议下的网络通信问题，能够准确方便地在服务器和客户端实时收发文件和互相通信，并给出了部分源程序。     

影响空地激光通信链路通信时段选择方案的背景光及大气湍流效应因素

对空地激光通信链路通信时段选择与背景光、大气湍流效应的关系进行了理论分析、仿真及实验研究 ,指出了空地激光通信链路通信时段选择方案一般应遵循的原则 :1)由于夜晚时段大气湍流强度较弱 ,空地激光通信可多选择夜晚时段 ;2 )晴天天气条件下 ,空地激光通信应避免在太阳光强烈的中午时段建立通信 ,建议多使用清晨和下午时段 3 )阴天天气条件下 ,背景光和大气湍流效应对空地激光通信链路的影响较小 ,因此只要链路通信光能量能满足链路功率分配指标要求 ,空地激光通信链路适合在阴天天气条件下进行     

Influence of imperfect carrier recovery on satellite QPSK communication system performance

The purpose of this paper is to provide the theoretical approach for determining the bit error probability in detecting a coherent quaternary phase-shift-keyed signal transmitted over a soft-limited channel in the presence of the uplink and downlink noise, as well as the noisy carrier reference signal. The uplink noise is considered in the specific way through the envelope variations and the frequency offset of the signal remitted by the satellite station having influence on the variations of the phase-locked loop parameters in the receiving ground station, consequently on the probability density function of the phase error, i.e. the average bit error probability. The downlink noise is also taken into consideration. The determined results are based on the non-linear phase-locked loop model with primary emphasis on the degradations in the system performance produced by the imperfect carrier signal extraction. Copyright © 1999 John Wiley & Sons, Ltd.     

迎接百家争鸣的移动增值业务时代

移动短信业务深受广大用户的欢迎,发展异常火爆．创造了丰厚的经济效益。但移动短信业务奇迹般增长的同时也应看到,一个首经创造了增长奇迹的业务在2004年却放慢了发展步伐,其原因是多方面的：既有语音业务和即时通信的替代作用．又有短信业务市场监管力度的加强等外在原因．也有增值业务创新不足,短信业务存在发展瓶颈等内在原因。未来业务将向多样化、简便化、娱乐化、精确化和多元化方向发展。