Scheduling Algorithms for Packet-Oriented MAC Protocols in Wireless Multimedia Systems

Future generation wireless multimediacommunications will require efficient Medium AccessControl (MAC) protocols able to guarantee suitable Qualityof Service (QoS) levels for different traffic classes whileachieving a high utilization of radio resources. This paperproposes a new scheduling technique to be adopted at the MAClevel in wireless access systems, named Dynamic Scheduling-Time DivisionDuplexing (DS-TDD), that efficiently managesvideo, voice, Web and background traffics. A theoretical approachis proposed in this paper to evaluate the DS-TDD performance withvoice and Web traffics. Simulation results have permitted tohighlight the following promising characteristics of the DS-TDDscheme: (i) a high capacity of real-time traffics isattained with a QoS insensitive to Web and background trafficloads; (ii) a high throughput can be guaranteed whilepreserving the QoS levels of the different traffic classes;(iii) heavier downlink traffic loads do not modify the QoSof uplink traffics. Finally, extensive comparisons with differentscheduling schemes proposed in the literature have permitted tohighlight the better performanceof DS-TDD.     

A Neural Network Approach for Signal Detection in Digital Communications

In this paper, we propose a new approach for signal detection in wireless digital communications based on the neural network with transient chaos and time-varying gain (NNTCTG), and give a concrete model of the signal detector after appropriate transformations and mappings. It is well known that the problem of the maximum likelihood signal detection can be described as a complex optimization problem that has so many local optima that conventional Hopfield-type neural networks fail to solve. By refraining from the serious local optima problem of Hopfield-type neural networks, the NNTCTG makes use of the time-varying parameters of the recurrent neural network to control the evolving behavior of the network so that the network undergoes the transition from chaotic behavior to gradient convergence. It has richer and more flexible dynamics rather than conventional neural networks only with point attractors, so that it can be expected to have much ability to search for globally optimal or near-optimal solutions. After going through a transiently inverse-bifurcation process, the NNTCTG can approach the global optimum or the neighborhood of global optimum of our problem. Simulation experiments have been performed to show the effectiveness and validation of the proposed neural network based method for the signal detection in digital communications.     

移动IP综述

论述了移动IP的概念和发展过程，分析了国内外对移动IP研究的重点问题及其方法，对移动IP的发展方向进行了归纳和总结，并提出了有关用的问题。     

VC++实现的串口通讯数据处理

说明了在异步串行通信(RS-232)的工作方式下,对所接收的数据进行接收、处理,丢弃乱码,并进行保存的可靠方法,并给出了相关的VC 语言程序.     

The Minimum PAPR Code for OFDM Systems

In this letter, a block code that minimizes the peak‐to‐average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals is proposed. It is shown that peak envelope power is invariant to cyclic shift and codeword inversion. The systematic encoding rule for the proposed code is composed of searching for a seed codeword, shifting the register elements, and determining codeword inversion. This eliminates the look‐up table for one‐to‐one correspondence between the source and the coded data. Computer simulation confirms that OFDM systems with the proposed code always have the minimum PAPR.     

美籍华裔专家讲通信工程技术新动态

本文扼要介绍１９９５年北京中美工程技术研讨会通信组五位美籍华裔专家关于通信技术新动态的专题报告。一是宽带综合业务数字网的同步数字系列（ＳＤＨ）和异步转移模式（ＡＴＭ）；二是光纤通信系统的光放大器（ＯＦＡ）、波分多路（ＷＤＭ）、光电子集成（ＯＥＩＣ）、色散补偿和新型光纤；三是蜂窝网车载移动通信和全国性个人通信业务（ＰＣＳ）、时分多址（ＴＤＭＡ）和码分多址（ＣＤＭＡ），四是智能网（ＩＮ）体系结构、概念模型和业务管理系统（ＳＭＳ）；五是数字传输网的恢复（ＦＡＳＴＡＲ）、维护（ＴＭＰ）和供应（ＴＳＮＯＷ）三种管理平台，及综合网络管理系统（ＩＮＭＳ）。     

不断进取的AXE10

有近２０年历史的爱立信ＡＸＥ１０交换机在信息时代到来之际再放异彩，目前，它作为公共平台广泛应用于ＰＳＴＮ、ＩＳＤＮ、ＩＮ，ＰＬＭＮ、信令网和商务通信等。     

中国光纤通信技术的研究、应用和发展

主要从光纤光缆、光器件与组件、光传输设备与系统、光网络建设等方面论述光纤通信技术在我国的研究、应用发展历程，并对我国光纤通信技术的未来发展进行展望。     

蜂窝移动通信系统核心网络的演进与全IP核心网络

分析了现有移动通信网络存在的问题，阐述了第2代移动通信核心网向第3代移动通信核心网演进的必然性：讨论了第2代移动通信核心网向第3代移动通信核心网演进所采用的演进策略，介绍了两种可供选择的全IP核心网络的参考结构。     

星间激光通信技术进展与趋势

较详细地评述了目前国外卫星间光通信技术研究的现状．根据关键单元技术的进展情况，总结了未来星间光通信系统的发展趋势。