各种多媒体终端系统

随着计算机为基础的多媒体通信和日益完善的多媒体时代的到来，日本电话电报公司研制了各种系统，及时地提供用户。本文介绍用于不同领域的各种多媒体系统。     

多媒体终端的组成应用与优点

计算机和数字技术的发展出现了有图形接口和多种应用程序的计算机。不仅买得起,而且没有信息技术知识的人也立即会用。ISDN(综合业务数据网)的引入,不仅可传输数据信息,并可传输质量满意的音频-视频技术。计算机,音频-视频设备和数字通信网络结合在一起,出现了前所未有的用途广泛的,具有友好用户接口的办公设备。不仅技术灵活,对用户更有裨益。     

个人通信多媒体终端

通信正在向信息传输量大、接续方便和传输距离远的方向发展，为了适应这一发展趋势，阿尔卡特公司正在开发一整套多媒体产品业务组合品，包括通信的各个环节，即基础结构、应用、终端和业务。     

诺基亚全力打造多媒体终端

2004年6月14日,诺基亚在新加坡和赫尔辛基同步举行年度“NokiaConnection”大会。会上,诺基亚推出了6630、6260、6170、2600、2650等五款手机,这五款手机的共同特点是:具有多媒体功能,设计精美,高度时尚化,视觉效果诱人。其中的6630可称为目前GSM市场上最先进的相机手机,其内置高达123万有效像素的数码相机,支持丰富的数码图像和MP3数字音乐播放器功能。在WCDMA网络中,诺基亚6630还支持高质量的实时流媒体和视频电话会议。此外,该手机还提供优化照片拍摄质量的连接式闪光灯、方便数据输入的无线蓝牙键盘,以及适用于车载环境的、可实现…     

多媒体终端在CATV中的应用

1 引 言 HFC有线电视网的基本功能是向用户传送广播电视信号,随着信息时代的来临,信息成为人类社会重要的资源,人们对信息的需求量不断增加且要求越来越高,希望尽可能方便、快捷地获得尽可能多的有用信息。目前各地有线电视网已分别开通了双向传输、视频点播、有线上网等交互式的多媒体业务,然而,HFC网中的上行噪声却始终未能解     

多媒体家庭终端——STB

本文介绍了日本ＮＥＣ公司研制的一种多媒体家庭终端－ＳＴＢ，它能够再生压缩编码数字数据（ＭＰＥＧ）并利用遥控器在图象用户接口（ＧＵＩ）屏幕上进行ＶＯＤ操作。     

多媒体终端在CATV中的应用

1　引言目前各地有线电视网已分别开通了双向传输、视频点播、有线上网等交互式的多媒体业务。然而 ,ＨＦＣ网中的上行噪声却始终未能解决。一般最佳设计为一个光节点接 5 0 0个用户 ,而有时用户数却远大于 5 0 0户 ,再加上进户后私装乱接现象十分严重 ,使得ＨＦＣ上行通道处于非常恶劣的噪声环境中。经分析 ,整个网络的噪声大约来自 3个方面 :①用户家中 ;②用户引入线 ;③固定的同轴设备 ,其中 ,70 %来自家中 ,2 5 %来自引入线 ,还有 5 %来自固定的同轴设备。也就是说 ,95 %的噪声来自用户盒之后。虽然目前的ＨＦＣ网络通过使用高通滤波器…     

带比特丢弃的AAL2分组话音复接器业务模型及性能分析

AAL2主要用于在ATM虚通路上有效传输话音、传真和话带数据,并可利用话音压缩技术和静默检测及消除技术来提高统计复用增益.本文分析了用服务速率随系统状态改变的M/D'/1/K泊松排队系统,为在输入端进行比特丢弃的AAL2分组话音复接器建立模型的缺陷,提出了话音分组到达率随系统状态改变的M'/D/1/K泊松排队模型,并进行了性能分析.计算机仿真证实作者提出的模型是合理的.     

全IP网络中的业务与终端

文章认为业务发展是网络发展的驱动力量,新技术只有在更多新业务面世的情况下才能得到大力发展.但如果业务终端的基础能力不足会形成较高的业务应用门槛,有时只有在终端技术实现突破后业务才会突飞猛进地发展.文章在分析业务发展中的终端与运营链之间的相互影响的基础上,探讨了移动网引入IMS架构后对终端制造商、网络运营商的影响,并明确指出下一代网络将归于IP网络、业务将驱动网络发展.     

多媒体通信终端发展趋向

本文讨论多媒体通信终端的发展趋向与通信规程进展。     

Securing RTP Packets Using Per‐Packet Key Exchange for Real‐Time Multimedia

For secure multimedia communications, existing encryption techniques use an online session key for the key exchange, for which key size is limited to less than 10 digits to accommodate the latency condition caused by user devices only being able to handle low computational loads. This condition results in poor security of recorded encrypted data. In this letter, we propose a packet key scheme that encrypts real‐time packets using a different key per packet for multimedia applications. Therefore, a key of a relatively small size can provide after‐transmission confidentiality to data of a real‐time session.     

PSTN网上可视多媒体通信终端

介绍了符合ＩＴＵ－ＴＨ．３２４协议的ＰＳＴＮ网上可视多媒体通信终端——ＫＤＭＭＴ。它在外接符合Ｖ．３４的调制解调器时,能通过ＰＳＴＮ网全双工实时传送图像和声音;介绍了终端系统的软硬件结构,高效实现音频和视频压缩编解码算法的关键技术以及系统互连时相关通信协议的设计与实现。     

基于双核处理器的无线多媒体终端设计

描述了如何利用TI OMAP芯片设计无线多媒体终端.在介绍了OMAP芯片的双核处理器结构后,阐述了该无线多媒体终端的硬件设计、软件设计,并给出两个示范性多媒体应用实例.测试证明,该终端具有高性能和低功耗的特点,能满足未来无线多媒体业务对手持设备的需求.     

Medium Access Control for Integrated Multimedia Wireless Access with the Use of a Video Packet Discard Scheme

A well designed Medium Access Control (MAC) protocol for wireless networks should provide an efficient mechanism to share the limited bandwidth resources, and satisfy the diverse and usually contradictory Quality of Service (QoS) requirements of each traffic class. In this paper a new MAC protocol for next generation wireless communications is presented and investigated. The protocol uses a combined Packet Discard/Forward Error Correction scheme in order to efficiently integrate MPEG-4 videoconference packet traffic with voice, SMS data and web packet traffic over a noisy wireless channel of high capacity. Our scheme achieves high aggregate channel throughput in all cases of traffic load, while preserving the Quality of Service (QoS) requirements of each traffic type, and is shown to clearly outperform DPRMA, another efficient MAC protocol proposed in the literature for multimedia traffic integration over wireless networks. Dr. Polychronis Koutsakis was born in Hania, Greece, in 1974. He received his 5-year Diploma in Electrical Engineering in 1997 from the University of Patras, Greece and his MSc and Ph.D. degrees in Electronic and Computer Engineering in 1999 and 2002, respectively, from the Technical University of Crete, Greece. He was a Visiting Lecturer at the Electronic and Computer Engineering Department of the same University for three years (2003–2006). He is currently an Assistant Professor at the Electrical and Computer Engineering Department of McMaster University, Canada. His research interests focus on the design, modeling and performance evaluation of computer communication networks, and especially on the design and evaluation of multiple access schemes for multimedia integration over wireless networks, on call admission control and traffic policing schemes for both wireless and wired networks, on multiple access control protocols for mobile satellite networks, wireless sensor networks and powerline networks, and on traffic modeling. Dr. Koutsakis has authored more than 45 peer-reviewed papers in the above mentioned areas, has served as a Guest Editor for an issue of the ACM Mobile Computing and Communications Review, as a TPC member for conferences such as IEEE GLOBECOM, IEEE LCN and IEEE PerCom, will serve as Session Chair for the IEEE GLOBECOM 2006 Symposium on Satellite & Space Communications and serves as a reviewer for most of the major journal publications focused on his research field. Moisis Vafiadis was born in Elefsina, Greece, in 1980. He has recently completed his studies towards the Diploma in Electronic Engineering at the Technological Educational Institute of Crete, Greece. His research interests focus on wireless personal communication networks, and especially on the MAC layer and on the development and testing of wireless multimedia applications.     

小波包分复用系统子载波的构造及调制实现

小波包分复用(WPDM)系统中作为子载波的小波包基函数必须是连续解析的,但实际中很难得到,通常需要对其进行逼近.通过滤波器系数采用迭代卷积的方法来对小波包基函数进行离散逼近,构造出的子载波满足小波包基函数的正交性.同时用此方法实现了多载波调制,并将该系统与正交频分复用(OFDM)系统在多径时延信道下进行了比较.仿真结果表明,WPDM系统在抑制ISI和ICI方面以及对定时偏差的影响上更具优势.     

Android平台智能移动终端的网络互连和多媒体资源共享

分析了移动终端智能入网机制及Android系统下的Wifi模块。设计了一种Android平台智能移动终端的联网和多媒体资源共享软件。具有该软件的Android平台的智能终端,可主动接入Wifi为底层的DLNA共享网络,并实现各智能终端之间的多媒体资源共享和服务拓展。     

Class-Based Packet Scheduling to Improve QoS for IP Video

An important issue for video transmission over IP networks is the preservation of perceived video quality despite packet loss. Packet loss can be detrimental to compressed video. However, reducing packet loss to a very low level is difficult with current techniques. Furthermore, even a very low objective loss probability can still seriously distort perceived video quality. This paper presents a packet scheduling scheme at a router which addresses the loss issues of networked video. Experiments using real video data show that the proposed scheme can significantly improve the visual quality of video and network efficiency. Moreover, it can provide different classes of videos with different levels of loss guarantees, while maintaining service fairness among the same class of videos.