多描述视频编码方法研究

稳健的视频编码压缩方法是实时网络视频传输的关键，多描述视频编码可为解决不可靠信道视频传输的丢包、误码和延时等所带来的视频质量严重降质问题提供一种新途径。本文介绍了面向网络传输的多描述视频编码的研究现状和一些典型的多描述视频编码器，并对其中的关键技术进行了分析、讨论。     

Wireless communications in the twenty-first century: a perspective

Wireless communications are expected to be the dominant mode of access technology in the next century. Besides voice, a new range of services such as multimedia, high-speed data, etc. are being offered for delivery over wireless networks. Mobility will be seamless, realizing the concept of persons being in contact anywhere, at any time. Two developments are likely to have a substantial impact on the mobile communications systems deployed in the twenty-first century: the adoption of International Mobile Telecommunications-2000 and wireless asynchronous transfer mode (ATM). They are two different but cooperative approaches to providing high-speed wireless access. The limitations of the radio-frequency spectrum and radio channel propagation impose special constraints on the technologies of systems to be deployed. To make future mobile systems globally acceptable, standardization efforts are underway in the International Telecommunications Union and the ATM Forum. This paper reviews the international standardization efforts, the challenges to the technologies imposed by the radio spectrum limitations, radio channel propagation-induced distortions, and possible solutions. Evolution, migration, and architecture issues also are discussed     

综合信息传输平台技术探讨

科学考察船的特殊性要求对通信业务的综合集成。阐述了科学考察船各类通信业务的需求和传输特点,提出了通信业务在综合信息传输平台的集成及业务交换原理和实现方法,主要描述了程控业务和视频业务嵌入的技术,重点解决了程控业务中的信令传输、语音交换和视频数据流封装等关键技术。综合业务传输平台的运用同时解决了多种业务综合传输的稳定性和可靠性,为科学考察船的通信保障发挥了重要作用。     

Enhanced Communications in an Executive Office

Bell Laboratories executives are "subjects" in a trial to study how people might take advantage of communications services made possible by advancing technologies. An experimental teleterminal integrates voice and data communications to deliver the services under study: enhanced calling, electronic messaging, information and news retrieval, and calendaring. These enhanced communications services and the trial results are described, with emphasis on human factors and office sociology.     

Speech and language processing for next-millennium communicationsservices

In the future, the world of telecommunications will be vastly different than it is today. The driving force will be the seamless integration of real time communications (e.g. voice, video, music, etc.) and data into a single network, with ubiquitous access to that network anywhere, anytime, and by a wide range of devices. The only currently available ubiquitous access device to the network is the telephone, and the only ubiquitous user access technology mode is spoken voice commands and natural language dialogues with machines. In the future, new access devices and modes will augment speech in this role, but are unlikely to supplant the telephone and access by speech anytime soon. Speech technologies have progressed to the point where they are now viable for a broad range of communications services, including: compression of speech for use over wired and wireless networks; speech synthesis, recognition, and understanding for dialogue access to information, people, and messaging; and speaker verification for secure access to information and services. The paper provides brief overviews of these technologies, discusses some of the unique properties of wireless, plain old telephone service, and Internet protocol networks that make voice communication and control problematic, and describes the types of voice services available in the past and today, and those that we foresee becoming available over the next several years     

Wireless mobile communications at the start of the 21st century

At the start of the 21st century, the wireless mobile markets are witnessing unprecedented growth fueled by an information explosion and a technology revolution. In the radio frequency arena, the trend is to move from narrowband to wideband with a family of standards tailored to a variety of application needs. Many enabling technologies including wideband code-division multiple access, software-defined radio, intelligent antennas, and digital processing devices are greatly improving the spectral efficiency of third-generation systems. In the mobile network area, the trend is to move from traditional circuit-switched systems to packet-switched programmable networks that integrate both voice and packet services, and eventually evolve toward an all-IP network. Furthermore, accompanied by wireless mobile location technology, wireless mobile Internet is expected to revolutionize the services that can be provided to consumers in the right place and at the right time. Wireless mobile communications may not only complement the well established wireline network; it may also become a serious competitor in years to come. We review the history of the wireless mobile communications, examine the current progress in standards and technologies, and discuss possible trends for wireless mobile solutions     

Handling multimedia information with VLSI

Identifies the basic technological components of multimedia communications. Among these technologies, multimedia processing and transmission already benefit heavily from VLSI advances. in fact, these two technologies could not have matured without special-purpose VLSI chips. We have examined basic processing required in these technologies and some VLSI architectures. The focus has been on standard-compliant VLSI chips, because the eventual goal of communications is to allow everyone to reach others without constraints. There are still a number of evolving standards, which means that we might witness yet another wave of VLSI chips for multimedia communications     

QoS enabled voice support in the next generation Internet: issues,existing approaches and challenges

The Internet is under rapid growth and continuous evolution in order to accommodate an increasingly large number of applications with diverse service requirements. In particular, Internet telephony, or voice over IP is one of the most promising services currently being deployed. Besides the potentially significant cost reduction, Internet telephony can offer many new features and easier integration with widely adopted Web-based services. Despite these advantages, there still exist a number of barriers to the widespread deployment of Internet telephony. The most prominent one, however, is how to ensure the QoS needed for voice conversation. The purpose of this article is to survey the state-of-the-art technologies in enabling the QoS support for voice communications in the next-generation Internet. In this article, we first review the existing technologies in supporting voice over IP networks, including the basic mechanisms in the IETF Internet telephony architecture and ITU-T H.323-related Recommendations. We then discuss the IETF QoS framework, specifically the Intserv and Diffserv framework. Finally, we present two leading companies' (Cisco and Lucent) solutions to offering IP telephony services as examples to illustrate how real systems are implemented     

安全网络视频会议系统的设计

为网络视频会议传输提供有效的通信安全,采用一个会议密钥分配的智能卡系统,来解决使用者身份认证和通信安全问题.在语音和图像方面,分别采用GSM6.10语音压缩和JPEG图像压缩来降低数据量.在智能卡系统内引入多种对称式加密算法以供使用者选择,在多人与会的环境下,利用该智能卡系统来分配一个共同的会议密钥,让与会者可经由这个共同的会议密钥来对资料作加密保护及数字签名.     

Digital video coding standards and their role in videocommunications

The efficient digital representation of image and video signals has been subject of considerable research over the past 20 years. With the growing availability of digital transmission links, progress in signal processing, VLSI technology and image compression research, visual communications has become more feasible than ever. Digital video coding technology has developed into a mature field and a diversity of products has been developed-targeted for a wide range of emerging applications, such as video on demand, digital TV/HDTV broadcasting, and multimedia image/video database services. With the increased commercial interest in video communications the need for international image and video coding standards arose. Standardization of video coding algorithms holds the promise of large markets for video communication equipment. Interoperability of implementations from different vendors enables the consumer to access video from a wider range of services and VLSI implementations of coding algorithms conforming to international standards can be manufactured at considerably reduced costs. The purpose of this paper is to provide an overview of today's image and video coding standards and their role in video communications. The different coding algorithms developed for each standard are reviewed and the commonalities between the standards are discussed     

Evolving public safety communication systems by integrating WLAN and TETRA networks

This article contributes to the evolution of public safety communication systems by specifying a novel solution for integrating WLAN and Terrestrial Trunked Radio (TETRA) networks. The specified solution allows TETRA terminals to interface to the TETRA Switching and Management Infrastructure (SwMI) over a broadband WLAN radio access network, instead of the conventional narrowband TETRA radio network. These terminals are fully interoperable with conventional TETRA terminals and can employ all TETRA services, including group calls, short data messaging, packet data, and so forth. In addition, however, such terminals can support a range of brand new capabilities enabled by the WLAN, such as broadband data services, true concurrent voice and data services, simultaneous reception of many group calls, reduced call setup and voice transmission delays, improved voice quality, and so forth. The specified solution is solely based on IP multicast and Voice-over-IP (VoIP) technologies and thus fits ideally to the all-IP architecture being introduced by the MESA project for the next generation of public safety and disaster relief communication systems.     

数据管理中心的原理及应用

在通信行业融合发展的趋势下,人们对通信的要求已不仅限于单一的语音信息交流,更青睐于个性化的综合信息服务,固定与移动的融合,语音、视频和数据的融合等等。这些融合给电信业务带来了深刻变革。要实现新业务的统一规划就需要采用数据管理中心实现数据的集中管理。基于数据管理中心的实现原理,通过业务与控制相分离,能够给用户提供更多更快捷的增值业务,提高业务增长点。     

Telecommunications at the Nagano 1998 Winter Olympic Games

The Olympic Games pose a big challenge for all telecommunications services, including voice communications, live video transmission, data transmission, and cellular phone services. Even though it is only a 16-day program, the Olympics require a large-capacity network and special grade quality and reliability over a wide geographical area (including ski resorts in the mountains). This article presents an overview of the telecommunications systems used in the Nagano 1998 Winter Olympic Games and reviews their performance     

3G wireless and cdma2000 1/spl times/ evolution in Korea

The cdma2000/spl reg/ I/spl times/EV-DV system is designed to meet the ever-increasing demand for high-speed packet data transmission while providing the same level of revenue generated by conventional voice communications on existing cdma2000 1/spl times/ systems. It supports concurrent voice and high-speed data on a single cdma 1.25 MHz carrier, and offers improved flexibility for operators to manage data and voice services cost efficiently. However, the Korean market has proved that providing higher bandwidth to the user does not guarantee the success of mobile data service. Users tend not to use expensive mobile wireless data services such as video streaming, video on demand, and MP3 music download service that they feel do not provide enough justification for their costs. The problem LG Telecom faces now as a mobile operator is not only to evolve technologies that enable various services, but also to find a way to provide attractive services at reasonable prices. This article describes experiences in the wireless data market in Korea as well as the market needs and driving forces for cdma2000 1/spl times/EV-DV developments.     

An efficient traffic control scheme for store‐and‐forward video‐on‐demand services

According to the MPEG‐1/2 standard, full motion video can be compressed and stored in an information warehouse. Multiplexing with normal voice calls, it is retrieved and delivered to the customer's local BISDN central office via 155 Mb/s trunks. These voice calls have higher priority than video‐on‐demand (VOD) so that normal voice services will not be influenced by VOD transmission. The number of voice calls always fluctuates in real‐time. Thus, an efficient traffic control scheme is highly desired to guarantee a given level of performance and achieve as great as possible use of available bandwidth. Based on the fact that the number of real‐time voice calls is variable, and the use of available capacity is less than 100 per cent, this paper will present an efficient traffic control scheme for store‐and‐forward VOD services, and demonstrate the scheme by various simulation results. Copyright © 2001 John Wiley & Sons, Ltd.     

Satellite telenets: A techno-economic assessment of major trends for the future

This paper reviews the historical trends in the development of new communications satellite technology and the technical and economic forces that will drive a new revolution in wide-band communications services in the 1980s and 1990s. The following key technical and service aspects of the new satellite telenets of the 1980s and 1990s will be addressed: new digital services, new antenna designs, intersatellite links, on-board signal processing and regeneration, and new architectural and servicing concepts for long-lived satellites. The possibility of non-Clarke orbit communications satellites in the 21st century will also be reviewed. Competitive technical and economic trends in other forms of telecommunications technologies will also be explored, in order to establish some economic and service "figures of merit" for the future. This analysis reveals some exciting and unexpected aspects about the new satellite telenets of the late-twentieth and early-twenty- first centuries. If messages are beamed to and from communications satellites by laser, there would be room for so many channels that every person on Earth could have his own, just as he has his own telephone number. He could reach everyone on Earth with no trouble, transmitting sight as well as sound... It is not unlikely that a good beginning toward laser satellite communications may be made by the end of the century... If so, it will represent a remarkable advance, considering that at the beginning of the century, mankind was still tied to the wire. (Isaac Asimov, Science Past, Science Present. New York: Ace Books, 1975.) If you're willing to spend enough money on advanced electronics you can virtually guarantee they can be made to not work.--One of Augustine's Laws. ("Augustine's Laws and major systems development programs, pt. 2," Aeronautics and Astronautics, p. 49, Jan. 1981.)     

Novel satellite digital video TDMA system for business videocommunications

The authors propose a satellite video signal transmission system that uses a time division multiple access (TDMA) scheme for digital video signal transmission and a code division multiple access (CDMA) scheme for voice signal transmission from a video signal reception-only earth station (backward voice signal transmission). The adoption of a TDMA scheme makes it possible to transmit video signals from various places and to communicate in multipoint-to-(multi)point mode. For backward voice channel transmission from video signal reception-only earth stations, a superposed CDMA voice signal transmission over TDMA video signals by using the same transponder is proposed. The employment of high coding gain forward error correction and development of a cochannel interference cancellation technique have made it possible for the proposed system to transmit a practical number of voice channels. The performance of the proposed system has been experimentally evaluated and the results show the proposed scheme can transmit about 20 CDMA voice channels simultaneously     

From here to ATM

While not optimum for any one type of traffic, asynchronous transfer mode is clearly the best compromise between the conflicting needs of data, voice, and video. The most interesting question is not whether ATM will take over the data communications highway, but how it will be phased in. The author describes how anticipating how wide- and local-area networks will shift into asynchronous transfer mode requires a grasp of today's technologies     

迈向21世纪的无线通信技术

无线电通信是下一个世纪的主要接入技术,无线网络了除了提供语音服务之外,还提供多媒体和高速数据业务。本文介绍了第３代国际移动通信系统ＩＭＴ－２０００和无线异步转移模式（ＷＡＴＭ）的概念,对它们的关键技术进行了总结,并对其发展方向作了进一步的展望。     

基于小波变换的极低码率视频编码技术

介绍几种基于小波的极低码率视频编码及其应用，在世纪之替之际出现了许多新颖和特殊需求的应用领域，例如会议电视，移动通信中的视频传输等等。这些应用的出现，为极低码率的视频编码研究重新注入了新的动力。