Technical issues regarding satellite packet switching

Many concepts for advanced communication satellite networks have recently been proposed. Critical technical issues relating to satellite packet switching for meshed very small aperture terminal networks and broadband networks are addressed. Hardware considerations, networking and testing issues are discussed.     

话音VSAT系统突发话音帧的帧处理

本文在简介话音VSAT系统的基础上,分析了在VSAT系统中应用的一类突发话音帧的帧结构;针对突发帧的特点,提出了一种全软件的帧处理方法,给出了性能分析,并在TMS320E17上实现。经过理论分析和实用证明,此方法简单,性能优越。     

VSAT上变频器的杂散,互调干扰分析与电路的优化设计

为保证卫星通信VSAT系统内和系统间良好的电磁兼容性，必须严格限制带外和寄生辐射．本文分析了VSAT上变频器来散、互调干扰等的主要来源，包括信频与本振谐波组合干扰分量，多载波之间的互调分量等。在此基础上提出了旨在减小杂散电平的电路优化设计方法，其中包括在满足上变额总增益要求的条件下，电路各级增益或衰减的配置、本振功率的确定等，最后给出应用实例。     

A simple key agreement scheme based on chaotic maps for VSAT satellite communications

Security is an essential requirement in any data communication system because a cyber criminal might try to break into it at any point by any means possible. A key agreement procedure is a necessary technique to ensure the security of data communication by way of encryption and mutual authentication. This article proposes a simple key agreement scheme on the basis of chaotic maps for VSAT satellite communications. The new scheme keeps the advantages of all chaotic maps‐based public key cryptosystems, providing a secure function of session key agreement. Based on the intractability of chaotic map discrete logarithm problem and chaotic map Diffie–Hellman problem, the security of this new scheme has been proven to be robust enough against all the well‐known cryptographical attacks with perfect forward secrecy provided. In addition, compared with similar schemes that serve the same purposes, the proposed scheme demands a lower computation cost. With all the previous features put together, the proposed scheme is extremely suitable for the use in very small aperture terminal satellite communication environments. Copyright © 2013 John Wiley & Sons, Ltd.     

全国党校系统卫星远程教学网的构建及应用

随着信息社会的飞速发展,卫星远程教学作为一种独具特色的远程教育方式,已经成为创建学习型社会,素质教育及干部教育进程中无法取代的重要手段.为推动全国党校系统的教学工作.实现全国党校系统的交互远程教学,卫星远程教学发挥重要作用.     

Some methodological deficiencies in studies on traffic accident predictors

The paper discusses some methodological problems in (psychological) research on traffic accident predictors and reviews a convenience sample of the literature. Three methodological aspects are identified as being important: reliability of accident predictors, time period for accidents used as dependent variable, and culpability for accidents. Papers are scrutinized and most are found to be wanting in these aspects. Traffic researchers do not adhere to, or hardly even discuss, these basic methodological problems. It is concluded that the current research into (psychological) accident predictors is fraught with methodological deficiencies. Why most studies seem to be deficient in these aspects is not clear, as several researchers have pointed out these problems.     

宽带VSAT网络中的多址技术

多址技术是宽带VSAT网络中的关键技术，先分析讨论了目前宽带卫星网络中提出的多种多址技术，业务使用的多址方式．它对用户的QoS要求和卫星信道的利用率都有重要的影响．文中首指出它们各自在应用中可能存在的问题：然后具体分析了ATM各类     

Engineering costs proxy models for China rural access network and its application

The article builds three engineering rural access network models that describe the structure of network elements and their relative engineering parameters for cable access、synchronous code division multiple access (SCDMA), and very small aperture terminal (VSAT) access technologies in the rural areas of China. Of the three access technologies, cable access and SCDMA access are the most popular access technologies. Besides, there still exist some remote special areas such as western mountain areas, whose natural environment is so bad that VSAT becomes the unique economical access way. Fully considering rural areas' geographical environments' impact, the article introduces geographical revised factor (GRF) to the models. By substituting the network data from the operators into the models, the article obtains the integrated networking values and does further researches on different access networks.     

VSAT卫星通信网及其发展趋势

本文介绍VSAT卫星通信网的组成、特点和各种多址方式,预测其技术发展趋势。     

Synchronization of voice data on asynchronous networks and its implementation for a VSAT channel gateway

The variation of packet‐arrival intervals is one of the problems to be solved in realizing real‐time voice communications on asynchronous networks such as the Internet. Although the variation can be absorbed by a receiving buffer, the end‐to‐end delay increases in proportion to the amount of buffered data. Therefore, the guideline for the receiving buffer's design that considers the trade‐off between voice quality and delay is needed. In this paper, the design of the receiving buffer by means of the voice‐speed‐conversion technique is discussed. According to our scenario, the buffer size was expected to be equivalent to the time length in which the probability distribution function of the packet‐arrival intervals was about 95% to 99%. However, it is shown that synchronized voice reproduction can be achieved within a preset delay, which is shorter than the corresponding time to the buffer size. This is achieved by keeping the rate of voice speed conversion within the range of 50% to 150% depending on the variation of the intervals. The proposed method was implemented in the conventional UNIX workstations (WSs) connected to an Ethernet segment. The average voice delay between WSs was 150 to 180 ms and the synchronized voice reproduction was achieved with a standard deviation of 13 to 25 ms. The proposed method is applied to VSAT‐satellite‐channel gateways to realize the real‐time voice communication between the WSs through a VSAT channel. © 1999 Scripta Technica, Electr Eng Jpn, 130(2): 68–79, 2000