Inmarsat expands its horizons

The International Maritime Satellite Organization (INMARSAT) is the world's only commercial satellite system providing mobile communications. This article describes the system and the services which are provided through it to the worldwide shipping and offshore industries. It provides some background on the establishment of the system and why maritime nations looked to satellites as the way to effect a dramatic improvement in maritime communications. The article discusses some of the research and development now being carried out which is expected to lead to the provision of new services, including aeronautical communications via satellite. Also mentioned is the role to be played by INMARSAT in the Future Global Maritime Distress and Safety System, now being developed by the International Maritime Organization for introduction in 1990. New services, such as these, and greatly expanded capacity are to be provided by INMARSAT in its second generation system, consisting of a new series of satellites for launch from 1988.     

海事卫星BGAN载波恢复技术研究

载波恢复是实现信号相干解调的一个必不可少的部分。通过研究海事卫星全球宽带网（BGAN）信号帧中的独特字（UW）,采用数据辅助的频偏估计和面向判决的相偏估计算法,完成了对实际接收海事卫星BGAN信号的载波恢复,该方法捕获时间快,估计范围大,准确度高。结果表明该算法对BGAN信号的频偏、相偏均能正确收敛,恢复后星座图接近16QAM星座图,为信号解调提供保证。     

Multimedia services and data broadcasting via satellite

Since 1995 EUTELSAT, as well as other service providers (in Europe and worldwide), in collaboration with industrial partners and research institutions have been developing digital platforms for providing multimedia services as well as data broadcasting via satellite services. These digital platforms are based on the same technologies as those used for the emerging digital television and radio services, namely Digital Video Broadcasting (DVB) and MPEG-2. These platforms will greatly improve the speed of multimedia services to the end user (e.g. up to 2 Mbit/s per session on an Internet connection) and will provide the possibility of downloading very large files in a very short time (e.g. downloading speeds of up to 40 Mbit/s per transponder) to a very large number of customers. By using the same technology as for digital television and radio, large economies of scale are foreseen, thus making these digital platforms very affordable on both the unlink side and the receiver side (e.g. less than $300 for the DVB-PC card kit)     

基于高速网络技术的多媒体网络设计

本文介绍了多媒体网络、高速网络以及交换技术，运用交换技术及快速以太网设计出适用于不同规模用户的优化的多媒体网络方案，同时也提供了上述网络方案向ＡＴＭ过渡的方法，另外还指出了传统的太网改造升级的基本思路。     

Multimedia annotation via semi-supervised shared-subspace feature selection

With the rapid development of social network and computer technologies, we always confront with high-dimensional multimedia data. It is time-consuming and unrealistic to organize such a large amount of data. Most existing methods are not appropriate for large-scale data due to their dependence of Laplacian matrix on training data. Normally, a given multimedia sample is usually associated with multiple labels, which are inherently correlated to each other. Although traditional methods could solve this problem by translating it into several single-label problems, they ignore the correlation among different labels. In this paper, we propose a novel semi-supervised feature selection method and apply it to the multimedia annotation. Both labeled and unlabeled samples are sufficiently utilized without the need of graph construction, and the shared information between multiple labels is simultaneously uncovered. We apply the proposed algorithm to both web page and image annotation. Experimental results demonstrate the effectiveness of our method.     

利用PowerPoint软件制作多媒体教学课件

阐述了多媒体教学课件所应具有的主要特征,然后介绍了利用PowerPoint制作课件的优点及采用该软件制作多媒体教学课件的一般步骤及技巧.     

海事卫星系统发展及应用

介绍了海事卫星系统的发展概况,包括海事卫星主要技术参数和各种终端,如B/M终端、FLEET终端、BGAN终端等。详细论述了BGAN系统及其终端,包括构成、主要性能和关键技术。从技术、业务和设备实现等角度概括了系统发展特点。给出了海事卫星系统主要应用领域,包括远洋运输、航空通信、陆地移动、应急通信及记者新闻采访。     

链路聚合在海事卫星网络中的应用研究

通过海事卫星传输流媒体视频已成为当前通信领域发展的热点,但海事卫星由于其本身通信资源的不足,其提供的带宽尚很难满足高码率的实时视频传输需求。针对这一问题,提出了一种链路聚合解决方案,通过链路聚合多路卫星链路,采用对流媒体视频数据进行分拆、传输路由分配和控制、以及数据缓冲、帧失序控制等方法,实现数据传输速率的提高,从而有效提升海事卫星链路流媒体视频的传输质量。     

基于协议转换的卫星通信系统的应用

探讨解决互联网到国际移动卫星C系统的通信协议转换问题。采用的方法是通过互联网的Telnet协议来仿真PSDN网络的X.25协议,通过2种协议的转换来实现互联网和卫星C系统的信息交互,并保持了原有用户直接使用X.25连接的访问习惯和指令集。采用X.25协议的单进程模式并结合虚拟多条电路方式对应互联网的多个Socket链接,该方法使得系统支持并发用户访问,并且提高访问速度和通信的稳定性。     

海事卫星BGAN信号盲解调技术研究

研究了海事卫星BGAN系统中QPSK调制信号的盲解调技术.在没有信号先验知识的情况下,首先对QPSK信号进行了载波和码速率的精确估计,然后利用V&V算法进行初相位估计,去除载波信息;最后利用位同步估计算法,进行最佳抽取和比特判决,并针对V&V算法存在的4种相位模糊,利用BGAN的UW字段来解决模糊问题.经过比特文件的分析,证明此方法在几乎全盲的条件下盲解调有效.     

A Cross-Layer Packet Scheduling Scheme for Multimedia Broadcasting via Satellite Digital Multimedia Broadcasting System [Advances in Mobile Multimedia]

In recent years, multimedia content broadcasting via satellite has attracted increased attention. The satellite digital multimedia broadcasting (S-DMB) system has emerged as one of the most promising alternatives for the efficient delivery of multimedia broadcast multicast service (MBMS). The design of an efficient radio resource management (RRM) strategy, especially the packet scheduling scheme, becomes a key technique for provisioning multimedia services at required quality of service (QoS) in S-DMB. In this article, we propose a novel cross-layer packet scheduling scheme that consists of a combined delay and rate differentiation (CDRD) service prioritization algorithm and a dynamic rate matching (DRM)-based resource allocation algorithm. The proposed scheme considers multiple key factors that span from the application layer to the physical layer, aiming at simultaneously guaranteeing diverse QoS while utilizing radio resources efficiently under the system power and resource constraints. Simulation results demonstrate that the proposed cross-layer scheme achieves significantly better performance than existing schemes in queuing delay, jitter, and channel utilization.     

第四代海事卫星系统技术特点

经过多年来的发展和技术的不断提升,海事卫星已发展成为世界上惟一能为海、陆、空领域用户提供全球覆盖、全天候工作、全业务支持的移动卫星通信系统。本文主要介绍第四代国际海事卫星的技术特点和业务发展。     

Inmarsat系统及其在突发事件中的应用

Inmarsat系统在全球各类突发应急事件中是一种重要的应急通信保障手段,本文介绍了此系统的现状及其最新代系统下的BGAN．FleetBroadband．SwiftBroadband业务,最后介绍了该系统在各种突发应急事件中的主要应用。     

海事卫星信号接收处理系统实现方案

针对日益增强的反恐和安全防护需求,分析了海事卫星信号接收处理的可行性,提出了海事卫星信号接收处理系统的实现方案。该方案在侦测一体化的基础上,通过运用上行信号引导的工作方式,解决了对一定范围内的目标进行抵近接收的问题。与以往的方案相比,所提方案从系统角度研究解决了海事卫星信号接收、解调等关键问题。试验表明,本系统方案能够对实际海事卫星终端的上下行卫星信号进行实时接收处理,具有很好的工程应用价值。     

基于Inmarsat的无线数字通信的研究与实现

本文就通过Inmarsat系统进行无线数字通信的可行性和实现进行了研究,主要介绍无线通信协议、压缩、纠错方式,数据包大小选择,以及通信过程实现等关键技术。     

基于HLA的Inmarsat卫星仿真系统设计研究

通过对Inmarsat卫星系统中各类工作单元进行分析,结合应用高层体系结构(HLA),建立了一种Inmarsat卫星通信的分布式仿真系统,对系统各部分之间的逻辑关系、交互和运行过程进行了分析研究,在此基础上重点进行了系统联邦成员、对象类/交互类的研究和设计,给出了仿真开发过程,实现了仿真软件系统的基本构架。     

海事卫星通信系统VoIP技术的应用分析

随着VoIP技术的发展,VoIP技术结合卫星通信网络的应用越来越广泛。Inmarsat卫星系统是地球同步轨道系统,网络传播时延大,卫星VoIP电话的语音通信是否可行值得研究。结合VoIP关键技术和海事卫星通信语音通信应用场景,探讨了基于Inmarsat卫星网络实现VoIP技术的方案,并分析出此方案下VoIP系统通话过程的单向时延为350 ms,低于ITU G.114的400 ms的要求。在实际使用环境中进行了测试和验证,结果表明,基于Inmarsat网络下实现VoIP的方案是可行的。该方案实现复杂度低,可以方便地实现Inmarsat网络与地面电话网之间的互联互通,也可以为我国自主研制的宽带卫星通信系统实现VoIP技术提供参考。     

第四代海事卫星陆用型终端应用中的技术问题与解决措施

本文从目前用户在第四代海事卫星陆用型终端应用中涉及的问题入手．对海事卫星网络结构特点进行了分析．进而提出了具体的解决措施,对用户更好地使用海事卫星业务具有现实的指导意义。     

国际海事卫星系统在灾害性天气报道中的应用

国际海事卫星系统在气象灾害性天气直播报道和素材回传发挥了重要的作用.本文首先介绍现有海事卫星系统结构、功能、技术特点,以及针对灾害性天气报道的技术贴合性和环境适应性.通过中国气象频道海事卫星直播方案,阐述了海事卫星技术在灾害性天气直播报道的应用效益.最后展望了下一代海事卫星的发展情况在气象新闻报道中的应用前景.     

电离层闪烁对海事卫通HSD传输性能的影响

海事卫星通信B系统是重要的岸船通信系统,基于该系统的高速数据传输业务是重要的岸船综合数据传输方式。针对该系统高速数据传输(HSD)在远洋海区通信任务中出现的信号强度不稳定、突发误码增多、系统误码率偏高等问题进行了原因分析。提出了电离层闪烁对海事卫星HSD传输性能存在一定影响的意见。通过对电离层振幅闪烁信号进行建模仿真,验证了电离层闪烁导致海事卫通HSD传输性能下降、突发误码增多的结论。