Inmarsat BGAN系统（上）

本文从空间段，地面段和用户段三方面详细介绍了Inmarsat BGAN系统的组成及其功能；分析了BGAN系统的主要技术指标并总结了它的主要关键技术，指出了Inmarsat 4空间段的先进性和优越性能，最后指出了它能够提供的各种业务类型和主要应用场合。     

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。     

Voice transmission quality of mobile satellite communications systems

Recently, a number of commercial digital mobile satellite communications systems have become operational, and the introduction of more systems is imminent. The voice transmission quality of the Inmarsat-aeronautical, Inmarsat-M and Inmarsat-B systems was evaluated and compared with the quality of the Inmarsat-A analogue communication system on the basis of subjective listener opinion assessments. From this evaluation it can be concluded that, under nominal operating conditions, the current generation of digital mobile systems may offer a perceived performance that surpasses that of the older Inmarsat-A analogue system, at least when measured in terms of transmission quality.     

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。     

基于InmarsatD+的船舶遥测监控通信系统的实现与研究

InmarsatD+是Inmarsat近年推出的一种新颖的用户服务,它在遥测监控通信系统中的应用在国内外都是一种新的技术。通过与现有遥测监控通信系统的比较,阐述了基于InmarsatD+的遥测监控通信系统的优越性及其组成,并以一个基于InmarsatD+的船舶遥测监控通信系统为例,剖析了这种新颖的监控中心系统的体系结构。该系统在国内某船舶管理机构试运行效果良好。     

Inmarsat移动卫星通信系统中Turbo码的应用

在分析Turbo码结构和原理的基础上，介绍了Inmarsat-M4和Inmmarsat-F系统中实现“压缩频带的高速数据(HsD)传输”的核心技术。着重阐述Turbo码多电平调制结合方式、信道状态信息提取、译码算法和实现上有待解决的关键问题。     

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。     

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。     

海事卫星通信的发展应用现状初析

本文分析了各类海事应用对卫星通信的需求．研究了各类海事卫星通信系统的当前应用现状,介绍了各主要海事卫星服务供应商新推出的各项服务．最后．对海事卫星应用前景进行了展望。     

Land vehicular propagation channel characterization of BGAN system

This paper summarizes the results of a measurement campaign, which set out to characterize Inmarsat's broadband global area network extension (BGAN‐X) L‐band land vehicular (LV) channels as a function of elevation angle and candidate antenna systems. Measurements were conducted with three types of directional antennas on motorway routes around London using Inmarsat's Indian Ocean Region (IOR), Atlantic Ocean Region‐East (AOR‐E) and Atlantic Ocean Region‐West (AOR‐W) satellite transmissions, corresponding to elevation angles of, respectively, ～7.5°, ～13° and ～30°. Simultaneous recordings of data on two types of directive receivers enabled correlation of several channel parameters. Statistics were used to refine a baseline model that derived BGAN‐X LV channel parameters by scaling the statistics obtained from an omni‐directional antenna receiver. The measurements demonstrate that Ricean mean and Ricean factor vary significantly over the chosen routes at elevation angles below ～13°. Further, the Doppler shift of the direct path can be predicted accurately. A qualitative analysis indicates that the multi‐path Doppler spread is generally (not always) caused by uniform scattering around the vehicle over short distances and undergoes spatial filtering due to the receiver antenna. A technique was established to derive statistics of a two‐state Markovian channel model at any specified fading threshold by gathering tracking system state, thereby allowing one to ascertain service expectations and operational parameters such as connection time‐out of a packet‐switched system or reliability threshold of a circuit‐switched system. The technique was used to identify and select appropriate routes, particularly for the IOR and the AOR‐W regions. Data analysis is in progress to establish the reason for the slow variations of signal mean at low‐elevation angles in Ricean conditions and to derive appropriate statistical models. Furthermore, image processing of the video recordings is expected to reveal the extent of optical and RF fades correlation. Copyright © 2008 John Wiley & Sons, Ltd.