外军新一代移动卫星通信天线及其装备简介

美国通用动力卫星通信技术公司业务开发部副总裁马文·休梅克认为，当今天线技术开发领域中，最活跃的便是可用于陆地、海洋和机载应用的移动卫星通信天线技术。目前，美国的移动卫星通信系统正在从驻停式设计向全速移动设计转型，随之产生了新一代天线及装备配置。     

一种高性价比船载卫星通信天线系统的设计与应用

根据目前移动卫星通信站应用的实际情况,结合市场上主要相关移动卫星通信站产品的设计原理及技术原理,探讨船载"动中通"卫星通信天线的设计原理及相关技术应用,给出多种设计方案,并进行系统性比较,旨在寻找一种最优性价比的船载"动中通"卫星通信天线系统的设计方法,提供低成本"动中通"卫星通信天线系统的构建思路,使移动卫星站的建设和应用范围更广阔,更适合于民用及低成本应用领域,解决广阔海域范围内的多媒体通信问题,有效延伸飞速发展的信息高速公路。     

WCDMA体制卫星通信系统抗衰落技术研究

卫星通信是重要的现代通信技术之一,宽带码分多址(Wideband Code Division Multiple Access,WCDMA)卫星通信系统是当前卫星通信界的研究热点。通过比较和分析陆地移动信道和地球静止轨道(GEO)卫星信道的差异,研究了WCDMA的抗干扰技术在GEO卫星通信中的适应性问题。针对GEO卫星信道慢衰落、长相干时间和长时延的特点,在功率控制、交织方式和帧结构设计3个方面提出了改进方案。     

高轨道（同步轨道）移动卫星通信系统

本文较详细分析了几种高轨道（同步轨道）移动卫星通信系统（ＩＮＭＡＲＳＡＴ、ＭＳＡＴ和ＡＰＭＴ）的系统设计，并对设计高轨道移动卫星通信系统要解决的几个关键技术问题进行了讨论，最后对我国如何发展移动卫星通信系统提出几点技术建议。     

用于移动卫星通信系统的DCA技术

本文首先概要阐述卫星通信、移动卫星通信在建立国家信息基础结构(NII)即信息高速公路中的地位,然后着重分析应用在移动卫星通信系统中的DCA技术.DCA技术具有通话丢失率低,抗干扰性能好等特性.     

Ka频段卫星通信地空链路的大气衰减

在卫星通信系统的设计中,设计人员往往更关心降雨对电波传播造成的降雨衰减,而易忽略在一般情况下晴空大气对卫星通信地空链路微波传播的影响。但是当系统的链路余度较小、天线仰角较低的情况下,应考虑晴空大气造成的衰减。论述了 Ka 频段卫星通信链路大气衰减的计算方法,给出了计算结果,可供从事类似工作的相关人员参考。     

ViaSat欲收购JAST天线系统

近日,ViaSat公司表示已达成收购JAST天线系统的意向,此项收购将拓展ViaSat在移动卫星天线产品和技术方面的业务领域。JAST致力于拓展微波电路和天线系统在地面和卫星通信中的多种应用,特别是应用于移动卫星通信的小型天     

计算机仿真在混合星座通信性能研究中的应用

目前卫星通信系统中的混合星座设计是一个热点研究问题.本文分析了GEO和IGSO组成的混合星座的星座覆盖性能、对地通信时长等问题.研究表明,采用2颗或3颗IGSO卫星构成的星座能够提供较好的覆盖性能(多星覆盖率及高通信仰角),采用混合星座能够有效解决GEO卫星在高纬度区域的低仰角问题,满足某些特殊区域的应用需求.因此,采用GEO和IGSO的混合星座通信系统具有较好的技术可行性.     

ViaSat力推新一代移动卫星通信系统——ArcLight产品专题研讨会在京举 办

作为全球著名卫星通信行业的制造商,美国卫讯公司（ViaSat,Inc）致力于研发和生产创新的卫星通信和与其相关的无线网络技术产品．其专利技术的ArcLight产品采用了目前最先进的扩频通信技术,现正在为全球航空、海运船舶和地面交通等领域的用户提供真正意义上的宽带移动卫星宽带通信服务。为了让更多的中国用户进一步了解ArcLight产品,ViaSat公司于2009年1月13日在北京举行了新一代宽带移动卫星通信系统——ArcLight产品专题研讨会。会议由ViaSat公司大中国区总裁韩经准博士主持,     

全球星低轨移动卫星系统及其应用

低轨移动卫星通信的发展给实现通信的全球化和个人化带来了更多的机会和选择。不同系统的不同设计思路带来了系统之间的差异,同时也决定了其在通信市场中的位置。本文介绍全球星低轨移动卫星通信系统的设计思想、技术体系和终端设备以及目前的实施情况。     

A Trace-Time Framework for Prediction of Elevation Angle Over Land Mobile LEO Satellites Networks

Elevation angle is one of the most significant parameters of land mobile satellite channels, subject to rapid variations in the case of Low Earth Orbit (LEO) satellite systems. In this paper a novel trace-based framework is proposed and analyzed which is capable of predicting elevation angle as a function of time during satellite visibility window. Trace-time based modeling makes the framework practical for real-time evaluation of elevation angle and its alteration incurred by communication links in LEO satellite systems. The proposed method is particularly suitable for development of communication channel models and services in mobile LEO satellite networks where path variability is of great importance.     

Satellite diversity in mobile satellite CDMA systems

The paper addresses the exploitation of satellite diversity in a satellite mobile network. In particular, we focus on the impact of diversity on service availability and on system capacity, considering the forward link of a CDMA system with a multisatellite and multibeam architecture. The analysis includes the effects of path blockage, intrabeam and interbeam interference, imperfect power control, and fading correlation in the time-domain due to nonideal interleaving. A closed-form solution is given for the estimation of system capacity. We show that satellite diversity is essential in providing service availability in urban and suburban areas, while the impact of satellite diversity on system capacity may be positive or negative, mainly depending on the fading channel characteristics. In particular, diversity becomes more and more beneficial for increasing fading time-domain correlation (i.e., for low mobile speed and/or limited interleaving depth). The analytical results have been validated by means of Monte Carlo simulation     

Analysis of coded noncoherent transmission in DS-CDMA mobilesatellite communications

The paper analyzes possible transmission schemes for satellite personal communication systems adopting low/medium-Earth orbit (LEO/MEO) constellations and direct-sequence code division multiple access (DS-CDMA) in the presence of fading and shadowing, the statistics of which are functions of the satellite elevation angle. In particular, the performance of M-ary Walsh-Hadamard orthogonal (MWHO) convolutionally coded DS-CDMA over a Rice-log-normal fading channel is analyzed in depth, and compared to the simpler coded differential BPSK (DBPSK) scheme. Optimization of the performance/complexity tradeoff in the metric computation for soft inputs to the Viterbi (1979) decoder is addressed. Upper bounds on the error probability without or with satellite diversity and equal gain combining are evaluated considering different coding rates. The effect of correlated fading is also taken into account via simulation. Among the various results, it is shown that the optimal coding rate is a function of the satellite elevation angle and of the diversity order, that the loss for using DBPSK instead of MWHO is in the range 1-1.4 dB, and that interleaving depth is a critical parameter     

Forward Error Correction Coding for Fading Compensation in Mobile Satellite Channels

Fading in mobile satellite communications severely degrades the performance of data transmission. The channel is modeled with nonfrequency selective Rice and Rayleigh fading. Also, stored channel simulation is used for hardware data transmission. FEC coding with Viterbi decoding of convolutional codes, and Berlekamp-Massey decoding of Reed-Solomon codes, are used to compensate for the fading. In addition to interleaving, channel state and erasure information improve the performance of the decoder. The BER after decoding is calculated for specific codes on several channels and for different transmission schemes. Using very simple channel state and erasure information gives 2-7 dB additional coding gain. These gains have been verified by hardware data transmission on synthetic fading channels and stored mobile satellite channels.     

Reed-Solomon codes for land mobile satellite channels

The performance of Reed-Solomon codes is determined for land mobile satellite communications where a shadowed Rician channel model is used. An effective coding/interleaving scheme is proposed which uses the multipath fading and shadowing statistics of the channel.<>     

Burst-Error Correction Strategies in a Slotted DS-CDMA Mobile Satellite Channel

Various burst-error handling strategies exist to reduce the effects of bursts of errors such as those that characterise a heavily shadowed, slowly fading land mobile satellite channel using low earth orbit satellites (LEOS). It is proposed that a combination of the techniques with code rate adjustment and channel-state sensing leads to high performance gains for the direct sequence CDMA channel.This paper presents studies of the performance of code interleaving in co-ordination with code rate reduction in a channel with known burst statistics where provision is made for channel-state sensing. The results are compared with those from concatenated coding and hybrid automatic repeat request (hybrid ARQ) with selective repeat (SR).Results are presented for throughput and delay. The combination of the various techniques for specific channel conditions results in significant performance improvements in terms of throughput and average time delay. The proposed error-control technique offers significant performance gains over the use of hybrid ARQ, concatenated coding or interleaving in isolation.     

卫星移动通信中的抗多径衰落技术

在移动卫星系统中，多径衰落是影响通信质量的重要因素之一。本文对目前在移动卫星中应用比较广泛的抗多径衰落技术进行了归纳与总结，并分析了四种的典型的抗衰落技术，最后给出了选择抗多径衰落技术方案的一般性原则。     

MoM solutions to building blockage of mobile satellite communications

This article presents a full-wave propagation model for arbitrary profile of building blockage in mobile satellite communications, by solving the electric field integral equation for induced surface currents using the method of moments. Asymptotic expressions are used to simplify the integrals. Scattered fields are then found by the radiation equations derived from Maxwell equations. The total received fields around different profiles of buildings are calculated as a function of space, elevation angle and frequency. The results agree well with measurements and other published data. Various useful parameters for designing robust and reliable communication systems like frequency response, average fade duration and coherence bandwidth are found. Performance of mobile satellite system is evaluated in terms of bit error rate of mobile satellite system in frequency non-selective, slowly fading channel.     

Pilot-aided coherent uplink for mobile satellite CDMA networks

A pilot-aided coherent uplink transmission scheme is proposed for mobile satellite communications at L-band. The scheme is designed to enhance link performance as compared to coded noncoherent M-ary orthogonal modulation, while maintaining small envelope fluctuations and low complexity. A rigorous analysis is performed for the proposed technique, when used in conjunction with a direct-sequence code-division multiple-access convolutionally encoded binary phase shift keying link, in a Rice-fading channel with satellite diversity. The pilot-aided scheme has been extensively simulated, accounting for finite interleaving in slow fading and nonideal carrier frequency recovery. The results show a significant performance gain with respect to noncoherent schemes designed for similar links, which goes up to 1.8 dB for 9.6 kb/s services with slow moving users exploiting dual-satellite diversity