卫星通信行业的技术应变与商机(续)

四、Ku资源的充分发掘和使用 卫星通信在带宽上的客观限制是无法改变的。常用于静止通信卫星的C频段和Ku频段已被捷足先登者瓜分殆净。尚未充分开发使用的Ka及更高频段，由于很难抵抗降雨衰耗的影响，通常被认为不适用于VXAT，而只适于大天线的宽带应用。 大口径地面天线对邻星的偏轴干扰相对较小，抑制邻星干扰的能力也较强。从理论上说，只要相邻卫星的地面系统都加大天线口径，就可以减小通信卫星的轨位间隔。国际电联在邻星协调方面的规则支持先登先占。在轨卫星的操作者出于保护己方商业利益的考虑，轻易不会同意减小现行地面系统…     

卫星通信在水利行业的应用与发展

本文主要综述了卫星通信的发展历史、现状和未来的发展趋势,分析了卫星宽带技术和激光卫星技术的发展,结合水利行业的需求,阐述了卫星通信在水利行业中的应用和发展。     

卫星通信技术与应用发展

一、卫星通信简史 1945年5月英国科幻作家克拉克(Arthur C.Clarke)在《无线电世界》(Wireless World)建议,利用位于与地球转速一样的轨道上的人造空间站系统进行全球通信。这可算是提出地球同步卫星通信概念的第一人。他的那一段文字是这样写的:“一颗距地球恰当距离的‘人造卫星’将每24小时转一圈,也就是说,它将在地球某点上空固定不动,而且其可视范围几近半个地球表面。3个在适当轨道上相距120度的转发     

卫星通信技术新进展——个人卫星通信

从世界上成功的发射第一颗卫星至今，已经历了30多年的历程，卫星通信从民用发展到军用；从模似发展到数字；从固定发展到移动通信；进而向个人通信发展．目前，它广泛地用于国际通信，区域通信，及边远地区通信，并对社会经济，文化、政治，军事、外交等领域发挥了巨大作用．     

试论中国卫星通信行业的发展创新

在通信卫星、轨位和频谱资源、地球站设备和卫星通信网等方面,对中国卫星通信行业的技术创新和行业发展,提出了一些策略性设想和具体化建议.     

卫星通信技术的新进展

本文对国内外卫星通信的最新发展作了详尽论述；并综合概括了未来卫星通信技术的发展趋势；最后，对卫星通信市场进行了预测。     

卫星通信技术的新趋势

卫星属于高速以及高空运转的一种科学性的仪器,属于是综合了遥感以及测量等多种科学的一个综合体。卫星在实际的地球运行轨道当中,能够以其自身比较独特的角度实施相关的工作,卫星的一个非常必然的发展趋势是卫星通信,同时还能够有效保证卫星的实际运行。在文章中,简单分析了卫星通信技术以及卫星通信网络,并详细描述了其中所运用的主要技术,最后给出了卫星通信技术的未来发展趋势。     

Mobile satellite communications

The paper presents an up-to-date overview as well as new results on mobile satellite communications. Specifically, the following subjects are addressed: worldwide activities; satellite orbits; multiple access techniques; Novstar global positioning system; economic and regulatory issues; future trends. Some of these technical and nontechnical subjects appeal disjoint, but they are unique and significant among the many facets, which effect the development and operation of mobile satellite communication systems     

Microscale diversity in satellite communications

Results from an investigation into a microscale diversity scheme for the purpose of mitigating attenuation due to tropospheric scintillations are presented. Data from an experiment using the 20-GHz Olympus satellite beacon were analyzed to evaluate the performance of short-baseline site-diversity systems. Results indicate that with a baseline separation of about 50 m (at an elevation angle of 14° in this experiment) the signals received by the main and diversity terminals become decorrelated. Examination of several high-scintillation events shows that such a diversity technique could substantially increase the uptime of low-power-margin VSAT systems. The performance of microscale diversity for several baseline separations is evaluated in terms of a parameter called diversity recovery. Applications and conditions under which microscale diversity performs best are addressed     

Modem techniques in satellite communications

Since the mid 1980s, research and development in satellite modem techniques has been very active and has yielded promising results. In the article the author presents a summary of the current status of work in this area, and discusses the directions this work is taking     

差错控制编码在卫星通信中的应用

本文回顾了差错控制编码在航天卫星通信中30多年来的发展概况,重点介绍和分析了CCSDS级联码标准及其改进译码方法。文中还对近来出现的Turbo码的原理与特性进行总结,分析了Turbo码在卫星通信中应用的主要问题     

Personal communications by satellite

Personal communications (PC) refers to two-way voice (and possibly data) communications to a small hand-held unit, capable of being carried by a person and used in various locations. PC via satellite refers to the case where this hand-held unit communicates directly with a satellite to provide the duplex voice (or data) service. Both geosynchronous earth orbit (GEO) and low earth orbit (LEO) satellites have been considered to provide this service. GEO and LEO satellite systems must compete with existing mobile cellular radio systems both in meeting performance requirements and service costs, if they are to be a significant supplier of PC services. GEO and LEO systems each have unique advantages and disadvantages when used to provide a PC service. While these general characteristics are identified in Section 1 of the paper, a more quantitative comparison is needed. This quantitative comparison is made by comparing a GEO PC satellite system, operating at EHF (K_a-band) frequencies with a LEO system operating at UHF (L-band) frequencies, including service costs for both systems. The two systems used in the comparison are examples of realistic GEO and LEO system designs for PC service, and although it is not exhaustive, the comparison points out some of the key differences between GEO and LEO systems that affect service performance and cost.     

Commercial satellite communications experience

The operational Intelsat I (Early Bird) and Intelsat II satellites and associated earth stations that comprise the present commercial satellite communications system provide a capacity of close to 720 voice circuits between major earth stations. All but a limited portion of the inhabited globe is now within the line of sight of a commercial satellite relay. In addition, it is expected that by 1968, with the operation of Intelsat III, a truly global international satellite communications system will exist.     

GaAs FET satellite communications

What is claimed to be the industry’s first 90W c-band GaAs field effect transistor (GaAs FET) suitable for use in solid-state power amplifiers (SSPA) for base station or earth-station satcom and radar applications, as well as for microwave digital radios for terrestrial communications, has been released by Toshiba America Electronic Components Inc. Using TAEC’s HFET process technology, the TIM5964-90SL GaAs FET employs ion plantation technology to produce an output power of 49.5dBm at a frequency range of 5.9GHz to 6.4GHz. and is priced at around $1,500 each.This is a short news story only. Visit www.three-fives.com for the latest advanced semiconductor industry news.     

Blockage mitigation techniques in satellite communications

This article proposes systematic approaches to minimize severe channel degradation. Detection of channel condition is performed by means of two continuous ARQ NAK counting schemes. Stop-and-wait ARQ non-NAK counting is used for timed complete blockage. A single (31,21,5) code is designed for all the ARQ systems proposed. After the blockage state of a transmission channel is determined, satellite link parameter trade-offs and other specific remedy alternatives are recommended to enhance channel performance. System performance criteria are derived with different Earth station capabilities.