卫星会议电视系统及网控技术

介绍了一种卫星会议电视系统,它利用IBS／IDR技术进行业务信息传输,利用TDM／TDMA技术进行网控信息传输。重点介绍了卫星会议电视系统中的关键技术之一－－网控技术,包括会议网管系统、卫星会议电视多点控制器和远端控制器、网控信道TDM／TDMA调制解调器、TDM／TDMA帧结构等,并对网控信道性能进行了分析。     

卫星电视地面接收系统的调试与维护

卫星电视节目是有线电视前端系统的主要信号源 ,卫星系统的调试和维护是保证有线电视信号质量很重要的一环。1　卫星电视接收系统卫星电视地面接收系统主要有 :接收天线 (包括馈源 )、低噪声下变频器 (高频头ＬＮＢ)和卫星接收机 (或卫星综合解码接收机ＩＲＤ)。1.1　接收天线卫星接收天线的种类很多 ,有不同口径的天线 ,有前馈型和后馈型天线 ,有板状和网状天线 ,有Ｋｕ波段和Ｃ波段天线 ,有电动极轴天线和多馈源多波束天线等。在选购天线时有以下几点可以借鉴 :一是在前馈天线和后馈天线的选择上 ,一般来说收发合用的卫星通信站宜选后馈天…     

基于LXI技术的网络化卫星测试系统设计

LXI总线技术应用于卫星测试系统,可以很好地解决分布式测试、远程测试和异构测试系统融合等问题.首先介绍了LXI总线技术的特点以及相对其他总线的优势,然后提出新一代基于LXI总线技术的卫星测试系统体系结构,从通用、互换、兼容等方面考虑进行了整个卫星测试系统的方案设计.     

Margin measurements in optical amplifier system

The margin, or the difference between the received signal-to-noise (SNR) and the SNR required to maintain a given bit error ratio (BER), is important to the design and operation of optical amplifier transmission systems A new tehnique is described for estimating the SNR at the receiver's decision circuit when the BER is too low to be measured in a reasonable time. The SNR is determined from the behavior of the BER as a function of the decision threshold setting in the region where the BER is measurable. The authors obtain good agreement between the BER predicted using the measured SNR value and the actual measured BER     

Ka-band propagation measurements: an opportunity with the AdvancedCommunications Technology Satellite (ACTS)

The Advanced Communications Technology Satellite (ACTS) was conceived at the National Aeronautics and Space Administration (NASA) as a follow on program to its long history in satellite communications projects that have reduced the risk of developing new technologies that fall outside the sponsorship capability of the private sector. To counter the foreign challenge that developed in the late 1970's to the once insuperable US lead in this field, ACTS was developed to maintain the US preeminence. Launched in September 1993 from the space shuttle, key technologies on ACTS include a multibeam antenna, a baseband processor, a 900 MHz wideband microwave switch matrix, adaptive rain fade compensation techniques, and the use of Ka-band frequencies. Since this is the United States' first effort in using Ka-band for satellite communications, beacons are incorporated on the satellite, which provide an opportunity for propagation measurements. NASA is sponsoring a network of propagation experimenters using these beacons and receive-only terminals identical in design. This paper provides some history that leads to the eventual development of ACTS. Also, a system overview of the spacecraft is provided for those less familiar with it     

Satellite communications relay system using a retrodirective space antenna

A system has been developed for relaying messages via a satellite between earth points. In this system, messages transmitted to a satellite modulate a retrodirective antenna. Earth stations receive messages by irradiating the satellite antenna. Methods of modulating the retrodirective array are discussed with emphasis on methods to facilitate communications among several ground stations. There are advantages in spectrum usage and sharing with surface facilities. System design parameters are presented. Minimal power is required in the satellite as compared to the active communications satellites. Extremely high reliability is inherent in the design of the satellite electronic system, which can be made entirely from solid-state components.     

GPS synchronized power system phase angle measurements

Before a major new 500 kV transmission line was placed in service between Oregon and the San Francisco, California area, a series of high-voltage short circuit tests were performed on the transmission system. The short circuit faults produced a brief ‘delta function’ shock to the regional power system. This paper discusses the use of Global Positioning System (GPS) synchronized equipment for the measurement and analysis of key power system quantities. Before the testing, the authors installed two GPS synchronized phasor measurement units (PMUs). The PMUs use GPS to globally synchronize the measurement of the state vector of the power system, the complex voltages of substation busses. Complex voltage means the magnitude and the relative phase angles of substation voltages. GPS provides the global time reference marker for phase angle measurement. One electrical degree of the 60 Hz waveform equals about 46 μs. Across short transmission lines (less than 50 km), measurements may need to be made to 0.1 electrical degree, which translates to clock synchronizations of roughly 5 μs. The PMUs recorded the dynamic response of the power system phase angles when the northern California power grid was excited by the artificial short circuits. Power system planning engineers perform detailed computer generated simulations of the dynamic response of the power system to naturally occurring short circuits, e.g. faults caused by lightning. The computer simulations use models of transmission lines, transformers, circuit breakers, and other high voltage components. This work will compare computer simulations of the same event with field measurements.     

Integrated-optic system for high-speed photodetector bandwidth measurements

A novel measurement system based on an integrated-optic modulator has been used to determine the frequency response of a high-speed GaInAs photodiode. A nominally 8 GHz bandwidth modulator provided a 3 mu W levelled, continuously tunable, modulated optical signal to greater than 21 GHz. The measured detector 3 dB bandwidth was 19.2+or-0.8 GHz.<>     

Satellite repeater arrangement in a new maritime mobile telephone system

A new maritime mobile radio telephone system adopted by Nippon Telegraph and Telephone Public Corporation (NTT), is described. An outline of the technical features of the entire system and the satellite repeater arrangement, adopted to reduce service-dead areas, is given.     

基于IDBS的卫星数据广播系统及应用

介绍了IDBS的系统结构和协议层次，描述了采用多播数据缓存技术的IDBS系统结构，IDBS为高速英特网接入，多媒体技术应用提供了一种廉价、高效的途径。     

卫星互联网下的VSAT卫星通信

本文介绍了VSAT通信在卫星互联网下的新发展,分析了VSAT系统的互联网接入方式,研究了卫星互联网的技术热点,展望了卫星互联网的发展前景.     

基于北斗卫星导航的车辆监控系统

针对我国现阶段普遍使用的基于GPS的车辆监控系统,设计了一套基于我国自主研发的北斗卫星导航系统的车辆监控系统。与传统的GPS车辆监控系统相比,其在安全性、保密性、自主度等方面更加卓越。实践表明：我国自主研发的北斗卫星导航系统在PC-Android这一套体系中可以充分体现其优越性,同时系统特别设计了历史路径查询和借出车辆跟踪功能,在内部车辆统一管理与监控方面取得了显著的成果。     

Multivariate statistical integration of Satellite infrared and microwave radiometric measurements for rainfall retrieval at the geostationary scale

The objective of this paper is to investigate how the complementarity between low earth orbit (LEO) microwave (MW) and geostationary earth orbit (GEO) infrared (IR) radiometric measurements can be exploited for satellite rainfall detection and estimation. Rainfall retrieval is pursued at the space-time scale of typical geostationary observations, that is at a spatial resolution of few kilometers and a repetition period of few tens of minutes. The basic idea behind the investigated statistical integration methods follows an established approach consisting in using the satellite MW-based rain-rate estimates, assumed to be accurate enough, to calibrate spaceborne IR measurements on sufficiently limited subregions and time windows. The proposed methodologies are focused on new statistical approaches, namely the multivariate probability matching (MPM) and variance-constrained multiple regression (VMR). The MPM and VMR methods are rigorously formulated and systematically analyzed in terms of relative detection and estimation accuracy and computing efficiency. In order to demonstrate the potentiality of the proposed MW-IR combined rainfall algorithm (MICRA), three case studies are discussed, two on a global scale on November 1999 and 2000 and one over the Mediterranean area. A comprehensive set of statistical parameters for detection and estimation assessment is introduced to evaluate the error budget. For a comparative evaluation, the analysis of these case studies has been extended to similar techniques available in literature.     

Reproducible modal noise measurements in system design and analysis

The need to predict modal-noise performance limitations in optical-fiber systems has led to noise characterization techniques based on probability density functions. These have been used for evaluation of both components and systems, and are found to give meaningful and repeatable data. The modal-noise probability density function (PDF) can be generated from several individual readings which provide information on the probability of any noise level by extrapolation.     

RCS measurements and results of an engine-inlet system designoptimization

A number of papers have been published on the prediction of backscatter from engine-inlet-type structures. Measured data used to verify these predictions mostly consists of backscattered data from canonical structures, e.g., cylindrical waveguide cavities. In this paper, measured backscattered data for an unmanned aerial vehicle-type engine-inlet system is presented. The effects of the application of radar-absorbing materials to the engine-inlet system on the contribution to the RCS is discussed, and data measured in a compact-range facility are presented     

Distributed measurements for estimating and updating cellular system performance

We investigate the use of distributed measurements for estimating and updating the performance of a cellular system. Specifically, we discuss the number and placement of sensors in a given cell for estimating its signal coverage. Here, an outage is said to occur at a location if a mobile receiver there has inadequate signal-to-noise ratio (SNR -based outage) or, using another criterion, inadequate signal-to-interference ratio (SIR- based outage); and the outage probability is the fraction of the cell area over which outage occurs. A design goal is to improve measurement efficiency (i.e., minimizing the required number of measurement sensors) while accurately estimating the outage probability and mapping the coverage holes. The investigation uses a generic path loss model incorporating distance effects and spatially correlated shadow fading. Our emphasis is on the performance prediction accuracy of the sensor network, rather than on cellular system analysis per se. Through analysis and simulation, we assess several approaches to estimating the outage probability. Applying the principle of importance sampling to the sensor placement, we show that a cell outage probability of P_o can be accurately estimated using ~ 10/P_o power-measuring sensors distributed in a random uniform way over the area with base-sensor distances from 50% to 100% of the cell radius. This result applies to both SNR-based and SIR-based outage estimation for both indoor and outdoor environments.     

Satellite Beam Optimization for the Broadcasting Satellite Service

In view of the forthcoming ITU Regional Administrative Radio Conference for the planning of the Broadcasting Satellite Service at 12 GHz for the American Continent to be held in 1983, there is a need for a means to transfer the service quality requirements for a Broadcasting Satellite Service into a consistent set of satellite and receiving terminal parameters.     

新型数字卫星接收机的寻星功能

分析近几年来推出的新型数字卫星接收机的寻星功能包括寻星指示和接收参数扫描两大功能,以及这些功能特点在寻星操作中的运用。