The European system for digital multi-programme television bysatellite

The general concepts of the system for digital television transmission by satellite developed within the European DVB (digital video broadcasting) project and standardised by ETSI (European Telecommunications Standards Institute) are described. The system, named DVB-S, is intended to provide DTH (direct-to-home) multi-programme TV services in the BSS (broadcasting satellite service) and FSS (fixed satellite service) bands and is addressed to consumer IRDs (integrated receiver decoders), as well as collective antenna systems (SMATV, satellite master antenna TV) and cable television head-end stations, with a likelihood of remodulation. The exploitation of the multiplex flexibility allows the use of the transmission capacity for a variety of TV service configurations. The use of flexible and advanced error protection techniques, based on the concatenation of Reed-Solomon and convolutional codes (with Viterbi decoding), allows optimum adaptation to different satellite transponder characteristics, i.e. bandwidth and power, providing high service quality and availability with small receiving antennas. For example, in climatic zone E (in Europe) on a 33 MHz transponder a data-rate of 38.1 Mbit/s can be transmitted, adequate to provide five standard definition TV programmes (SDTV) or, alternatively three to four enhanced definition programmes (EDTV), while ensuring 99.90% service availability (in the average year) with 50-cm receiving antenna within the 51 dBW EIRP (equivalent isotropic radiated power) service area contour     

A satellite data transmission antenna

A retrodirective satellite antenna for a broad bandwidth, satellite-to-ground data transmission link, is described. An information-collecting satellite which transmits its data in the direction of the ground receiver upon command, is considered. The satellite antenna described for this system is an active retrodirective antenna which utilizes the beam-forming characteristics of a phasing matrix. A signal from the ground station is received on a particular beam port of the matrix which corresponds to a particular beam-pointing direction. Control circuitry in the satellite activates a switching matrix and a transmitter so that the data-carrying signal is transmitted in the same direction from which the satellite is interrogated. Other retrodirective techniques in addition to the phasing-matrix antenna are evaluated in terms of their relative merit. The systems considered include the active Van Atta array, the automatic three-dimensional electronic scanning, antenna (ATHESA), the Luneberg lens and various other antenna array techniques.     

Digital TV comes down to earth

The introduction of digital television, albeit with only modest pretensions to glitz, is bound to invigorate competition among manufacturers and broadcasters. The BBC and commercial TV companies in Britain will launch what looks to be the world's first terrestrial digital TV (DTTV) service intended for nationwide viewing. The British services will be the first to use ground transmitters to send digital pictures and sound to an ordinary Yagi roof antenna of the type used for analog TV in Europe or even to indoor rabbit ears. Plenty of digital receivers should be in the shops, and pay TV services, both satellite and terrestrial, will be wooing hesitant viewers with special incentives. Most other countries in Europe are also getting ready to launch DTTV services. The author discusses the phase out of analog services, digital video broadcasting standards, data rates, encryption standard, and competing digital services     

数字卫星电视接收天线仰角方位角极化角调试探讨

数字电视正以迅猛之势发展,目前数字电视信号主要是通过卫星传输,数字卫星电视信号的接收方法与模拟卫星电视信号的接收方法相同,利用室外抛物面状天线将数字卫星电视信号——电磁波接收下来,但由于数字电视信号的特点,接收数字电视卫星信号时的“寻星”过程远比接收模拟卫星电视信号困难得多,为此对数字卫星电视接收天线仰角、方位角、极化角的调试进行探讨。     

基于整网估计的星间链路天线相位中心偏差在轨特性研究

星间链路(ISL)是我国北斗三号克服区域布站、实现高精度服务的关键,其天线相位中心偏差(PCO)在设备出厂时会依据质量、设计姿态进行地面标定,但在卫星发射、入轨及在轨阶段,燃料消耗、天线展开姿态等均会引起卫星质量与姿态的变化,这将导致在轨的PCO与地面标定值不一致 ,该变化量会作为误差引入到测量值,进而影响卫星轨道确定精度。因此,该文研究了在轨卫星的星间链路天线相位中心偏差标定方法,联合星间、星地观测,建立了基于整网估计的星间链路天线相位中心偏差在轨估计方法,并利用两周的实测数据进行对北斗三号所有中轨卫星(MEO)进行验证,同时结合卫星生产商、轨道面进行在轨特性的详细分析,最后验证了其对轨道确定精度的影响。结果表明,该文方法可有效估计在轨卫星星间链路天线相位中心偏差,并发现,卫星在轨后大部分卫星的星间链路天线相位中心偏差基本与地面一致,但C36, C37, C41, C42卫星在Z方向与地面标定值存在15 cm左右的偏差,C25, C26, C43, C44在Y轴上存在符号相反的现象,且数值上有10 cm左右的偏差,C25, C26卫星在Z方向上存在近30 cm的偏差,正确标定在轨卫星星间链路天线相位中心偏差后,相比地面标定产品,轨道精度可提升15%。     

Combating sun outage in satellite television distribution systems

Two methods of sun outage avoidance in satellite television transmission are discussed. Each method requires two satellites and dual-beam antennas. The two C-band satellites transmit identical programs at the time when the sun outage period occurs. The separation of the spacecraft is dependent on the dual-feed earth station antenna size. For large television receive-only antennas, the separation must be small; for small antennas, or antennas with large beamwidths, the satellite separation can be large. If the separation is larger than 8° on the geosynchronous arc, only one transmit station is required to transmit program information. Scaling this system for Ku-band use is then considered. It is concluded that in a Ku-band direct-broadcasting system with earth station antenna diameters of 1-m and below, the rise in noise temperature due to sun outage is not significant and can be overcome by a modest amount of system margin, equivalent to that normally provided against rain fades     

卫星电视接收天线的在线调整

提出一种不中断电视信号、不携带贵重测量仪器到室外天线现场调整卫星电视接收天线的有效方法,该方法只需带1台小型电视机,具体操作有两种方案:一是将频谱仪解析出的信号频谱曲线传至天线现场进行天线调整;二是将卫星电视接收机解调出的电视画面中的菜单设置图传至天线现场进行天线调整。此方法经多年实践,行之有效,既方便又精确。     

Satellites for communications and broadcasting: The evolving european market

The paper traces the development of the market for communications and direct broadcasting satellites in Europe, since the original specification of the European Communications Satellite (ECS) in 1977. It reviews the experiments undertaken on the Orbital Test Satellite (OTS) and the way in which demonstrations with this satellite have influenced the way in which ECS is being developed. It continues by considering the impact of television on the market, first cable television and its distribution requirements, then direct broadcasting by satellite, where the introduction of homes into the customer configuration will bring with it programme content as a salient feature in market development. Finally it speculates on the possibilities for the future, both in terms of the effect of new and higher frequencies on satellite communications systems, and the possible effects that interaction from small earth-stations could have on satellite design.     

卫星接收天线的调整与卫星电视节目接收

根据实践，对卫星接收天线的调整与卫星接收机节目搜索问题进行了分析与归纳；用MATLAB编写了计算接收天线方位角、仰角和极化角的程序；给出当地方向的确定方法和地磁偏角的近似计算式，澄清了接收天线极化波容易造成的误解。     

卫星接收天线的调整与卫星电视节目接收

根据实践,对卫星接收天线的调整与卫星接收机节目搜索问题进行了分析与归纳;用MATLAB编写了计算接收天线方位角、仰角和极化角的程序;给出当地方向的确定方法和地磁偏角的近似计算式,澄清了接收天线极化波容易造成的误解。     

CAPS地面站天线跟踪卫星

地面站是卫星导航通信系统中必不可少的重要组成部分,具备接收、发射信号,监控卫星以及与地面通信网络通信交换等功能,地面站的大天线对星跟踪是卫星通信开展的基础。针对卫星地面站的重要性,介绍了CAPS(中国区域定位系统)位于北京的卫星通信地面站天线对星跟踪系统,利用该天线对准亚太I号卫星时的方位角、俯仰角以及系统AGC电平值分析了亚太I号卫星的运动轨迹,亚太I号卫星的漂移幅度在不断的增大。     

基于Kalman滤波预测主动段卫星测控信号质量的方法

通过建立卫星运动学模型,采用kalnmn滤波算法得到主动段卫星飞行弹道的最优估计以及卫星飞行姿态变化情况,利用其与卫星天线辐射方向图的对应关系,修正星地理论接收电平,最终实现主动段卫星姿态变化情;兄下,星地测控信号质量的预测,为地面决策指挥提『盐科学的信息支持。     

Understanding television's grade A and grade B service contours

The Grade A and Grade B service contours of a television broadcast station are used for a host of administrative purposes by the FCC including the regulation of CATV systems. Additionally, the contours are used by most stations for promotional and marketing purposes. The numerical values associated with these contours represent levels of field strength; consequently, assumptions were made in their determination as to noise limitation, the antenna gain, and transmission-line loss of the receiving system. Also, consideration was given to the subjective nature of the picture quality and the statistical variation of the field strength with time and location. The nature of these variables is discussed and the assumed values are tabulated in a format suitable for easy understanding and for analysis of possible future changes     

Understanding Television's Grade A and Grade B Service Contours

The Grade A and Grade B service contours of a television broadcast station are used for a host of administrative purposes by the FCC including the regulation of CATV systems. Additionally, the contours are used by most stations for promotional and marketing purposes. The numerical values associated with these contours represent levels of field strength; consequently, assumptions were made in their determination as to noise limitation, the antenna gain, and transmission-line loss of the receiving system. Also, consideration was given to the subjective nature of picture quality and the statistical variation of field strength with time and location. The nature of these variables is discussed and the assumed values are tabulated in a format suitable for easy understanding and for analysis of possible future changes.     

环焦式卫通天线波束宽度的一种新测试方法

在卫星通信系统中,卫通天线是其重要的组成部分,天线大部分采用环焦式卫通天线,3dB 波束宽度是环焦式卫通天线所有测试指标中比较重要的一项。本文主要探讨在某系统现有条件下对地球卫星站环焦式卫通天线 3dB 波束宽度指标的一种新的简单测试方法。     

关于乡镇模数转换的几点思考

目前全国的城市社区都已经普及了数字电视,但在一些偏远的乡镇,还在使用一些天线、卫星电视接收器等接收模拟电视节目。利用天线等接收设备,只能收看到为数不多的电视频道,在一些特别偏远的地区,甚至接收不到电视信号,更谈不上数字电视,为此就乡镇的模数转换进行讨论,并提出一些建议和想法。     

导航卫星跟踪体制及精度分析

采用卫星仿真工具包对全球卫星导航系统包括GPS、Galileo、Compass等导航卫星星座的地面站天线方位、俯仰跟踪特性进行了仿真分析,以大口径地面接收天线为例讨论了可行的地面站天线座架形式和跟踪体制.并综合常规卫星通信抛物面天线精度分析方法和测控雷达天线的精度分析方法对跟踪精度进行了系统的分析,分析结果可作为今后类...     

Study of the required crosspolar protection ratio in G-PAL TV FMsatellite transmissions planning

A study including simulation and a measurement campaign using live TV broadcast satellite signals and receiving commercial equipment has been carried out to investigate the required cross-polar protection ratio at the terrestrial receiving antenna for satellite transmission planning. This experiment provides useful and realistic results for efficient channel allocation in the spectrum band of broadcast satellite systems. Among them is the frequency offset required between cross-polar channels, depending on the cross-polar rejection at the receiving antenna, for a certain degree of video signal impairment due to the cross-polar channel interference effect, and taking into account the noise contribution to the signal. A worst case in frequency offset value, i.e., larger subjective impairment of the picture at equal carrier to noise ratio (CNR), has been detected around 5 MHz (near the chroma carrier in G-PAL system 4.43 MHz) only for high values of CNR. Different subjective degradation of the image due to cross-polar channel interference and noise has been observed, and their particular contributions to impairment have been evaluated     

Doppler spectrum in mobile-to-mobile communications in the presenceof three-dimensional multipath scattering

This paper provides analytical expressions for the time-autocorrelation function and the Doppler spectrum in a mobile radio channel in the presence of three-dimensional (3-D) multipath scattering. Mathematical modeling of the transmission channel is based on the assumption of wide-sense stationary (WSS) scattering. This paper deals with the case of a mobile-to-mobile radio link and derives formulas for the mobile-to-radiobase link as a special case. The Doppler spectrum examples provided are typical when assuming mobile terminal(s) located in densely built-up urban areas and simple dipole terminal antenna(s). Furthermore, the Doppler spectrum for transmission between a nongeostationary satellite and a mobile terminal located on the ground is analyzed. If different antenna patterns are to be considered and detailed knowledge is available on the multipath distribution, realistic Doppler spectra may be calculated using the approach presented in this paper     

Ground station antenna crosspolarisation measurements with an imperfectly polarised ancillary antenna

A technique has been described for measuring the crosspolarisation radiation patterns of linearly polarised, frequency reuse satellite ground station antennas, using a satellite as the remote source. This involves sampling of the imperfect satellite wave with a high polarisation purity ancillary antenna, and the application of a correction factor to the measured crosspolarisation levels. In practice, the ancillary antenna may have a small but finite crosspolarisation level, and error levels due to this are of interest. Error level expressions are given here, and some typical results are considered.