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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,*,Technical English,For Information Science and Electronic Engineering,0,Unit 7,Satellite Communications,1,Part I,Applications of Communications satellite,2,New Words,abbreviate,缩略，简写成,geostationary orbit,对地静止轨道,elliptical orbit,椭圆轨道,complementary,互补的，补充的,submarine,海底的，潜水艇,relay,中继，接力,analogous,模拟的，类似的,disturbance,扰动，干扰,constellation,星座图，星罗棋布,geosynchronous,地球同步的,affiliate,会员，分支机构,limelight,众人注目的中心,diameter,直径,free-to-air TV,不加密不收费电视,headend,数据转发器,ambiguous,模糊的，混淆的,transponder,转发器，应答器,space-borne repeater,天空转发器,amateur,业余爱好，业余的,dialup,拨号,3,2,For fixed(point-to-point)services,communications satellites provide a technology complementary to that of fiber optic submarine communication cables.,They are also used for mobile applications such as communications to ships,vehicles,planes and hand-held terminals,and for TV and radio broadcasting,for which application of other technologies,such as cable,is impractical or impossible.,1,它们也可用于如船，车辆，飞机和手持终端的移动通信，用于电视和无线电广播，以及应用其它技术，比如电缆，是不现实或不可能的地方。,5,3 Telephony,The first and historically the most important application for communication satellites is in international telephony.,Fixed-point telephones relay calls to an earth station,where they are then transmitted to a geostationary satellite.,固定电话将通话传输到地面站，在那里再发射到对地静止卫星上,6,3,An analogous path is then followed on the downlink.,In contrast,mobile telephones(to and from ships and airplanes)must be directly connected to equipment to uplink the signal to the satellite,as well as being able to ensure satellite pointing in the presence of disturbances,such as waves onboard a ship.,2,相反，移动电话（船和飞机上接收和发送的）必须直接连到设备把信号上传到卫星，又能确保在有干扰时的卫星指向，如船上的电波干扰。,7,5 Satellite Television and radio,Television became the main market,its demand for simultaneous delivery of relatively few signals of large bandwidth to many receivers being a more precise match for the capabilities of geosynchronous comsats.,3,Two satellite types are used for North American television and radio:Direct Broadcast Satellite(DBS),and Fixed Service Satellite(FSS).,电视成为主要市场，其对相对很少的大带宽信号同时传送给很多接收机的要求更好地匹配了对地静止通信卫星的性能。,9,6,A direct broadcast satellite is a communications satellite that transmits to small DBS satellite dishes,(usually 18 to 24inches in diameter).Direct broadcast satellites generally operate in the upper portion of the microwave Ku band.DBS technology is used for DTH-oriented(Direct-To-Home)satellite TV services.,直播卫星是一种通信卫星，它直接向小型,DBS,卫星天线发射。,10,8,FSS satellites differ from DBS satellites in that they have a lower RF power output than the latter,requiring a much larger dish for reception,(3 to 8feet in diameter for Ku band,and 12feet on up for C band),as well as using linear polarization for each of the transponders RF input and output,(as opposed to circular polarization used by DBS satellites),.,5,FSS,与,DBS,的不同之处在于固定业务卫星具有更低的射频功率输出，需要更大的碟形卫星接收天线，收发器的射频输入和输出也都采用线极化。,12,9,This all changed when the first American DBS provider,DirecTV,was established in 1994,stealing the limelight from FSS satellite technology for DTH programming,.However,FSS satellites on the C and Ku bands are still used by cable and satellite channels such as CNN,The Weather Channel,HBO and others,for distribution to cable TV headends,and to the DBS providers themselves who then re-distribute these channels over their own DBS systems.,夺去了,FSS,卫星技术在,DTH,节目方面的风头,14,10,Free-to-air satellite TV channels are also usually distributed on FSS satellites in the Ku band.The Intelsat Americas 5,Galaxy 10R and AMC 3 satellites over North America,provide a quite large amount of FTA channels,on their Ku band transponders,.,在他们的,Ku,波段收发器上提供相当多的,FTA,频道。,15,12,The definitions of FSS and DBS satellites outside of North America,especially in Europe,are a bit more ambiguous.,Most satellites used for direct-to-home television in Europe have the same high power output as DBS-class satellites in North America,but use the same linear polarization as FSS satellites.,Because of this,the terms FSS and DBS are more so used throughout the North American continent,and are uncommon in Europe.,欧洲大部分用于直播的卫星使用与北美,DBS,级同样级别的功率输出，却使用与,FSS,卫星一样的线性极化。,17,13 Amateur radio,Amateur radio operators have access to the OSCAR satellites that have been,designed specifically to carry amateur radio traffic,.Most such satellites operate as space-borne repeaters,and are,generally accessed by amateurs equipped with UHF or VHF radio equipment and highly directional antennas such as Yagi or dish antennas,.,被设计成承载业余无线电通信流量,通常被装备,UHF,或,VHF,设备并使用高度方向性天线如八木天线或抛物面天线的业余无线电接入,18,13,Due to the limitations of ground-based amateur equipment,most amateur satellites are launched into fairly low Earth orbits,and are designed to deal with only a limited number of brief contacts at any given time,.Some satellites also provide,data-forwarding services,using the AX.25 or similar protocols.,大多数业余卫星发射到低地轨道上，并设计得只能在任何给定时刻进行有限次数的简短接触。,数据转发业务,19,14 Satellite broadband,After the 1990s,satellite communication technology has been used as a means to connect to the Internet via broadband data connections.This can be very useful for users who are,located in very remote areas,and cannot access a wireline broadband or dialup connection,.,位于边远地区，不能接入有线宽带网络或拨号上网。,20,Part II,Satellite Internet access,21,New Words,terms of contract,合同条款,bolt,用螺栓固定住,cost effective,经济的，合算的,surf,冲浪，浏览网络,authentication,认证,stack,堆栈,latency,延迟，潜伏期,asymmetry,不对称,encrypt,加密,accessible,可访问的，可用的,rain fade,降雨衰减,bidirectional,双向的,sponsor,支持，赞助，资助,architecture,结构，建筑,23,1,Satellite Internet services are used in locations where terrestrial Internet access is not available and in locations which move frequently.Internet access via satellite is available worldwide,including vessels at sea and mobile land vehicles.,There are three types of satellite Internet service:one-way multicast,one-way with terrestrial return,and very small aperture terminal(VSAT)(two-way)satellite access.,1,有三种卫星因特网服务：单向多播卫星接入，地面回传单向卫星接入和甚小口径（天线）终端（双向）卫星接入。,24,2 One-way multicast,One-way multicast satellite Internet systems are used for Internet Protocol(IP)multicast-based data,audio and video distribution.,In the U.S.,a Federal Communications Commission(FCC)license is required only for the uplink station and no license is required for users.Note that,most Internet protocols will not work correctly over one-way access,since they require a return channel.,单向多播卫星系统用于,IP,多播数据、音频、视频的发布,大多数互联网协议不能在单向接入情况下正常工作，因为它们要求一个回馈信道,25,3,System hardware components:Similar to one-way terrestrial return,satellite Internet access may include interfaces to the public switched telephone network for squawk box applications,.An Internet connection is not required,but,many applications include a Protocol(FTP)server to queue data for broadcast,.,卫星互联网接入可包括与公共交换电话网之间的接口用于内部通话。,许多应用包括一个,FTP,服务器以将待广播的数据排成队列。,27,4,System software components:Most one-way multicast applications require custom programming at the remote sites.,The software at the remote site must filter,store,present a selection interface to and display the data.,2,The software at the transmitting station must provide,access control,priority queueing,sending,and encapsulating of the data,.,远端的软件必须对数据进行过滤、存储、提供选择界面并显示。,数据的接入控制、按优先级形成队列、发送、封装,28,6 System hardware components,The transmitting station(also called teleport,head end,uplink facility,or hub)has two components:,30,6,Internet connection:The ISPs routers connect to,proxy servers,which can,enforce,quality of service,(QoS)bandwidth limits and guarantees for user traffic,.These are then connected to a DVB,encapsulator,which is then connected to a,DVB,-S modem.,The,radio frequency,(RF)signal from the DVB-S modem is connected to an up converter which is connected via,feed line,to the outdoor unit.,3,对用户流量实行并保证,QoS,带宽限制,来自,DVB-S,调制解调器的射频信号连接到上变频器，上变频器通过馈线连接到室外单元。,31,6,Satellite uplink:The,block,upconverter,(BUC)and optional,low-noise block converter,(LNB),which may,use a,waveguide,to connect to the optional,orthomode,transducer,(OMT)which is bolted to the,feed horn,which is connected by metal supports to the,satellite dish,and mount,.,用波导联到一个接在馈电喇叭上的可选直接式收发转换器，它被用金属支撑安装在卫星天线和支架上。,32,7,At the remote location(Earth station)the setup consists of:,Outdoor unit(satellite dish with mount,feed horn,universal LNB for,Ku band,and feed line),Indoor unit(DVB-S,Peripheral Component Interconnect,card inside a computer,or DVB external modem connected to a computer via an,Ethernet,port or USB port),33,8,Depending on the providers terms of contract,one cost effective way to use one-way satellite internet is to use General Packet Radio Service(GPRS)for the back-channel.,By utilizing a 9600 bit/s connection that is offered in standard GPRS,the upload volume is very low,and since this service is not per-time charged,but charged by volume uploaded,users are able to surf and download in broadband speeds.,4,通过使用标准,GPRS,提供的,9600bps,连接，上传量很小。此外由于该项业务不是按时间计费，而是按上传数据流量计费的，用户可以宽带速度进行浏览和下载。,34,8,There are companies offering speed up to 24 Mbit/s.,Another view of using GPRS as return would be the mobility when the service is provided by a satellite that transmits in the field of 50 to 53 dBW.,Using a 33 cm wide satellite dish,a notebook and a normal GPRS equipped GSM phone,users can get broadband everywhere.,用,GPRS,作为回传的另一个理由是由卫星提供业务时的机动性，卫星发射场在,50dBW,到,53dBW,之间。,The,Decibel watt,or,dBW,is a unit for the measurement of the strength of a signal expressed in decibels relative to one watt.,35,9 System software components,Remote sites require a minimum of programming to provide authentication and set proxy server settings.,Filtering is usually provided by the DVB card driver.,远程节点在提供认证和设置代理服务器时要求最少的编程,36,10,Often,non-standard IP stacks are used to address the latency and asymmetry problems of the satellite connection,.Data sent over the satellite link is generally encrypted,as otherwise it would be accessible to anyone with a satellite receiver.,用非标准,IP,堆栈解决卫星连接中的潜伏期和非对称问题。,37,11,Many IP-over-satellite implementations use paired proxy servers at both endpoints so that clients and servers do not need to accept the latency inherent in a satellite connection.,5,许多卫星,IP,的实现在终端使用成对的代理服务器，这样客户端和服务器就不必承受卫星连接中固有的延迟。,38,11,For similar reasons,there exist special Virtual Private Network(VPN)implementations designed for use over satellite links because standard VPN software cannot handle the long packet travel times.,39,12,Upload speeds are limited by the users dial-up modem,and latency is high,as it is for any satellite based Internet.,Download speeds can be very fast compared to dial-up:1Mbit/s,4Mbit/s,and 16Mbit/s packages are generally offered.,上传速度受制于用户的拨号,modem,，延迟量很大，对任何基于卫星的互联网业务都是如此。,40,13 Theory of operation,The back panel of a satellite modem,with coaxial connections for both incoming and outgoing signals,and an Ethernet port for connection to the internal network.,41,14,Remote sites use the proxy server at the earth station,which is configured to route all outbound traffic to the QoS server,which makes sure no user exceeds the allotted bandwidth or monthly traffic limits.,6,Traffic is then sent to the encapsulator,which puts the IP packets inside of DVB packets.The DVB packets are then sent to the DVB modem and then to the transmitter.,在地面发送站远地使用代理服务器，其设定为向服务质量服务器发送所有的外传数据，服务质量服务器确保用户不超过分配带宽或每月的通信流量限制。,42,15 Two-way,Two-way satellite Internet service sends data from remote sites via satellite to a hub,which then sends the data to the Internet.,The satellite dish at each location must be precisely positioned to avoid interference with other satellites.The oscillators in some radar detectors can cause interference with these systems.,双向卫星业务通过卫星向,Hub,传送数据，,Hub,又将数据传向卫星。,43,15,Also,each location must use power management to adjust the amount of transmit power,to compensate for things like rain fade,.There are several types of two way satellite Internet services,such as time division multiple access(TDMA)or single channel per carrier(SCPC).,补偿像降雨衰落这样的情况,44,16,Each remote location is also equipped with a telephone modem;the connections for this are as with a conventional dial-up ISP.,Two way satellite systems may sometimes use the modem channel in both directions for data where latency is more important than bandwidth,reserving the satellite channel for download data where bandwidth is more important than latency,such as for.,双向卫星系统当延迟比带宽更重要时在两个方向均会使用,modem,信道传输数据，而为下载保留卫星信道，因为此时带宽比延迟更重要，例如对于文件传输。,45,17,Uplink speeds rarely exceed one megabit per second and latency can be up to one second.Satellite phone services also provide data services at the comparatively slow speed of 2400bit/s.,46,18,International Mobile Satellite Organization(INMARSAT)offers three bidirectional satellite internet services called Broadband Global Area Network(BGAN),Regional BGAN and MPDS,neither of which has to be precisely aligned but the speeds are lower than the dish-based systems and bandwidth costs are much higher.,7,BGAN has the highest data rate.,国际移动卫星组织提供了三种双向卫星因特网服务：宽带全球局域网、宽带全球区域网和移动包数据交换业务，它们都不需精确地调整，但速度要比基于碟形卫星天线的系统低，而且带宽花费也更大。,47,19,In 2006 the European Commission sponsored the UNIC project which aims at,developing an end-to-end scientific test bed for the distribution of new broadband interactive TV-centric services delivered over low-cost two-way satellite to actual end-users in the home,.The UNIC architecture employs DVB-S2 standard for downlink and DVB-RCS standard for uplink.,发展一个端到端的科学测试基地，用于通过低成本双向卫星将新型宽带交互式电视中心服务传送到真正的家庭终端用户。,48,
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