信息科学与电子工程专业英语Lecture07

1、EE141 电子信息科学概论MTI 2011 Aifeng Ren电子信息科学概论11任爱锋任爱锋电子工程学院电子工程学院 E-mail: Office: 新科技楼A901 Phone: 88202830-607 Mobile:E141 2011 Aifeng Ren电子信息科学概论2 电子信息科学概论MTI2 Unit 7-1 通信卫星的应用通信卫星的应用EE141 2011 Aifeng Ren电子信息科学概论3 电子信息科学概论MTI3abbreviate 缩略，简写成geostationary orbit 对地静止轨道elliptical orbit 椭圆轨道

2、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EE141 2

3、011 Aifeng Ren电子信息科学概论4 电子信息科学概论MTI4A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in space for the purposes of telecommunications. Modern communications satellites use a variety of orbits including geostationary orbits, elliptical orbits and low (p

4、olar and non-polar) Earth orbits.Unit 7-1 通信卫星的应用EE141 2011 Aifeng Ren电子信息科学概论5 电子信息科学概论MTI5For 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 comm

5、unications 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.1Unit 7-1 通信卫星的应用EE141 2011 Aifeng Ren电子信息科学概论6 电子信息科学概论MTI6The first and historically the most important applica

6、tion 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. Unit 7-1 通信卫星的应用电话（Telephony）EE141 2011 Aifeng Ren电子信息科学概论7 电子信息科学概论MTI7An analogous path is then followed on the dow

7、nlink. 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.2Unit 7-1 通信卫星的应用电话（Telephony）EE141

8、2011 Aifeng Ren电子信息科学概论8 电子信息科学概论MTI8Improvements in submarine communications cables caused a decline in the use of satellites for fixed telephony in the late 20th century. Hand held telephones (cellular phones) used in urban areas do not make use of satellite communications. Instead they have acces

9、s to a ground based constellation of receiving and retransmitting stations.Unit 7-1 通信卫星的应用电话（Telephony）EE141 2011 Aifeng Ren电子信息科学概论9 电子信息科学概论MTI9Television became the main market, its demand for simultaneous delivery of relatively few signals of large bandwidth to many receivers being a more preci

10、se 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). Unit 7-1 通信卫星的应用卫星电视和无线电台（Satellite Television and radio ）EE141 2011 Aifeng Ren电子信息科学概论10 电子信息科学概论MTI10

11、A direct broadcast satellite is a communications satellite that transmits to small DBS satellite dishes (usually 18 to 24 inches 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) satelli

12、te TV services. Unit 7-1 通信卫星的应用卫星电视和无线电台（Satellite Television and radio ）EE141 2011 Aifeng Ren电子信息科学概论11 电子信息科学概论MTI11Fixed Service Satellites (FSS) use the C band, and the lower portions of the Ku bands. They are normally used for broadcast feeds to and from television networks and local affiliate

13、 stations, as well as being used for distance learning by schools and universities, business television, videoconferencing, and general commercial telecommunications.4 FSS satellites are also used to distribute national cable channels to the central control units. Unit 7-1 通信卫星的应用卫星电视和无线电台（Satellite

14、 Television and radio ）EE141 2011 Aifeng Ren电子信息科学概论12 电子信息科学概论MTI12FSS 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 8 feet in diameter for Ku band, and 12 feet on up for C band), as well as using li

15、near polarization for each of the transponders RF input and output (as opposed to circular polarization used by DBS satellites).5 Unit 7-1 通信卫星的应用卫星电视和无线电台（Satellite Television and radio ）EE141 2011 Aifeng Ren电子信息科学概论13 电子信息科学概论MTI13FSS satellite technology was also originally used for DTH satellite

16、 TV from the late 1970s to the early 1990s in the United States in the form of TVRO (TeleVision Receive Only) receivers and dishes.Unit 7-1 通信卫星的应用卫星电视和无线电台（Satellite Television and radio ）EE141 2011 Aifeng Ren电子信息科学概论14 电子信息科学概论MTI14This all changed when the first American DBS provider, DirecTV, wa

17、s 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 provid

18、ers themselves who then re-distribute these channels over their own DBS systems.Unit 7-1 通信卫星的应用卫星电视和无线电台（Satellite Television and radio ）EE141 2011 Aifeng Ren电子信息科学概论15 电子信息科学概论MTI15Free-to-air satellite TV channels are also usually distributed on FSS satellites in the Ku band. The Intelsat America

19、s 5, Galaxy 10R and AMC 3 satellites over North America provide a quite large amount of FTA channels on their Ku band transponders.Unit 7-1 通信卫星的应用卫星电视和无线电台（Satellite Television and radio ）EE141 2011 Aifeng Ren电子信息科学概论16 电子信息科学概论MTI16The American Dish Network DBS service has also used FSS technology

20、 due to their need for more capacity to carry local television stations, and for more bandwidth to carry HDTV channels. Satellites for communication have now been launched that have transponders in the Ka band. NASA as well has launched experimental satellites using the Ka band recently.Unit 7-1 通信卫星的应