Chapter17SatelliteServices第十七章卫星通讯服务亚洲大学资讯工程

1、Chapter 17. Satellite Services第十七章 衛星通訊服務亞洲大學資訊工程學系碩士班呂克明教授二七年一月八日 7/26/20221Chapter 17. Satellite Services(第十七章衛星通訊服務)Introduction (緒言)Satellite Mobile Services (衛星移動服務)VSATs (小型地球站)Radarsat (雷達衛星)Global Positioning Satellite System (全球衛星定位系統)Orbcomm (低軌雙向呼叫器衛星通訊系統)Homework Problems (習題)7/26/20222I

2、ntroduction(緒言)Direct broadcast satellite (DBS, 直播衛星通訊服務) direct-to-home broadcastingVery small aperture terminals (VSAT,小型地球站) business applicationsMobile satellite service (MSAT,衛星移動服務) mobile communications for vehicles, ships and aircraft.Radarsat (雷達衛星) provide environmental monitoring services

3、Global Positioning Satellite (GPS,全球衛星定位系統) system non-geostationary for survey and position location generally.7/26/20223Satellite Mobile Services(衛星移動服務)Asian Cellular System- AceS utilzes one Garuda geostationary satellite covering the Asia Pacific area. A second satellite will be employed to exp

4、and the service into western and central Asia, Europe, and northern Africa. Each satellite has capacity for at least 11,000 simultaneous telephone channels, servicing up to 2 million subscribers.Ellipso- Ellipso (MEO) is designed on the basis that the population density to be served is concentrated

5、in the northern hemisphere, with very low population density below 50 degree s latitude.7/26/20224Satellite Mobile Services(衛星移動服務)(continued)Globalstar Globalstar employs 48 satellites in circular earth orbits (LEO) in eight planes at a height of 1414 km.MSAT- covers the primary service area of Can

6、ada and the US.New ICO- New ICO (12 MEO satellites).Thuraya- Thuraya satellite is in geostationary orbit located at 44 degree and serving an area between 20 degree W to 100 degree longitude and 60 degree N to 2 degree S latitude. A 12.25 x 16 m antenna is employed providing 250 to 300 spot beams, wi

7、th onboard beam-switching.7/26/20225VSAT (小型地球站)VSAT antennas sizes are between 1.5 m and 2.4 m.VSAT in either C-band or Ku-bandPopular access method is frequency-division multiple access (FDMA) which allows the use of comparatively low-power VSAT terminals.Time-division multiple access (TDMA) also

8、can be used but is not efficient for low-density uplink traffic from the VSAT.7/26/20226VSAT (小型地球站) (continued)A form of demand-assigned multiple access (DAMA) is employed in some systems in which channel capacity is assigned in response to the fluctuating demands of the VSATs in the network.DAMA c

9、an be used with FDMA and TDMA.In 1990, Abramson presents a method of code-division multiple access (CDMA) using spread spectrum techniques, coupled with the Aloha protocol.7/26/20227VSAT (小型地球站)(continued)VSAT star configuration and mesh configurationKa-band covers 27 to 40 GHz. In Hughes, 1993, res

10、ults are presented for frequencies of 18.7 and 28.5 GHz.The major shortcomings of present VSAT systems are the high initial costs, the tendency toward optimizing systems for large networks, and the lack of direct VSAT-to-VSAT links.7/26/20228Radarsat(雷達衛星)Radarsat is an earth-resources remote-sensin

11、g satellite which is part of the Canadian space program.The objectives of the Radarsat program are:Resource management and maritime safetyDevelop, launch, and operate an earth observation satellite with synthetic aperture radar (SAR)Establish a Canadian mission control facilityMarket Radarsat data g

12、lobally through a commercial distributorMake SAR data available for researchMap the whole world with stereo radarMap Antarctica in two seasons7/26/20229Radarsat(雷達衛星) (Continued)Applications (雷達衛星之應用):Shipping and fisheries (海運與漁業)Ocean feature mapping (海洋特性探勘)Oil pollution monitoring (油污染監測)Sea ice

13、 mapping (海洋浮冰探勘) Iceberg detection (冰山偵測)Crop monitoring (農業監測)Forest management (森林管理)Geological mapping (水利勘輿) Topographic mapping (地形勘輿)Land use mapping (陸上勘輿)7/26/202210Global Positioning Satellite System(全球衛星定位系統)GPS system is a constellation of 24 satellites circles the earth in 6 near-circul

14、ar inclined orbits, at an altitude of approximately 20,000 km. Please refer to /gov/geography/gcraft/notes/gps/gps_f.htmlBy receiving signals from at least four (4) of these satellites, the receiver position (latitude, longitude, and altitude) and time can be determined accurately.Time enters into the position determination in two (2) ways.7/26/202211Orbcomm (低軌雙向呼叫器衛星通訊系統)Orbcomm is a low earth orbiting (LEO) satellite system. The system consists of 24 low orbiting satellites intended to provide economic two-way message and data communications services and position determ