Prepared by Dr. Mohammed Taha El Astal

Transcription

1 9/2/ Prepared by Dr. Mohammed Taha El Astal EELE 6335 Telecom. System Part I: Satellite Communic ations Winter Content 1.1 Introduction, Sat-Com Why? 1.2 Frequency Allocations for Satellite services. 1.3 INTELSAT 1.4 U.S. DOMSAT 1.5 Polar Orbiting Satellites 1.6 Argos System 1

2 9/2/ 1.1 Introduction: Sat-Com. features, why? 1. Very large coverage areas, hence: the sat. can be a star point of a comm. Network that is simultaneously linking many users who may be widely separated geographically. Provide links to remote communities in sparsely populated areas that are difficult to access by other means. 1.1 Introduction: Sat-Com. features, why? This overcome the need of lot of repeaters needed two connect faraway locations. Why, you need lot of repeaters to link two points wirelessly(microwave frequencies)? Earth is a sphere The microwave frequencies travel in straight line Hence, to connect two regions very far away on the two side of the sphere, you need a lot of repeaters because of earth's curvature. 2

3 9/2/ 2. Sat.-Com. ignore political boundaries & geographical boundaries. 3. Sat.-Com. cost is distance insensitive. Canadian Anik-E1 (1994)=281.2M$ Canadian Anik-E2 (1996)=290.5M$ 3

4 9/2/ 4. Satellites can be used for remote sensing Landsat image of the Betsiboka River, Madagascar using bands 3, 2, and 1 to highlight the complex delta features. Using this non-traditional, 'remote sensing' approach to seismic interpretation can reveal spatial detail in geologic heterogeneity that is beyond classic seismic resolution. Source: NASA 1.2 Frequency Allocations for Satellite Services: Frequency allocation is responsibility of ITU This is to ensure that : Non-interference condition between different satellite systems Fairness between nations in access to the satellite frequencies Frequency allocation may be exclusive for given service. shared between services. Service provisioning usually requires consent of all countries within coverage area of the satellite ITU Regions Example: VIASAT license in Ka band as of

5 9/2/ Satellite Services classified according to ITU into : Broadcast satellite services Earth exploration services (ESS) Navigation satellite services Space research services (SRS) N.B. Also, Space operations services (SOS), Radio determination satellite services (RSS), and Inter-satellite services (ISS) Satellites operate in microwave frequency range. Majority operates in C and Ku. Two links Uplink ground to sat. Downlink sat. to ground Each link uses its own band. Uplink operates on higher frequency, why? (later) It is common practice to: UL=6 and DL=4 6/4 GHz. 14,030 & 11,730 14/12 GHz 5

6 9/2/ 1.3 INTELSAT INTELSAT: International Telecommunication Satellites Created in 1964, now has 140 member countries and >40 investing entities. Interactive coverage map: etmaps/ Additionally, It has a huge fiber-optic network too. ist=plg54ku_rt7fwpzgnhjpt60qprpvs1giam 6

7 9/2/ These Satellite are in geostationary orbit, meaning? It means that Can be identified using Telescope by: Specified by its longitude 7

8 9/2/ Footprint of INTELSAT satellite 905, positioned at east longitude Figure 1.2 INTELSAT satellite 905 is positioned at E longitude. (a) The footprints for the C-band antennas; (b) the Kuband spot 1 beam antennas; and (c) the Ku-band spot 2 beam antennas Global, spot beam antennas, explain? Global beam antenna: all visible are is covered. However, this means it received in very weak signal strength level (mean large Rx antenna is needed) even if high power is transmitted. Thus, spot beam antenna is installed too to cover and focus on part of the visible area (multi-antennas or steering can be used to turn the coverage to another area) INTELSAT (few days ago:22/8/) 8

9 9/2/ Located at 60 E co-located with Intelsat 20 at 68.5 E INTELSAT (few days ago:25/8/) Full launch video here 9

10 9/2/ 1.4 U.S. DOMSAT DOMSAT: Domestic Satellites. Provide various telecomm services (voice, data, and video) within a country. U.S. DOMSAT satellites that are used for DTH are classified to : All U.S. DOMSAT are suited in geostationary orbit. What is the suitable spacing? FCC (1996) adopts, why? : 2 for 6/4 & 1.5 for 14/12, mean 180. Now, 1/10 (=73Km) is adopted, mean <3600 satellites can be located. Currently, there is 429 (16/8/) N.B: 60 to 37 mean nearly 1:200, this mean smaller antenna is required 1.5 Polar Orbiting Satellites Polar orbiting Satellites orbit the earth in such a way as to cover the north and south polar regions Whereas there is only 1 geostationary orbit, there are (in theory) an infinite # of polar orbits 10

11 9/2/ km: known as LEO /LEOSAT Generally, used in weather and environmental studies & search and rescue operations. Have a footprint about 6000 km in a diameter (the size of the antenna spot beam on the earth s surface ). The orbital period =102 min How many orbits/day? Day=1440 min 14 orbits/day What is the shift/orbit (in degree)? shift=360*102/1440=25 /orbit 6000Km 1.6 ARGOS System The Argos data collection system (DCS) collects environmental data radioed up from platform transmitter terminals (PTT). PTT can be fixed/drifting buoys, balloons and animals. Varies from 17g to more depend on applications. =sp3oqxuz_gq Transmitting at preset intervals and those in 6000 Km swath are received by Satellite. Argus Panoptes (or Argos) is a 100-eyed giant in Greek mythology. 11

12 322Km 9/2/ As mentioned, the satellite complete about 14 orbits/day and all orbits cross overt he poles. Case 1 (MAX): in the region of poles, this PTT can TX/RX with the SAT 14 times daily. At least, 2 satellites are operational at any time, this double # to 28 daily. Case 2 (MIN): in the region of equator: this PTT can communicate with the satellite 3-4 times daily. 7 times daily if 2 satellites are operational. Show? Earth radius =6378 Km, then its circumference =40,074Km. Each orbit move nearly 40074*25.5/360=2839Km atch?v=y_jm_bxqgve Please try to check this: Km 3161Km Argos uses Doppler shift in the frequency received at the satellite is used to determine the location of the PTT (2007). V. important concept : f = (1 + v c )f 0 Case 1 : approaching v + +, f > f 0 Case 2: moving faraway v, f < f 0 4OnBYrbCjY 12

13 9/2/ Dr. Mohammed Taha El Astal 29/8/ 13