Unit 3: Satellite Communications

Transcription

1 Unit 3: Satellite Communications Wireless communications course Ronal D. Montoya M. November 8, /20

2 Outline I 1. Introduction Overview 2. ITU-R Satellite service frequency allocation and services 3. ITU-R Frequency band designations 4. Definitions and terms for earth-orbiting satellites 2/20

3 Overview I The satellites are used for carry out any type of data in analogue and digital formats. The satellites can form the star point of a simultaneous communications net linking together many users who may be widely separated geographically. The satellites are capable to provide communications links to remote communities in sparsely populated areas which are difficult to access by other means. The satellite signals ignore political boundaries as well as geographic ones, which may or may not be a desirable feature. 1. Introduction 3/20

4 Overview II The cost of the ARSAT-1 (geostationary satellite from Argentina) program was USD$ 250 million. It was developed and built in the INVAP factory in Bariloche, Argentina. A feature of any satellite system is that the cost is distance insensitive, meaning that it costs about the same to provide a satellite communications link over a short distance as it does over a large distance. 1. Introduction 4/20

5 Overview III A satellite communication system is economical only where the system is in continuous use and the costs can be reasonably spread over a large number of users (ARSAT-1 was developed for a lifespan of 15 years, and it covers all the countries in South America). Satellites are also used for remote sensing (wheather monitoring), scientific research, rescue and monitoring, military applications, global positioning, among others. 1. Introduction 5/20

6 Overview IV Examaples of applications: INTELSAT (International Telecommunications Satellite Organization), GPS (Global Positioning System), GLONASS (Global naya Navigatsionnaya Sputnikovaya Sistema), GALILEO (GNSS Global Navigation Satellite System), NOAA (U.S. National Oceanographic and Atmospheric Administration), etc Introduction 6/20

7 ARSAT-1 Figure: ARSAT-1, 24 transponders, Ku band (Argentina). 1. Introduction 7/20

8 ITU-R Satellite service frequency allocation Region 1: Europe, Africa, what was formerly the Soviet Union, and Mongolia. Region 2: North and South America and Greenland. Region 3: Asia (excluding region 1 areas), Australia, and the southwest Pacific. 2. ITU-R Satellite service frequency allocation and services 8/20

9 ITU-R Satellite service frequency allocation regions Figure: ITU-R Satellite service frequency allocation regions. 2. ITU-R Satellite service frequency allocation and services 9/20

10 ITU-R ITU-R Satellite services Fixed satellite service (FSS). Broadcasting satellite service (BSS): DBS, DTH, etc. Mobile satellite services: land mobile, maritime mobile, aeronautical mobile. Navigational satellite services: GNSS, search and rescue services (SARSAT). Meteorological satellite services: NOAA. 2. ITU-R Satellite service frequency allocation and services 10/20

11 ITU-R Frequency band designations I Frequency band (GHz) Band designation 0,1-0,3 VHF 0,3-1,0 UHF 1-2 L 2-4 S 4-8 C 8-12 X Ku K Ka 3. ITU-R Frequency band designations 11/20

12 ITU-R Frequency band designations II Frequency band (GHz) Band designation V W mm µ m 3. ITU-R Frequency band designations 12/20

13 Definitions and terms for earth-orbiting satellites I Apogee: The point farthest from earth (h a ). Perigee: The point of closest approach to earth (h p ). Line of apsides: the straight line joining the perigee and apogee through the center of the earth. Ascending node: The point where the oribit crosses the equatorial plane going from south to north. Descending node: The point where the oribit crosses the equatorial plane going from north to south. 4. Definitions and terms for earth-orbiting satellites 13/20

14 Definitions and terms for earth-orbiting satellites II Line of nodes: The line joining the ascending and descending nodes through the center of the earth. Inclination: The angle between the orbital plane and the earth s equatorial plane. It s measured from the equator to the orbit in the ascending node direction, going from east to north (i). It will be seen as the greatest latitude, north or south. 4. Definitions and terms for earth-orbiting satellites 14/20

15 Definitions and terms for earth-orbiting satellites Figure: Definitions and terms for earth-orbiting satellites. 4. Definitions and terms for earth-orbiting satellites 15/20

16 Definitions and terms for earth-orbiting satellites I Prograde orbit (direct orbit): An orbit in which the satellite moves in the same direction as the earth s rotation. The inclination of a prograde orbit always lies between 0 and 90Â. Most satellites are launched in a prograde orbit because the earth s rotational velocity provides part of the orbital velocity with a consequent saving in launch energy. Retrograde orbit: An orbit in which the satellite moves in a direction counter to the earth s rotation. The inclination of a retrograde orbit always lies between 90 and 180Â. 4. Definitions and terms for earth-orbiting satellites 16/20

17 Definitions and terms for earth-orbiting satellites II Argument of perigee: The angle from ascending node to perigee, measured in the orbital plane at the earth s center, in the direction of satellite motion. Mean anomaly: The average value of the angular position of the satellite with reference to the perigee. For a circular orbit, it gives the angular position of the satellite in the orbit. For elliptical orbit, the position is much more difficult to calculate, and it s used as an intermediate step in the calculation. 4. Definitions and terms for earth-orbiting satellites 17/20

18 Definitions and terms for earth-orbiting satellites III True anomaly: The true anomaly is the angle from perigee to the satellite position, measured at the earth s center. This gives the true angular position of the satellite in the orbit as a function of time. Azimuth: The vector from an observer (origin) to a point of interest is projected perpendicularly onto a reference plane; the angle between the projected vector and a reference vector (north) on the reference plane is called the azimuth. Zenith: The imaginary point directly above on the imaginary celestial sphere. Above means in the vertical direction opposite to the apparent gravitational force at that location. 4. Definitions and terms for earth-orbiting satellites 18/20

19 Definitions and terms for earth-orbiting satellites IV Nadir: The imaginary point directly below on the imaginary celestial sphere. Below means in the vertical direction to the apparent gravitational force at that location. 4. Definitions and terms for earth-orbiting satellites 19/20

20 Definitions and terms for earth-orbiting satellites Figure: Definitions and terms for earth-orbiting satellites. 4. Definitions and terms for earth-orbiting satellites 20/20