unit 3: satellite communications - wireless …...satellite communications link over a short...

Unit 3: Satellite CommunicationsWireless communications course

Ronal D. Montoya M.http://tableroalparque.weebly.com/radiocomunicaciones.html

ronalmontoya5310@correo.itm.edu.co

November 8, 2017

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Outline I

1. IntroductionOverview

2. ITU-R Satellite service frequency allocation and services

3. ITU-R Frequency band designations

4. Definitions and terms for earth-orbiting satellites

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Overview I

◦ The satellites are used for carry out any type of data inanalogue and digital formats.

◦ The satellites can form the star point of a simultaneouscommunications net linking together many users who may bewidely separated geographically.

◦ The satellites are capable to provide communications links toremote communities in sparsely populated areas which aredifficult to access by other means.

◦ The satellite signals ignore political boundaries as well asgeographic ones, which may or may not be a desirable feature.

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Overview II

◦ The cost of the ARSAT-1 (geostationary satellite fromArgentina) program was USD$ 250 million. It was developedand built in the INVAP factory in Bariloche, Argentina.

◦ A feature of any satellite system is that the cost is distanceinsensitive, meaning that it costs about the same to provide asatellite communications link over a short distance as it doesover a large distance.

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Overview III

◦ A satellite communication system is economical only where thesystem is in continuous use and the costs can be reasonablyspread over a large number of users (ARSAT-1 was developedfor a lifespan of 15 years, and it covers all the countries inSouth America).

◦ Satellites are also used for remote sensing (wheathermonitoring), scientific research, rescue and monitoring, militaryapplications, global positioning, among others.

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Overview IV

◦ Examaples of applications: INTELSAT (InternationalTelecommunications Satellite Organization), GPS (GlobalPositioning System), GLONASS (Global’naya NavigatsionnayaSputnikovaya Sistema), GALILEO (GNSS Global NavigationSatellite System), NOAA (U.S. National Oceanographic andAtmospheric Administration), etc...

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ARSAT-1

Figure: ARSAT-1, 24 transponders, Ku band (Argentina).

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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 thesouthwest Pacific.

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ITU-R Satellite service frequency allocation regions

Figure: ITU-R Satellite service frequency allocation regions.

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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 rescueservices (SARSAT).

◦ Meteorological satellite services: NOAA.

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ITU-R Frequency band designations I

Frequency band (GHz) Band designation0,1 - 0,3 VHF0,3 - 1,0 UHF

1 - 2 L2 - 4 S4 - 8 C8 - 12 X12 - 18 Ku18 - 27 K27 - 40 Ka

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ITU-R Frequency band designations II

Frequency band (GHz) Band designation40 - 75 V75 - 110 W110 - 300 mm300 - 3000 µ m

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Definitions and terms for earth-orbiting satellites I

◦ Apogee: The point farthest from earth (ha).

◦ Perigee: The point of closest approach to earth (hp).

◦ Line of apsides: the straight line joining the perigee and apogeethrough the center of the earth.

◦ Ascending node: The point where the oribit crosses theequatorial plane going from south to north.

◦ Descending node: The point where the oribit crosses theequatorial plane going from north to south.

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Definitions and terms for earth-orbiting satellites II

◦ Line of nodes: The line joining the ascending and descendingnodes through the center of the earth.

◦ Inclination: The angle between the orbital plane and theearth’s equatorial plane. It’s measured from the equator to theorbit in the ascending node direction, going from east to north(i). It will be seen as the greatest latitude, north or south.

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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

Definitions and terms for earth-orbiting satellites I

◦ Prograde orbit (direct orbit): An orbit in which the satellitemoves in the same direction as the earth’s rotation. Theinclination of a prograde orbit always lies between 0 and 90A◦.Most satellites are launched in a prograde orbit because theearth’s rotational velocity provides part of the orbital velocitywith a consequent saving in launch energy.

◦ Retrograde orbit: An orbit in which the satellite moves in adirection counter to the earth’s rotation. The inclination of aretrograde orbit always lies between 90 and 180A◦.

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Definitions and terms for earth-orbiting satellites II

◦ Argument of perigee: The angle from ascending node toperigee, measured in the orbital plane at the earth’s center, inthe direction of satellite motion.

◦ Mean anomaly: The average value of the angular position ofthe satellite with reference to the perigee. For a circular orbit,it gives the angular position of the satellite in the orbit. Forelliptical orbit, the position is much more difficult to calculate,and it’s used as an intermediate step in the calculation.

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Definitions and terms for earth-orbiting satellites III

◦ True anomaly: The true anomaly is the angle from perigee tothe satellite position, measured at the earth’s center. This givesthe true angular position of the satellite in the orbit as afunction of time.

◦ Azimuth: The vector from an observer (origin) to a point ofinterest is projected perpendicularly onto a reference plane; theangle 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 imaginarycelestial sphere. ”Above” means in the vertical directionopposite to the apparent gravitational force at that location.

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Definitions and terms for earth-orbiting satellites IV

◦ Nadir: The imaginary point directly ”below” on the imaginarycelestial sphere. ”Below” means in the vertical direction to theapparent gravitational force at that location.

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Definitions and terms for earth-orbiting satellites

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