satellite communication system
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This document discusses satellite orbits and positioning systems. It begins by introducing satellite system components like subsystems, uplinks and downlinks. It then defines key terms related to satellite orbits, such as the minimum velocity needed to orbit Earth and different orbit classifications like LEO, MEO, HEO and polar orbits. Multiple access methods for satellites like TDMA, FDMA and CDMA are also covered. The document concludes by providing an overview of the GPS system and its space, control and user segments.
satellite communication system
- 1. By: Amjad Hassan Khan MK Lecturer in Electronics Kristu Jayanti College, Bengaluru
- 2. Introduction-satellite orbits, Satellite system; Block diagram, satellite sub systems, up link, down link, cross link, transponders (C, band) (Space content), ground station (simplified Block diagram of earth station). Multiple access methods -TDMA, FDMA, CDMA; GPS services like SPS and PPS.
- 4. Definitions and Terminology • For any object to be placed in an orbit around the Earth, it is essential for it to have a minimum velocity of 7.9 km/ sec • If you want to have a mission to the moon or beyond, or if you need to go beyond the gravitational attraction of earth, you will need to obtain a minimum speed of 11 km/sec • Once you get out of Earth’s gravity, you will continue to travel at that speed until you enter the gravitational attraction of another body.
- 5. Definitions and Terminology • When you are out in space, there will be no atmosphere to create any drag effects on your space vehicle • In order to escape Earth’s atmospheric effects, you have to be higher than 1000 km altitude. • The time taken by a satellite to execute one complete orbit is called the period and it is shown by τ
- 6. Period of a Satellite • The time taken by a satellite to execute one complete orbit is called the period and it is shown by τ. Hence, if a satellite rotates one orbit in 3 hours, then its period is 3 hours
- 7. • Elliptical orbits 1. LEO 2. MEO 3. HEO • Polar Orbits • Geostationary Satellite Orbit (GEO)
- 8. • LEO is Low Earth orbit and it is considered as 160 km to 500 km of altitude. Technically, in Low Earth orbit, the drag effects will always hinder operations. • Satellites in LEO will have very high speeds around 18,000 miles per hour
- 9. • MEO is Middle Earth Orbit is a special orbit that is beyond LEO. • MEO is usually defined as 500 Km – 1000 Km
- 10. • HEO is High Earth orbit • HEO is defined as orbit above 1000 km in most literature. It extends to 40,000 km altitude. • Mostly in HEO, the drag effects would be non existent. Hence, HEO will have a more stable orbit free from atmospheric effects, but also it will require much more energy to put there
- 11. • These orbits have an inclination near 90 degrees. This allows the satellite to see virtually every part of the Earth as the Earth rotates underneath it. It takes approximately 90 minutes for the satellite to complete one orbit.
- 20. Multiple access methods • Frequency Division Multiplexing (FDM) • Time Division Multiplexing (TDM) • Code Division Multiplexing (CDM) • Wavelength Division Multiplexing (WDM)
- 21. Time Division Multiplexing Access (TDMA)
- 22. Frequency Division Multiplexing Access (FDMA)
- 23. Code Division Multiplexing Access (CDMA)
- 25. Global Positioning system (GPS) • Space segment • Control segment • User segment
- 26. Space segment:
- 27. Control segment:
- 28. User Segment: