Satellites orbits Lec - 10 4/23/2017 Dr. Hassan Yousif

Satellites orbits Satellite Orbits GEO LEO MEO HEO HAPs LEO 500 -1000 km GEO 36,000 km MEO 5,000 – 15,000 km Satellite Orbits GEO LEO MEO HEO HAPs (High Altitude Platform ) 4/23/2017 Dr. Hassan Yousif

Geostationary Earth Orbit (GEO) These satellites are in orbit 35,863 km Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates. This means GEO satellites remain in the same position relative to the surface of earth. 4/23/2017 Dr. Hassan Yousif

Low Earth Orbit (LEO) LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to 1,500 km above the surface. LEO satellites don’t stay in fixed position relative to the surface, and are only visible for 15 to 20 minutes each pass. A network of LEO satellites is necessary for LEO satellites to be useful 4/23/2017 Dr. Hassan Yousif

Low Earth Orbit (LEO) 4/23/2017 Dr. Hassan Yousif

4/23/2017 Dr. Hassan Yousif

LEO (cont.) Disadvantages A network of LEO satellites is needed, which can be costly LEO satellites have to compensate for Doppler shifts cause by their relative movement. Atmospheric drag effects LEO satellites, causing gradual orbital deterioration. 4/23/2017 Dr. Hassan Yousif

LEO (cont.) 4/23/2017 Dr. Hassan Yousif

Doppler Shift 4/23/2017 Emergency locator Terminal Dr. Hassan Yousif

Medium Earth Orbit (MEO) A MEO satellite is in orbit 8,000 km -18,000 km MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours. MEO satellites have a larger coverage area than LEO satellites. A.k.a. Intermediate Circular Orbits (ICO), 4/23/2017 Dr. Hassan Yousif

Highly Elliptical Orbit (HEO) Known as Molniya Orbit Satellites Used by Russia for decades. Molniya Orbit is an elliptical orbit. The satellite remains in a nearly fixed position relative to earth for eight hours. A series of three Molniya satellites can act like a GEO satellite. Useful in near polar regions. 4/23/2017 Dr. Hassan Yousif

Highly Elliptical Orbit (HEO) 4/23/2017 Dr. Hassan Yousif

Other Orbits (cont.) High Altitude Platform (HAP) One of the newest ideas in satellite communication. A blimp or plane around 20 km above the earth’s surface is used as a satellite. HAPs would have very small coverage area, but would have a comparatively strong signal. Cheaper to put in position, but would require a lot of them in a network. 4/23/2017 Dr. Hassan Yousif

Kepler’s Work Tycho Brahe led a team which collected data on the position of the planets (1580-1600 with no telescopes). Mathematician Johannes Kepler was hired by Brahe to analyze the data. He took 20 years of data on position and relative distance. No calculus, no graph paper, no log tables. Both Ptolemy and Copernicus were wrong. He determined 3 laws of planetary motion (1600-1630).

Kepler’s First Law The orbit of a planet is an ellipse with the sun at one focus. A path connecting the two foci to the ellipse always has the same length.

Orbital Description An ellipse is described by two axes. Long – semimajor (a) Short – semiminor (b) The area is pab (becomes pr2 for a circle). b a

Orbital Speed The centripetal force is due to gravity. GMm/r2 = mv2/r v2 = GM/r Larger radius orbit means slower speed. Within an ellipse larger distance also gives slower speed.

Kepler’s Second Law The line joining a planet and the sun sweeps equal areas in equal time. Dt The planet moves slowly here. Dt The planet moves quickly here.

Orbital Period The speed is related to the period in a circular orbit. v2 = GM/r (2pr/T)2 = GM/r T2 = 4p2r3/GM Larger radius orbit means longer period. Within an ellipse, a larger semimajor axis also gives a longer period.

Kepler’s Third Law The square of a planet’s period is proportional to the cube of the length of the orbit’s semimajor axis. T2/a3 = constant The constant is the same for all objects orbiting the Sun direction of orbit semimajor axis: a The time for one orbit is one period: T

VSAT VSAT stands for Very Small Aperture Terminals. It allows for the provision of Broadband services using Satellite technology. This technology has been deployed for many years and was traditionally reserved for large telecommunication operators. Modern VSAT technology now allows small businesses and residential users to avail of the opportunity to receive Broadband services via satellite.

4/23/2017 Dr. Hassan Yousif

satellite based, ‘always-on’ Internet access. VSAT is a platform, which uses satellite terminals upon which broadband application services and electronic commerce activity have the potential to advance and develop. VSAT offers satellite based, ‘always-on’ Internet access. A VSAT network consists of three components: ■ A central hub ■ A satellite ■ A virtually unlimited number of VSAT user terminals. 4/23/2017 Dr. Hassan Yousif

Wireless local loop (WLL) What is WLL? - WLL is a system that connects subscribers to the local telephone station wirelessly. Systems WLL is based on: Cellular Satellite (specific and adjunct) Microcellular Other names Radio In The Loop (RITL) Fixed-Radio Access (FRA).

A general WLL setup

WLL services Desirable: Other: Wireless feature should be transparent Wireline Custom features Other: Business related Hunt groups, Call transfers Conference calling Calling cards, coin phones V.29 (9600bps) ISDN (64kbps)

Advantages of WLL over Wired Approach Cost – wireless systems are less expensive due to cost of cable installation that’s avoided Installation time – WLL systems can be installed in a small fraction of the time required for a new wired system Selective installation – radio units installed for subscribers who want service at a given time With a wired system, cable is laid out in anticipation of serving every subscriber in a given area

Propagation Considerations for WLL Most high-speed WLL schemes use millimeter wave frequencies (10 GHz to about 300 GHz) There are wide unused frequency bands available above 25 GHz At these high frequencies, wide channel bandwidths can be used, providing high data rates Small size transceivers and adaptive antenna arrays can be used

Thank you 4/23/2017 Dr. Hassan Yousif