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

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

3. 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

4. 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

5. Low Earth Orbit (LEO)
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Dr. Hassan Yousif

6. 4/23/2017
Dr. Hassan Yousif

7. 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.
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Dr. Hassan Yousif

8. LEO (cont.)
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Dr. Hassan Yousif

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

10. 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

11. 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

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

13. 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

14. Kepler’s Work
Tycho Brahe led a team which collected data on the position of the planets ( 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 ( ).

15. 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.

16. 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

17. 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.

18. 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.

19. 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.

20. 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

21. 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.

22. 4/23/2017
Dr. Hassan Yousif

23. 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

24. 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).

26. A general WLL setup

27. 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)

28. 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

29. 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

30. Thank you
4/23/2017
Dr. Hassan Yousif