Satellite Network communication System

1. Satellite Network
commuNicatioN SyStem
BY
eNG .. mohamed ahmed
el SadaNy

2. Main points
 History of satellite system .
 Usage of satellite .
 Types of Satellite Orbits.
 Coverage area of satellites.
 Bands of frequency.
 Look Angles .
 Transmitter system .
 Satellite system .
 Receiver system .

3. History
 The Moon is the 1st passive reflector and in the late of 1940 to
1950 , became the1st satellite transponder .
 In 1954 , U.S Navy successfully transmitted the 1st message
over this earth-to-moon-to-earth relay .
 In 1957 , Russia launched the first active satellite (Sputnik1) , it
transmitted telemetry information for 21 days .
 Later in 1957 , US launched (Explorer 1) , it transmitted
telemetry information for nearly 5 months .
 In 1958 , NASA launched (Score) , it rebroadcasted President
Eisenhower’s Christmas message .
 In 1962 , American telephone and telegraph company (AT&T)
launched (Telstar 1) ,the first simultaneously satellite .

4. Usage

5. Types of Satellite Orbits
1. Based on the inclination , i, over the
equatorial plane.
› Equatorial Orbits above Earth’s equator (i=0°)
› Polar Orbits pass over both poles (i=90°)
› Other orbits called inclined orbits (0°<i<90°)
Equatorial Polar Inclined

6. Types of Satellite Orbits
2. Based on Eccentricity :
› Circular with centre at the earth’s centre.
› Elliptical with one foci at earth’s centre .

7. Types of Satellite Orbits
3. Based on the Satellite Altitude:
a- GEO-Geostationary Orbits
b- MEO – Medium Earth Orbits
c- LEO – Low Earth Orbits

8. Types of Satellite Orbits

9. Geo –Geostationary Orbit
 The most common type of communication satellite
today is Geostationary satellite(GEO).
 GEO satellites remain in the same position relative to
the surface of earth.
 If the satellite is in the circular orbit 35863 KM above
the surface of the Earth and rotates in the equatorial
plane of the earth and rotates at the exactly same
speed of earth then that satellite is referred as GEO
satellite.
 In GEO there is no problem with signal (freq) changes
due to relative motion of satellite and antennas on
the earth.

10. Geo –Geostationary Orbit
 Tracking of satellite by its earth station is very simplified and easy.
GEO satellites have a 24 hour view of a particular area.
 Three satellites in Geostationary orbit separated by the angle of 120
degrees can cover the entire earth except the areas near south &
north poles.
 A GEO satellite’s distance from earth gives it a large coverage area.
 The signal might be weak after travelling 35863 KM.
 Delay in the signal beneath and back of the satellite.
 The polar regions might poorly covered by the GEO satellites.

11. MEO – Medium Earth Orbits
 A MEO satellite is in orbit somewhere between 8,000 km
and 18,000 km above the earth’s surface.
 MEO satellites are similar to LEO satellites in functionality.
 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.

12. 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 LEO satellite’s proximity to earth compared to a GEO
satellite gives it a better signal strength and less of a time
delay, which makes it better for point to point
communication.
 A LEO satellite’s smaller area of coverage is less of a
waste of bandwidth.

13. Low Earth Orbit (LEO)
 Large constellation of satellites is needed for continuous
communication (66 satellites needed to cover earth).
 LEO satellites have to compensate for Doppler shifts
cause by their relative movement.
 Atmospheric changes effect the LEO satellites, causing
gradual orbital distortion

14. Coverage area of satellites
 Every satellite have a footprint or
coverage area , it is differenced
between each satellite and other .
 it means the area that this satellite
coverage it by it’s beam and in any
difference position we can’t transmit or
receive any signal to this satellite .

15. Coverage area
W2A :: 10° EAST

16. Frequency Bands
ISSUES up-LINK(GHz) DOWN-LINK
(GHz)
BAND
Interference with ground
links
6 (5.925-6.425) 4 (3.7-4.2) C
Attenuation due to rain 14 (13.7-14.5) 11 (10.7-12.7) Ku
High Equipment cost 30 (27.5-30.5) 20 (17.7-21.7) Ka

17. Look Angles
 To orient an earth station antenna
toward a satellite , it is necessary to know
the Elevation angle and Azimuth angle.

18. Angle of Elevation
 It is the angle formed between the plane
of a wave radiated from an earth station
antenna and the horizon .

20. Angle of Azimuth
 It is defined as the horizontal pointing
angle of an antenna , it is measured in
an clockwise direction in degrees from
true north .

21. Uplink Model
 It is the model of the transmitter system towards the satellite , it contains 4
steps :
– Encoding .
– Modulation .
– Up Converter .
– Power Amplification .
– Encoding is an operation to convert audio and video to a digital stream of 0’s and 1’s
.
– Modulation is an operation to modulate the signal in 4MHz frequency range with a
carrier signal in 70MHz frequency range by change in one only chs of the signal
(Frequency , Amplitude or Phase ) .
– Up converter is an operation to convert the frequency from the IF range to the SHF
range by multiplexing the freq, by Local oscillator freq
– Power Amplification is an operation to amplify the signal power to can reach to the
satellite .

22. PSK,QPSK,
QAM or
8PSK
Uplink Model
Modulator BPF
IF
X
LO (mw
generator)
BPF
Up converter
HPA
Free space
losses
Other
losses
Antenna
Satellite Transponder
receive section
RF
Enc, signal I/P

23. Satellite Transponder
 It is an RF to RF repeater A typical satellite transponder
consists of :
– Band Pass Filter (BPF) .
– Low Noise Amplifier (LNA).
– Frequency Translator .
– Low –Level Power Amplifier .
– BPF is an electronic device that can make limiting to the signal
and pass a determine band frequency.
– LNA is a tunnel diode .
– Freq, Translator is a shift oscillator and BPF which converts the
high band up link freq, to low band down link freq, .
– Low –Level Amplifier is a travelling wave tube that amplify the
RF signal for transmission through antenna to earth station .

24. Satellite Transponder
BPF
LNA
X
LO
Filter LPA
Frequency
translator
Mux
Towards
Earth Station
From Earth
Station

25. Downlink Model
 It is the model of the receiver system towards the earth
station , it contains 5 steps :
– Band pass filter(BPF).
– Low Noise Amplifier (LNA).
– Down Converter .
– Demodulator .
– Decoding .
– Down converter is an operation to convert the frequency from the
RF range to IF range by multiplex the freq, by Local oscillator
freq, .
– Demodulator is an operation to demodulate the signal in 70MHz
frequency range to the original signal in 4MHz frequency range .
– Decoding is an operation to have on the signal that was sent to sat,
in the original form audio and video .
–

26. Downlink Model
Satellite
transmitter
Free space
losses
Other
losses
X
LO
BPF LNA BPF Demod
IF
Down converter
Earth station
Antenna
Data
out
Decoding

27. Q & A

28. Thanks