ECE405 Satellite Communication

Dr. S. Hariharan
Associate Professor
Department of Communication Engineering
School of Electronics Engineering
VIT University
Vellore

Dr. S. Hariharan, SENSE, VIT. ECE405 - Satellite Communication 1

 Summary
&
Formulas
ECE405 Satellite Communication

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 2

 Introduction
Satellite system consists of
o Earth segment (traffic and control)
o Space segment

satellite orbits
o Low Earth Orbit (LEO)
o Medium Earth Orbit (MEO)
o Geosynchronous orbit (GSO)
o Geostationary orbit (GEO)

Two links
o Uplink – ground to satellite
o Downlink – satellite to ground

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 3

 Microwave frequency bands

L band: 1-2GHz
S band: 2-4GHz
C band: 4-8GHz
X band: 8-12GHz
Ku band: 12-18GHz
K band: 18-26.5GHz
Ka band: 26.5-40GHz
Majority of existing systems operate in C and Ku

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 4

 Common Frequency Bands and typical
applications

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 5

 Common Frequency Bands and typical
applications

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 6

 Service Types

o Fixed Service Satellites (FSS)

o Example: Point to Point Communication
o Broadcast Service Satellites (BSS)
o Example: Satellite Television/Radio
Also called Direct Broadcast Service (DBS).
o Mobile Service Satellites (MSS)
o Example: Satellite Phones

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 7

 Kepler’s laws
o Centrifugal force
o Centripetal Force
o Orbital Elements

• Semi-Major axis (a)-Size

• Eccentricity (e) – Shape

• Inclination (i).
• Right ascension of ascending node (Ω) . Orientation
• Argument of Perigee (ω)

• True anomaly (γ) - Location within orbit

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 8

 Kepler’s laws
First Law: Planets orbit the sun in ellipses with the sun at one focus.
Second Law: Each planet moves in so that an imaginary line drawn from the sun to
any planet sweeps out equal areas of space in equal intervals of time.
Third Law: The square of the orbital period (T ) of a planet is directly proportional
to the cube of the average distance of the planet from the sun (r )
p
r p
h2
1  e cos  
 4 2
 3
T 
2
a
  
𝜇
𝑣=
𝑟 G  6.672 10 11 Nm 2 /kg 2
M E  5.98 10 24 kg
  3.986 105 km 3 /s 2
Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 9
 ORBIT CHARACTERISTICS

p h2
a 𝑝 = 𝑎(1 − 𝑒2) or p
1  e2 
h is the magnitude of the angular momentum


b  a 1 e 
2 1/ 2
Where, e
h 2C


NOTE: For a circular orbit, a = b and e = 0

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 10

 ORBIT CHARACTERISTICS

2 1 ra  rp
Velocity at apogee
2
𝑉𝑎 = 𝜇 − a
𝑟𝑎 𝑎 2
2 1
Velocity at perigee 𝑉𝑝2 =𝜇 −
𝑟𝑝 𝑎

e is the eccentricity of the orbit

ab
e
ab

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 11

 The Geostationary Orbit
Sidereal Day = 23 hr. 56 min 4.09 sec.
Radius and height of GEO orbit:
T2 = (4 2 a3) / 
a3 = T2  /(4 2)
T = 86,164.1 sec
a3 = (86,164.1) 2 x 3.986004418 x 105 /(4 2)

a = 42,164.172 km = orbit radius

Orbit height (h) = orbit radius – earth radius
= 42,164.172 – 6378.14
= 35,786.03 km

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 12

 LOOK ANGLES
Geometry for Elevation Calculation

El =  - 90o
 = central angle
rs = radius to the satellite
re = radius of the earth

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 13

 LOOK ANGLES

SUB-SATELLITE POINT
Latitude Ls
Longitude ls
EARTH STATION LOCATION
LatitudeLe
Longitude le
Calculate , ANGLE AT EARTH CENTER
Between the line that connects the earth-center to the satellite and the line
from the earth-center to the earth station.

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 14

 LOOK ANGLES

 is defined so that it is non-negative and

cos () = cos(Le) cos(Ls) cos(ls – le) + sin(Le) sin(Ls)
1/ 2
 r  2
 re  
Range : d  rs 1     2  cos 
e

  rs   rs  

sin  
Elevation : cos (El )  1/ 2
 r  2
 re  
1     2  cos 
e

  rs   rs  

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 15

 LOOK ANGLES

GEOSTATIONARY SATELLITES
SUB-SATELLITE POINT
(Equatorial plane, Latitude Ls = 0o, Longitude ls)
EARTH STATION LOCATION
Latitude Le
Longitude le
GEO - simplified formulas

cos(γ) = cos(𝐿𝑒) cos(𝑙𝑠 – 𝑙𝑒)

Using rs = 42,164 km and re = 6,378.14 km gives
d = 42,164 [1.0228826 - 0.3025396 cos()]1/2 km
sin  
cosEl  
1.0228826  0.3025396 cos 1/ 2

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 16

 LOOK ANGLES
AZIMUTH CALCULATION – GEO
Intermediate angle is calculated as,

 tan ls  le  
  tan  1

 sin Le  
Case 1: Earth station in the Northern Hemisphere with
(a) Satellite to the SE of the earth station: 𝐴𝑧 = 180𝑜 − 
(b) Satellite to the SW of the earth station: 𝐴𝑧 = 180𝑜 + 

Case 2: Earth station in the Southern Hemisphere with

(c) Satellite to the NE of the earth station: 𝐴𝑧 = 
(d) Satellite to the NW of the earth station: 𝐴𝑧 = 360𝑜 − 

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 17

 VISIBILITY TEST
re
rs 
cos 
 re  1  6378 
  cos    cos 
1

 rs   42164 
For Geostationary Satellites   81.3o

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 18

 Locating the satellite

Orbit Determination
Algorithm summary:

1. Calculate average angular velocity:    1/ 2 / a 3 / 2

2. Calculate mean anomaly: M   t  t p  Time reference

3. Solver for eccentric anomaly: M  E  e sin E 

r0  a1  e cosE ;
4. Find polar coordinates:
0  cos 
 
 a 1  e 2  r0 
1

 er 
x0  r0 cos0 ;
0
5. Find rectangular coordinates
y0  r0 sin 0 

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 19

 Key Points

 Kepler’s laws of planetary / satellite motion

 Equation of satellite orbits
 Describing the orbit of a satellite
 Locating the satellite in the orbit

 Orbital perturbations
 Launching methods and launch vehicles
 Placing a satellite in a geo-stationary orbit - Orbit raising
 Orbital effects

 Satellite subsystems
 Communication subsystem
 Block diagrams of transponders

Dr. S. Hariharan, SENSE, VIT ECE405 - Satellite Communication 20