EC 8094 SATELLITE COMMUNICATION - COURSE MATERIAL

KONGUNADU COLLEGE OF ENGINEERING AND TECHNOLOGY
(AUTONOMOUS)
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING
EC8094 SATELLITE COMMUNICATION (R-2017)

EC8094 SATELLITE COMMUNICATION
UNIT I - SATELLITE ORBITS
Kepler‟s Laws, Newton‟s law, orbital parameters, orbital perturbations, station
keeping, geo stationary and non Geo-stationary orbits – Look Angle
Determination- Limits of visibility –eclipse-Sub satellite point –Sun transit outage-
Launching Procedures – launch vehicles and propulsion.

INTRODUCTION
Orbit
•An orbit is a curved path, like a circle or oval (ellipse)
Satellite
•An object in orbit is called a satellite.
•In general, a satellite is anything that orbits something else.
Communications Satellite (SATCOM)
•A satellite is a specialized wireless receiver/transmitter that is launched by a rocket
and placed in an orbit around the earth.
Advantages:
•A satellite can link many users who are widely separated geographically, since very
large areas are visible from the satellite.

FREQUENCY ALLOCATIONS FOR SATELLITE SERVICES
• International Telecommunication Union (ITU).
Three regions:
The world is divided into three regions to reduce the difficulties in frequency planning.
• Region 1: Europe, Africa (formerly the Soviet Union) and Magnolia.
• Region 2: North and South America and Greenland
• Region 3: Asia (excluding region 1 areas), Australia and the South West Pacific.

DEFINITIONS OF TERMS FOR EARTH ORBITING
SATELLITES
Subsatellite path:
• This is the path traced out on the earth‟s surface directly below the satellite
Apogee (ha):
• The point farthest (at the greatest distance) from earth.
Perigee (hp):
• The point closest approach to earth.
Line of apsides (la):
• The line joining the perigee and apogee through the center of the earth.
Ascending node:
• The point where the orbit crosses the equatorial plane going from south to north.
Descending node:
• The point where the orbit crosses the equatorial plane going from north to south.

COND…
Line of nodes:
•The line joining the ascending and descending nodes through the center of the earth.
Inclination (i):
•The angle between the orbital plane and the earth‟s equatorial plane.
Prograde Orbit:
•An orbit in which the satellite moves in the same direction as the earth‟s rotation.
•The inclination of a prograde orbit lies between 0 Degree and 90Degree.
Retrograde orbit:
•An orbit in which the satellite moves in a direction opposite (counter) to the earth‟s
rotation
•The inclination of a prograde orbit lies between 90 Degree and 180Degree.

COND…
Argument of Perigee ():
•The angle from ascending node to perigee.
Right ascension of the ascending node():
•This is the angle measured eastward in the equatorial plane from the line of Aries ()
to the ascending node.
•The line of Aries () is an imaginary line drawn from the equatorial crossing to the
first point of Aries through the center of the sun points.
Mean Anomaly (M):
•Mean anomaly „M‟ gives an average value of the angular position of the satellite with
reference to the perigee.
True anomaly:
•True anomaly is the angle from perigee to the satellite position, measured at the
earth‟s center.

KEPLER‟S LAWS
• The fundamental properties of orbits are summarized in Johannes Kepler‟s three
laws of planetary motion.
The three laws are:
• Kepler‟s First Law
• Kepler‟s Second Law
• Kepler‟s Third Law
1)Kepler‟s First Law:
“ the path followed by a satellite around the primary will be an ellipse”
• An ellipse with focal points F1 and F2,semimajor axis a and semiminor axis b The
eccentricity of the ellipse is given by

Where, a – semimajor axis of the ellipse
b – semiminor axis of the ellipse
Conditions:
❖ When 0 < e < 1 , the orbit is elliptical
❖ When e = 0, the orbit becomes circular

Kepler‟s Second Law
“for equal time intervals, a satellite will sweep out equal areas in its orbital
plane which is focused at the barycenter”
• Now, the two areas A1 and A2 will be equal.
• The average velocity in each case = S1 and S2 m/s
• According to equal area law, velocity S2 < velocity S1..

Kepler‟s Third Law
“ The square of the periodic time of orbit is proportional to the cube of the
mean distance between the two bodies.”
This can be expressed as;
•Where, mean distance = semimajor axis „a‟
•n – periodic time of orbit (mean motion of the satellite) in radians/second
• - earth‟s geocentric gravitational constant
• = 3.986005 x 1014 m3/s2

NEWTON‟S LAWS
Sir Isaac Newton developed two laws of orbital mechanics from which kepler‟s laws
can be derived.
❖ Newton‟s law of universal gravitation
❖Newton‟s second law of motion
❖1) Newton‟s Law of Gravitation
•“the gravitational force of attraction between two bodies (with mass „M‟ and „m‟) is
directly proportional to the product of their masses and inversely proportional to the
square of the distance „r‟ between them”.

Newton‟s Second Law of Motion
• “the acceleration of a body is directly proportional to the force acting on it and is
inversely proportional to its mass”
• where a – acceleration
• F – Force
• m – Mass of the body

STATION KEEPING (or) ORBIT CONTROL
• The geostationary satellite should be kept in its correct orbital slot. Therefore, in
addition to controlling the attitude, orbital position should also be controlled. This is
known as station keeping.
Reason:
• The reason for the slow drift of satellite from the orbit is the equatorial ellipticity of
the earth.
Types:
Two types of operations being done for station keeping are
• 1. East-West station-keeping maneuvers
• 2. North-South station-keeping maneuvers

East-West Station-Keeping Maneuvers
•Here, the drift is opposed by an oppositely directed velocity component which is given
to the satellites by using jets. These jets are operated once every 2 or 3 weeks.
•As a result, the satellite will remain in its original position until the jets are operated
once again.
•These maneuvers are termed east-west station-keeping maneuvers. This is mainly done
for drift in longitude.
❖ Longitude tolerance limit for C band :  0.10
❖ Longitude tolerance limit for Ku band :  0.050

North-South (Latitude) Station-Keeping Maneuvers
• The geostationary satellite may move from its position in latitude also. The main
reason for this is the gravitational pull of the sun and moon.
• The rate of change of inclination due to this will be 0.85Degree/year.
• If this is not corrected, the inclination would change from 0Degree to 14.67Degree
in 26.6 years.
• To prevent this shift in inclination, some jets are used. These jets are operated at
correct times to make the inclination zero as well as to halt

THE GEOSTATIONARY ORBIT (GEO)
•Geostationary orbit is an orbit in which a satellite appears to be stationary with respect
to the earth.
•There is only one geostationary orbit
•center of the orbit must coincide with the center of the earth.
Conditions Required:
(i) The satellite must travel eastward at the same rotational speed as the earth, which is
constant.
(ii) The orbit must be circular.
(iii) The inclination of the orbit must be zero

•Geostationary Height
Geostationary height is the distance between the earth and geostationary orbit. It can be
found by the expression.
To find the radius of the orbit:
For a circular orbit, the semimajor axis is equal to the radius. Hence, by using Kepler‟s
third law, the radius can be given as,
Where,  - Earth‟s geocentric gravitational constant = 3.986005 x 1014 m3/s2
•P – period for the geostationary: the time taken for the earth to complete one rotation
with respect to its N-S axis
•P = 23h, 56 min 4s

Substituting these value in equ. (1.20) the orbit radius is
aGSO = 42, 164 km
Now, the geostationary height from eqn. (1.19) is
Types:
All the non-geostationary orbits can be grouped into the following categories.
❖ Low Earth Orbits (LEO)
❖ Polar Orbits
❖ Medium Earth Orbits (MEO)

Low Earth Orbits (LEO):
The height of LEO should be high enough to avoid atmospheric drag. It ranges from
750 to 1500 km.
Service provided:
❖ Two way message services
❖ Data communications services
❖Position determination.
Examples: ORBCOMM:
Orbcomm stands for the Orbital Communications Corporation System. This is a
low earth orbiting satellite system.
❖ It is designed for worldwide data messaging and position determination.
❖ This system has 20 to 24 satellites in circular orbits.
❖ The altitude of the orbits is 970 km.

Polar Orbits:
Polar orbits are a special case of LEOs. These are almost circular orbits and the
satellites in these orbits could cover the north and south polar regions.
Orbit Altitudes and Inclination:
•Polar orbits are at a height between 800 and 900 km above earth. They have an
inclination of 90Degree.
Services provided:
•The polar orbiters which are also known as LEOSATS provide the following services.
(1)Environmental monitoring
(2) Search and rescue service
(3) Provide a wide range of data.
(4) Carry ultraviolet sensors to measure ozone level.
Example – IRDIUM:
❖ IRIDIUM is a LEO satellite constellation that consists of 77 satellites.
❖ These satellites are in polar orbits at an altitude of 765 km.
❖ They are in 7 orbital planes with 11 satellites in each plane

Medium Earth Orbit (MEO):
•Medium earth orbits are also almost circular orbits.
Orbit altitude:
The height of MEOs extends from 10,000 km to 20,000 km above the earth.
Service provided:
Following are some important applications for which MEOSATS are used.
❖ Mobile satellite service (MSS)
❖ Navigation
❖Precision location determination
Example – GPS:
❖ GPS stands for Global Positioning System.
❖ It is a constellation of 24 satellites in 12-h circular orbits.
❖ The altitude of orbits is 20,182 km and they are inclined at 55Degree.
❖ These satellites are in 6 orbital planes with 4 satellites in each plane. Therefore,
atleast 4 satellites are visible from any point on earth at all times.
❖ This system is developed for navigation, precision location determination and
time transfer between standards laboratories.

ORBITAL PERTURBATIONS
•The ideal keplerian orbit assumes the earth as a uniform spherical mass.
•It also assume that the only force acting is the centrifugal force which results from the
satellite motion for balancing the gravitational pull of the earth.
•But in actual practice, there are so many perturbing forces i.e. disturbing forces for an
orbit. The main forces are:
➢ Effects of a Nonspherical Earth
➢ Atmospheric Drag

Effects Of A Nonspherical Earth:
• According to Kepler‟s third law, the nominal mean motion n0 of a spherical earth
of uniform mass is given by,
Oblate Spheroid:
The earth is not perfectly spherical, it has a bulge at the equator and a flattening
at the poles. This shape is known as oblate spheroid.
• When this is taken into account, the mean motion is modified to,

Anomalistic Period:
•The orbital period of the earth when considering its oblateness is termed the
anomalistic period.
•Where, n →mean motion in rad/s
Effects of Oblateness:
•Two changes in the orbital plane are produced by the nonspherical earth.
They are;
i. Regression of the nodes
ii. Rotation of the line of apsides.

i. Regression of the nodes
Three things happen here are:
❖ The nodes appear to slide along the equator
➢ If the orbit is prograde, the nodes slide westward and if retrograde, they slide
eastward.
❖ Because of this, the line of nodes in the equatorial plane rotates about the center of
the earth
❖ Thus, the right ascension of the ascending node () shifts its position.

ii. Rotation of the line of apsides
• This is the other major effect produced by the equatorial bulge.
• Due to this rotation, the argument of perigee (ꙍ ) changes with time.
• The rate of change is given by,
Overall Effect:
• Thus the satellite drifts as a result of the regression of the nodes and the latitude of
perigee changes as a result of the rotation of the line of apsides.

Atmospheric Drag
• The effects of atmospheric drag are considerable only for near-earth satellites (ie)
the satellites which are below 1000 km from the earth.
• Effects:
• The drag is greatest at the perigee and it reduces the velocity at this point.
• The semimajor axis and the eccentricity are reduced because of this drag.

LIMITS OF VISIBILITY
• There will be east and west limits on the geostationary arc which are visible from
any given earth station. These are known as Limits of Visibility.
• Longitudinal Limits Calculation:
• Longitudinal limits can be calculated by considering an earth station at the equator,
with the antenna pointing either west or east along the horizontal as shown in fig.

Limiting angle:
From Fig:
Longitudinal Limits

Limits of Latitude Calculation
•The limits of visibility also depends on the earth station latitude. As shown in fig;
•Where,
•El min → minimum value of elevation. This is used to avoid reception of excessive
noise from the earth, typical value is 5Degree.
•Applying sine rule, the angle subtended at the satellite S is found to be,

ECLIPSE
•Eclipse is defined as the cutting off the light of the sun, totally or partially.
Earth Eclipse of Satellites:
•Geostationary satellites are eclipsed by the earth
•This happens when the earth‟s equatorial plane coincide with the plane of the earth‟s
orbit around the sun.
•The plane of the earth‟s orbit around the sun is known as the „ecliptic plane‟.
•ecliptic → the orbit of the sun

Spring and Autumn Equinoxes
Equinox → time when day and night are of equal length;
spring → season between winter & summer;
Autumn → season between summer & winter
•Since the equatorial plane is tilted at an angle of 23.40 to the ecliptic plane, the
satellite will be in full view of the sun for most days of the year as in position A

Periods of eclipse:
• When the sun crosses the equator around the spring and autumnal equinoxes, the
satellite will pass into the shadow of the earth at certain periods.
Eclipse and Equinox:
• Eclipses begin 23 days before equinox and end 23 days after equinox.
• Minimum duration of the eclipse is 10 min and maximum duration is about 72
min.

Effects of Eclipse:
• When a communications satellite is in the shadow of the earth, it will not get solar
radiation and this creates two important effects. They are,
a) There is no primary power supply for the satellite
b) There is sudden and sharp change in the temperature balance of satellite.

THE SUBSATELLITE POINT
•The subsatellite point is the point on the earth which is vertically under the satellite.
•If the radius vector r is known, we can determine.
❖ latitude and longitude of the subsatellite point
❖height of the satellite above the subsatellite point.

SUN TRANSIT OUTAGE
• Transit of the satellite between earth and sun.
• It is another event which happens during equinoxes.
• When this happens, the sun appear as an extremely noisy source and it completely
blanks out the signal from the satellite.
• Maximum outage time is 10 min.

LAUNCHING PROCEDURES
• If the orbit into which a satellite has to be placed is of low altitude.
• i.e. upto 200km, the satellite may be directly injected into the orbit from a launch
vehicle.
• But, for higher altitudes, it is not economical. and requires more power.
• In such cases, before reaching the final orbit, satellites should orbit in two
intermediate orbits, known as
• ❖ Parking orbit and
• ❖ Transfer orbit

Parking Orbit
• These parking orbits are Low Earth Orbits (LEOs) which are nearly circular and are
at altitudes between 150 and 300 km.
Hohmann Transfer Orbit:
• Next, the launch vehicle inserts the satellite into a transfer orbit. Such an orbit is
known as a „Hohmann Transfer Orbit‟.

Transfer between two Circular Orbits
•Here, the Hohmann elliptical orbit is tangent to
❖ the low-altitude orbit at perigee and
❖the high altitude orbit at apogee

LAUNCH VEHICLES
•The launching of a satellite into an orbit is a very complex and expensive operation.
•In most cases, the launch vehicle‟s cost is same as the satellite itself.
•A launch vehicle can be considered as a system that includes the following
❖ Structure
❖ Engines
❖ Propellant storage and pumps
❖ Guidance and
❖ Control

Types
Launch vehicles can be classified into two as
(i) Expendable
(ii) Reusable
• Reusable launch vehicle or „space shuttle‟ was developed to replace the expendable
launch vehicles, which is also known as „Space Transportation System‟ (STS).

Expendable Vehicle Launch - Example
i) Solar – Sail Type Satellite
• One example of expendable launch vehicle is INTELSAT V
• Starting from the launch to its station acquisition, it has 21 stages

The stages and the time taken for each stage are:
1. Atlas Centaur launch : T0
2. Jettison fairing :T0 + 215s
3. Transfer orbit injection : T1 = T0 +
27m
4. Centaur reorientation to orbit normal :
T1 + 10s
5. Satellite separation : T1 + 2m
6. Spin up : T1 + 2m + 2s
7. TC & R line established : T1 + 20m
8. Orbit and attitude determination : T1 +
30m
9. Reorientation to apogee motor fire
attitude : T2 + 2.8h
10. Final attitude adjustment : T2 - 2.4h
11. Apogee motor firing : T2
12. TC & R antenna coverage
reorientation
13. Orbit and attitude determination : T2
+ 1 20h
14. Reorientation for drift orbit velocity
correction : T2 + 20h
15. Initiate drift orbit velocity correction :
T2 + 23.75h
16. Drift orbit velocity correction
complete : T3 =T2 + 24.25h
17. Design : T3 + 5m
18. Deploy solar arrays and antennas : T3
+ 15m
19. Sun acquisition : T3 + 1h
20. Earth capture : T3 + 4.5h
21. Station acquisition : T3 + 1 ฀ 2
months

Cylindrical Type Satellite
• Another one example of expendable launch vehicle is STS-7 / Anik C2 satellite.

Launch Vehicles for Commercial Satellites
1)Ariane
•The Ariane family of spacecraft launch vehicles are developed by European space
Agency (ESA) together with the French space agency (CNES).
•Ariane 1 - capability of 1850kg into geostationary transfer orbit
•Ariane 2, 3, and 4 were developed with different capabilities
•Ariane 5 - capability of 5900 kg into geostationary transfer orbit
2) Atlas – Centaur
❖ The Atlas launch system is the product of the General Dynamics Space Systems
Division of U.S.
❖ 1962 and then developed Atlas I, Atlas II, Atlas IIA and Atlas IIAS.

Cond…
3) Delta
❖ Delta launch vehicles are now managed by McDonnell Douglas for NASA, the
U.S Air force.
❖Delta II launches are capable of inserting a 1270 kg payload into GTO.
4) Titan
❖The first version of these launch vehicles, Titan I became operational in 1956.
❖Then Titan II was designed for NASA
❖Titan III for the U.S. Air force.
❖capability ofputting 14,000 kg into LEO
❖upto 5000 kg for direct insertion into GTO.

Cond…
5) H-I and I-II
❖H-I and H-II are launch vehicles of the National Space Development Agency of
Japan.
•Using these launchers, a variety of missions is possible, including lunar and plantary
probes(it’s a robotic spacecraft that doesn't orbit around the Earth)
6) Long March
❖This launcher was developed by China.
❖The long March 2E is the recently produced most powerful launcher
❖It has a payload capability of 93,000 kg into LEO
❖and 3370 kg into GTO.

PROPULSION
A propulsion subsystem is required for a communications satellite to
(1) maintain a proper orientation and spin rate in transfer orbit
(2) inject the satellite into geostationary orbit
(3) maintain the satellite at the correct longitude in the equatorial plane by station
keeping.
(4) help in attitude control.

KONGUNADU COLLEGE OF ENGINEERING AND TECHNOLOGY
(AUTONOMOUS)
DEPARTMENT OF ELECTRONICS AND COMMUNICATION ENGINEERING

UNIT II - SPACE SEGMENT & SATELLITE
LINK DESIGN
Spacecraft Technology- Structure, Primary power, Attitude and Orbit control,
Thermal control and Propulsion, communication Payload and supporting
subsystems, Telemetry, Tracking and command-Transponder- Antenna
Subsystems– launch vehicles and propulsion.

SPACE SEGMENT & SATELLITE
LINK DESIGN
Introduction:
The two broad divisions of a satellite communications system are
❖ Earth segment (or) ground segment.
❖Space segment.
•The space segment includes the satellites as well as the Telemetry, Tracking and
command (TT&C) facilities.
•The equipment's carried with the satellites are classified according to their function.
❖Payload
❖Transponder
❖Bus

SPACECRAFT TECHNOLOGY
•A spacecraft is a vehicle or machine designed to fly in outer space.
•The design of the spacecraft is a very complicated
•There are many problems and challenges to be faced starting from the launching of
satellite into the desired orbit.
STRUCTURE:
•It must be designed to withstand a variety of loads that include all the equipment's
aboard the satellite.
Parameters affecting the Structure
spacecraft should be capable of withstanding a number of parameters.
➢ Accelerations
➢ Aerodynamic loads and vibrations
➢ Centrifugal stresses
➢ Thermal stresses
➢ Separation shocks
➢ Radiation.

Typical Structural Types
Different design approaches use different spacecraft structures
(i) Longeron
(ii) Truss
(iii) Thrust tube

Materials Used
A variety of materials are used by different spacecraft techniques.
(1) Aluminium (5) Titanium
(2) Magnesium (6) Graphite-Reinforced Phenolic (GFRP)
(3) Stainless steel (7) Fiber-glass epoxy
(4) Invar (8) Beryllium

Example Structure
Typical structural arrangement of Anik-E spacecraft is shown in fig.

PRIMARY POWER
To provide primary power supply for a satellite, there are two possible sources today.
They are
❖ Nuclear supplies and
❖Solar supplies
Nuclear Primary Power Systems
•Where the solar energy is weak, such as for deep-space missions, nuclear supplies are
used.
Type 1: (Nuclear Reactor Type)
In this type, there is a boiler with a working fluid such as mercury. This boiler is heated
by a small nuclear reactor and vapor is produced. The vapor is used to drive a turbine -
alternator .
Type 2: (Thermoelectric Generator Type)
❖This is a commonly used type for smaller power supplies.
❖It has a single radioisotope thermoelectric generator(RTG)

Solar Primary Power Systems
Solar cells:
•Solar cells produce power, but individual cells can generate only small amounts of
power.
•Therefore, large number of solar cells should be arranged in series-parallel connection
called the ‘solar panels’.
Cylindrical Satellites:
Cylindrical type satellites have two panels, namely
➢ Outer panel
➢Telescoped panel.
•Solar cells are arranged around these panels or drums.
•During launch, only the outer panel is exposed to sunlight.
•after reaching the final orbit, both the panels generate electrical power.

Solar-Sail Type Satellites:
•In this type of satellites, to achieve high power, solar panels are arranged in a form
known as ‘rectangular solar sails’.
•These solar sails are folded during launch phase of the satellite and after reaching the
final orbit, they are extended and fully exposed to sunlight.
Service during Satellite Eclipse:
•A geostationary satellite is eclipsed by the earth twice a year during spring and
autumnal equinoxes. The maximum duration of an eclipse is 72 minutes. Therefore, to
operate the satellites during eclipse, storage batteries must be provided.
Examples of such storage batteries in use are
➢ Nickel- Cadmium (Ni-Cd) batteries
➢ Nickel-hydrogen (Ni-H2)batteries

Total Power Requirement:
(1) all Transmitters power
(2) receiver power
(3) housekeeping power and
(4) battery service during eclipse
(1) Total transmitter Power, Pt

(2)Total Transponder Power, PT:
To find this, the receiver power, Pr is added with the total transmitter power.
PT = Pt + Pr
(3) Housekeeping Power, Ph:
•The housekeeping power includes the power for the telemetry, tracking and command
(TT & C) subsystem, altitude control and propulsion.
Ph = Pho + Phe + hPT
Where,
•Pho – constant
•hPT - proportional to total transponder power, PT.
•Phe - eclipse heater power.
(4) Battery Power, Pe

Total Primary Power, P:
• Including all the estimated powers, the total primary power that must be provided
by the solar array is,
P = k (PT + Ph + Pc)
P = k [a(1+h) Pt + Pho + Pc]
Where, k – design margin factor

ATTITUDE CONTROL
•Needs
The attitude control subsystem should accomplish the following
❖ ensure that the directional antennas point in the proper direction
❖ make the earth-sensing instruments to cover the required regions
❖keep the solar arrays pointed toward the sun.
Disturbance Torques:
Disturbance torques are the forces which can alter the attitude.
(i) External forces:
❖ Gravitational fields of the earth and the moon.
❖ Solar radiation and
❖ Meteorite impacts.
(ii) Internal forces:
❖ Motor – bearing friction
❖ Movement of satellite elements such as antennas.

Horizon Detectors:
➢ Measure of satellite’s orientation in space.
➢Measure of satellite’s tendency to shift, if any
•Horizon detectors are infrared sensors which are used to detect border or edge of the
earth in space.
•By taking the centre of the earth as the reference point, four such sensors are used, one
for each quadrant of the earth.
•Therefore, if there is any shift in the orientation, of a satellite it will be detected by any
one of the sensor.
RPY (Roll, Pitch and Yaw) axes:

Basic Attitude –Control System:
Attitude Control Methods

i) Passive Attitude Control:
This method uses some mechanisms to stabilize the satellite without using energy
supply. An overall stabilizing torque will be applied.
Example:
• Spin Stabilization
• Gravity gradient stabilization
ii) Active Attitude Control
In this method, corrective torques are applied against the disturbance torques and there
is no overall stabilizing torque.
Example
• Momentum wheels method
• Electromagnetic coils method
• Mass expulsion devices method.

Spinning Satellite Stabilization

Momentum Wheel Stabilization
One wheel stabilization

Two wheel stabilization system

THERMAL CONTROL
•It is necessary that the mean spacecraft temperature and the temperature of all the
subsystems should be maintained within the limits suitable for satisfactory operation.
•Moreover, some devices such as valves, thrusters, bearings and deployment
mechanisms may fail to operate completely if the temperature is too high or too low.
Sources of Temperature:
❖ Radiation from the sun
❖ Radiation from the earth
❖ Radiation from the earth’s ‘albedo’
albedo → fraction of the radiation falling on earth and get reflected
❖ Heat generated by the equipment's in satellite itself.

Passive Techniques
•Within the spacecraft, thermal balance can be achieved by using simple passive
techniques.
•Some of such techniques are appropriate choices of materials, surface finish,
insulation and heat conductors.
1.Optical solar reflectors (OSRs) are used on
north and south panels.
2. Antenna is made from graphite expoxy to
minimize distortion.
3. Multilayer insulation is made on rare side of
antenna reflector and tower to minimize thermal
gradients.
4. Rear surface of solar panels is painted black for
high emittance.
5. East and west panels of spacecraft are covered with
multilayer insulation.

Active Methods
1.Thermal blankets and shields are used to provide insulation
2. Radiation mirrors are used to remove heat from the communications payload.
3. In Hughes HS376 satellite a mirrored thermal radiator is used. This radiator
provides path for the generated heat to escape into the surrounding space.
4.When the transponders are switched OFF, there will be heat reduction in satellites. To
compensate this, heaters may be switched ON at that times by giving command from
ground.

PROPULSION
Needs:
A propulsion subsystem is required for a communications satellite to
(1) maintain a proper orientation and spin rate in transfer orbit
(2) inject the satellite into geostationary orbit
(3) maintain the satellite at the correct longitude in the equatorial plane by
station keeping.
(4) help in attitude control.
Propellant
• The propellant used for propulsion can be Liquid or Gas.

Specific impulse:
• The characteristic that is used to describe the propellant performance is called
specific impulse, Isp. It is defined as

Reaction – control subsystem (RCS):
•A liquid propellant is used for transfer and drift orbit maneuvers, station keeping and
attitude control.
•This liquid propellant subsystem is known as the reaction-control subsystem.
•Example propellant: Hydrozine.
Early Propulsion Systems:
Early propulsion systems used ‘cold gases’ as propellants. Some example are
➢ Nitrogen
➢ Hydrogen peroxide
These systems had very low specific impulses when compared with liquid propellant
systems.
Types:
Two types of propulsion systems are
(1) Monopropellant systems
(2) Bipropellant systems

Monopropellant Systems:
•These are liquid propulsion systems that use hydrazine as the propellant.
Hydrazine (N2H4) Reactions:
•liquid with a boiling point of 114 Degree Celcius
•freezing point of 2 Degree Celcius
•The specific impulse of this systems is 220s.

Bipropellant Systems:
•These are also liquid propulsion systems, but their performance is higher than
monopropellant systems.
•Such systems are especially used for large spacecraft.
•Fuel ----→ Monomethyl hydrazine
•They have high specific impulse in the range of 290s to 310s.
•They have restart capability.
•Errors are corrected with less expense of fuel.

COMMUNICATIONS PAYLOAD & SUPPORTING SUBSYSTEMS
Communications Payload:
• the payload refers to the equipment or the scientific instrument carried by the
satellites to perform the function for which the satellite has been launched.
Supporting Subsystems:
• The supporting subsystems are carried along with the communications payload by
the vehicle or bus.
• The supporting subsystems are
(1) Structure
(2) Primary Power
(3) Attitude Control
(4) Thermal Control
(5) Telemetry, Tracking and Command
(6) Propulsion
(7) Transponders and Antennas

(1) Structure:
The structure supports the spacecraft during launch and in the orbital environment.
(2) Primary Power Subsystem:
It supplies electrical power to all the devices and equipments in the spacecraft.
(3) Attitude Control Subsystem:
This keeps the antennas pointed at correct earth locations and solar cells pointed at the
sun.
(4) Thermal Control Subsystem:
It maintains suitable temperature ranges for all subsystems during life, operating and
non-operating and in and out of eclipse periods.
(5) Telemetry, Tracking and Command (TT&C) Subsystem:
This system monitors spacecraft status, orbital parameters and controls the spacecraft
operation.
(6) Propulsion Subsystem:
The purpose are to maintain orbital position, major attitude control corrections, orbital
changes and initial orbit deployment.
(7) Communications Transponders and Antennas:
They receive, amplify, process and retransmit signals, and also they capture and radiate
signals.

TELEMETRY, TRACKING AND COMMAND (TT & C)
TT & C stands for Telemetry, Tracking & Command. Several routine communications
functions are performed by TT & C subsystem in the spacecraft.

Telemetry :
• Telemetering function can be known as measurement at a distance
• The satellite condition must be known on the ground at all times. Here, some
hundreds of points around the spacecraft are selected and quantities such as
voltages, currents, temperatures, pressures and the status of switches and solenoids
are measured.
Telemetry Data:
i. Attitude information
ii. Environmental information
iii. Spacecraft information – Eg: temperatures, power supply voltages and stored
fuel pressure.

Telemetry and Command:
•Telemetry subsystem transmits information about the satellite to the earth station.
•Command subsystem receives the command signals from earth station.
•Then it demodulates and decodes the signals.
•telemetry and command are complementary functions.
Functions:
The important functions performed by this telemetry and command are,
❖ Attitude changes
❖ Switching ON and OFF the communication transponders
❖ Antennas redirection
❖Enabling station-keeping maneuvers
Encryption of commands:
•Encrypt means ‘to hide’ (from the Greek word ‘kryptein’). To avoid reception of
unauthorized commands, the signals are encrypted. This is different from encoding
process.

Tracking:
• Tracking is very important. Because, various disturbing forces may change the
position of a geostationary satellite. Therefore, satellite’s movement is tracked and
correction signals are being applied.
• This is done by sending beacon signals ie guide signals from the satellite to the TT
& C earth stations.

UNIT III – SATELLITE LINK DESIGN
Basic link analysis, Interference analysis, Rain induced attenuation and
interference, Ionospheric characteristics, Link Design with and without frequency
reuse.

Basic link analysis
Satellite uplink and downlink Analysis and Design: Introduction:
•This chapter describes how the link-power budget calculations are made. These
calculations basically relate two quantities, the transmit power and the receive power,
and show in detail how the difference between these two powers is accounted for.
EQUIVALENT ISOTROPIC RADIATED POWER (EIRP):
It can be defined as the average power radiated from the antenna multiplied by the
gain of the antenna.
EIRP = GPs
Ps → Power radiated
G → Gain of the antenna

TRANSMISSION LOSSES
• The power input for transmission is the EIRP in dBW. Losses may occur along the
way of transmission.
• Therefore, to determine these losses, the power received at the other end should be
found.
Types of Losses:
There are various types of losses. The losses may be,
• constant
• estimated from statistical data
• dependent on weather conditions, especially on rainfall.
Some of these important losses we shall see in detail in the following sections are:
• Free-space transmission losses
• Feeder losses
• Antenna Misalignment losses
• Fixed atmospheric and Ionospheric losses.

FREE-SPACE TRANSMISSION[FSL]:
•Free-space transmission loss is the power loss resulting from the spreading of the
signal in space.
FEEDER LOSSES:
•Feeder losses are the power losses occur in the connection between receive antenna
and the receiver proper.
•These losses may occur in the connecting waveguides, filters and couplers.
[PR] = [EIRP] + [GR] – {[FSL] + [RFL]}
ANTENNA MISALIGNMENT LOSSES [AML] (Off Axis Losses):

THE LINK POWER BUDGET EQUATION:
The link power budget equation is the equation to find out the received power.
The decibel equation for received power is
•[PR] = [EIRP] – [LOSSES] + [GR]
•Where, PR → Received Power, dBW
•EIRP → Equivalent Isotropic Radiated Power, Dbw
•GR → receiver antenna gain
To identify the [LOSSES] , all type of losses should be taken into account.
•[LOSSES] = [FSL] + [RFL] + [AML] + [AA] + [PL]
•Where, FSL→ Free Space reading Loss, dB
•RFL→ Receiver Feeder Loss, dB
•AML→ Antenna Misalignment Loss, dB
•AA → Atmospheric Absorption loss, dB
•PL→ Polarization Mismatch Loss, dB

AMPLIFIER NOISE TEMPERATURE
• Consider the low noise amplifier (LNA) shown in fig, The available power gain of
the amplifier is given as G and the noise power output as Pno.
Input Noise from Antenna:
The input noise energy coming from the antenna can be written as,

Output Noise:
The output noise energy is No,out and it can be obtained as,
No,out =Gk (Tant + Te )
Te → equivalent input noise temperature of the amplifier
Total Noise to the Input:
•The total noise referred to the input of the amplifier is denoted as No, in. This is given
by
No,in = k (Tant + Te )
AMPLIFIERS IN CASCADE:
G = G1  G2

UPLINK
The uplink of a satellite circuit is the one in which the earth station is transmitting the
signal and the satellite is receiving it.
In otherwords, uplink is a transmission channel which carries signal from a station on
earth to a communications satellite.
CNR for Uplink:
The carrier to noise ratio for the uplink can be written from eqn.
•Where,
•EIRP → earth station EIRP
•G/T → satellite receiver G/T
•LOSSES → satellite receiver feeder losses, free space loss and other losses
•which are frequency dependent.
The three important considerations in the design of uplink which are explained in the
following sections are,
•Saturation flux density
• Input backoff
•The earth station HPA

DOWNLINK
The downlink of a satellite circuit is the one in which the satellite is transmitting the
signal and the earth station is receiving it.
In otherwords, downlink is a transmission path for the communication of signals and
data from a communications satellite to the earth.

EFFECTS OF RAIN
• Rainfall causes attenuation of radio waves by scattering and by absorption of
energy from the wave.
• Signal fading which affects the signal strength is caused mainly by rainfall.
Rain Attenuation:
• Rain attenuation increases with increasing frequency.
• It is worse in the Ku band than C band.
• Also, rain attenuation is accompanied by noise generation and both the attenuation
and the noise affect the satellite circuit performance badly.

Rain Attenuation Data:
• From the table, for example, at London, on average throughout the year, the rain
attenuation exceeds 0.3 dB for 1% of the time i.e. for 99% of the time attenuation is
equal to or less than 0.3 dB;
• Rain Depolarization:
• When raindrops fall through the atmosphere, they get flattened in shape and
become elliptical.
• If the wave has some arbitrary polarization, it becomes elliptically polarized due to
depolarization.
• Depolarizing devices can be installed to compensate for rain depolarization in
places where frequency reuse is achieved

Effects on Radome:
Some earth station antennas are operated under cover of a radome.
•Rain falling on a hemispherical radome forms a water layer of constant thickness.
•This layer introduces losses by absorption and reflection.
•Results show that a 1-mm thick layer introduces an attenuation of 14 dB.
•Therefore, earth station antennas should be operated without radomes wherever
possible.
Signal fading caused by rainfall places two limits which are:
 uplink rain fade margin
Downlink rain fade margin
UPLINK RAIN-FADE MARGIN:
As explained in the previous section rainfall attenuates the signal and increases the
noise temperature. This degrades the carrier to noise density ratio [C/N0] at the satellite
in two ways:
• By increasing the noise
• By affecting power output

DOWNLINK RAIN FADE MARGIN:
The Rainfall introduces attenuation by absorption and scattering of signal energy.
• Therefore, the received carrier – to – noise density ratio [C/N0] is degraded by the
rainfall in 2 ways.
• By attenuating the carrier wave
• By increasing the sky noise temperature

INTRODUCTION - Multiple Access
•The satellite operation can be divided into two access modes.
➢ Single access mode
➢Multiple access mode
Single Access Mode
❖ If a satellite is able to carry only one signal at a time, it is known as single
•access.
❖ In single access, the satellite is fully loaded by a single transmission from an earth
station. It means that, the whole available bandwidth of a transponder is occupied by a
single modulated carrier.
❖ Single access operation is used on heavy-traffic routes.
❖ This access requires large earth station antennas.

Multiple Access Mode
•The ability of the satellite to carry many, signals at the same time is known as multiple
access. The need for multiple access because more than two earth stations will be
present within the service area of a satellite. The important types of multiple access are.
➢ Frequency-Division Multiple Access (FDMA)
➢ Time-Division Multiple Access (TDMA)
➢ Demand Assigned Multiple Access (DAMA)
➢ Code-Division Multiple Access (CDMA)
➢ Space Division multiple Access (SDMA)
•These multiple access method can also be classified by the way in which the channels
are assigned to users, as below:
➢ Preassigned methods
➢ Demand-assigned methods
➢ Random-access methods.

Example for Fixed Assignment FDMA

Global Coverage by INTELSAT III

INTELSAT IV-A
• ❖ In order to increase the capacity of INTELSAT IV, in 1975 the first INTELSAT
IV- A satellite was launched.
• ❖ Capacity: ‘Frequencyre use’ was used to increase the capacity to 6000
telephone and 2 TV channels.

Comparison of INTELSAT satellites

• Star configuration
• Mesh Configuration

UNIT IV – SATELLITE ACCESS AND CODING METHODS
• Basic Modulation and Multiplexing: Voice, Data, Video, Analog – digital
transmission system, Digital video Broadcast, multiple access: FDMA, TDMA,
CDMA, DAMA Assignment Methods, compression – encryption, Coding
Schemes.

Modulation
• When information is to be conveyed over a satellite link, it is processed and
impressed on a radio frequency (RF) carrier. This process is called ‘modulation’.
• After transmission over satellite link, the modulated RF carrier is demodulate to
extract a replica of the original information.
• The choice of the modulation technique employed depends upon a range o
considerations.

The Telephone Speech Signal / Voice Signal
•The telephone speech signal is a type of audio signals. When a person speaks into a
telephone handset, the speech signal is converted into an electrical signal, because the
handset acts as the acoustic - to - electric transducer. These telephone speech signals
occupy bandwidths of upto20kHz.
Some important characteristics of the present telephone speech signal are given below.
❖ Bandwidth occupied : 300 - 3400Hz
❖ Nominal frequency spacing
Per channel : 4kHz
❖ Signal (test - tone ) -to -
Noise ratio : 50dB
❖ Interference levels
(below test - tone level) : 60-65dB
❖ Dynamic range required : ~45dB
❖ Speech activity
(average duty cycle) : 30-40%

Duty cycle:
Telephone talkers usually tend to pause between phrases and sentences. This is a very
important characteristic and due to this the active energy is concentrated in statistically
distributed talk spurts of 1.3s average duration. It is separated by quiet intervals and
pauses of upto 1 second.
Therefore, the average activity or duty cycle in the telephone speech signal is only
30% to 40% and thus the idle time is 60% to 70%
.
Digital transmission:
• If digital methods are used for transmission, two more parameters are needed to
determine the reconstructed quality of the speech signal. They are
1) Transmission rate (bits /second)
2) Bit Error Rate (BER)

ANALOG DIGITAL TRANSMISSION SYSTEMS
In satellite communications, two methods are used for the transmission of data or
telephony as well as video signals. They are
Analog and
Digital
Techniques Used:
1.Multiple Channel Per Carrier (MCPC) technique
2.Single Channel Per Carrier (SCPC) technique
Therefore, the analog techniques that are used in commercial satellite communications
for both telephony and video transmission and explained below are:
❖Amplitude Modulation (AM)
❖ Frequency-Division Multiplexing (FDM)
❖ Frequency Modulation (FM)

Frequency-Division Multiplexing (FDM)

Frequency Modulation (FM)
• Frequency modulation is a process in which the frequency of a sinusoidal carrier is
varied with the amplitude of the message or information signal.

DIGITAL TRANSMISSION SYSTEMS
•Digital technologies have gained wide acceptance today. In satellite communications,
digital transmission systems are used in both SCPC and MCPC applications.
Advantages:
1.Ruggedness
2.Security
3.Flexibility
4.Economy
5.Voice / Data / Video Integration
6.Compatibility with Switching machines
7.Power/bandwidthtrade-off

PCM Coder / Decoder (CODEC)
A PCM CODEC that is designed to convert the electrical analog speech wave form
into 8 – bit sequences and then reconstruct the analog signal from thE received bit
stream is shown in fig:

Coder:
❖ Input– a voice band signal occupying 4- kHz band width is applied as the input.
❖ Filter– the band pass filter that receives the input has a bandwidth of 300 to 3400
Hz. It band limits as well as adjusts the gain of the received input.
❖ Sampler–The filtered and gain - adjusted signal is then applied to a sampler.
➢ The sampler is provided with a sampling clock of frequency fs = 2fm
➢ Here, the instantaneous amplitude of the analog voice signal is determined at a
‘Nyquist rate’ of 8000 samples /s (i.e.8kHz rate). This is the standardized sampling rate
for telephone voice signals. Only if the signal is sampled at this rate, it can be
recovered without distortion.
➢ Sampling at any rate less than 2 fm (under sampling) results in an irremovable
➢ distortion called ‘aliasing’ in the reconstructed signal.
➢ Thus, the output of the sampler is a pulse amplitude modulated (PAM) waveform
with pulses occurring every 125μs.

Medium-Route Traffic
• Telesat Canadaoperates medium-route message facilities and utilizes
FDM/FM/FDMA. Fig shows how 168 voice channels are supported by five
carriers.
• The [G/T] ratio of fully loaded earth station = 37.5 dB/K
• The [G/T] ratio of partially loaded earth station = 28 dB/K Figure

INTELSAT SCPC Scheme
•In INTELSAT SCPC scheme,
❖ Quadrature phase-shift keying (QPSK) modulation is used.
❖ Transponder bandwidth is divided into 800 channels, each of 45 KHz wide
including guard band.
❖ Information may be digital data or PCM voice signals.
❖ Since pilot frequency is included, the scheme totally provides 798 one-way
channels.

FDMA DOWNLINK ANALYSIS
The effects of output backoff results from FDMA operation can be found considering
the overall carrier to noise ratio .
FDMA Carrier – to – Noise Ratio

TDMA
•In time division multiple access (TDMA) scheme, only a single carrier is allowed
access to the transponder at any given time. However, to allow all the users to access
the satellite, the transponder is time shared between users. Each user is allocated a
specific time slot for transmission. Thus, transmissions arrive at the satellite in a
sequence of non overlapping bursts. TDMA is compatible with only digital signals.
❖ The TWT can be operated at maximum power output or saturation level.
❖ They can be easily reconfigured for changing traffic demands.
❖ They are resistant to noise and interference
❖They can handle mixed voice, video and data traffic.
❖Since there is only one signal is present in the transponder at any time, the
intermodulation problem caused by non linear amplification of multiple carriers is
avoided.

Burst Synchronization
• The basic TDMA concept is shown in fig 5.22. It is necessary to synchronize each
and every burst. For this purpose, one reference station is assigned only for
transmitting reference bursts. All other bursts from other stations can be
synchronized with these reference bursts.

Principle of Burst Transmission:
• The burst-mode transmission for a single channel is illustrated in fig Eventhough
the transmission is digital, it seems to be continuous because, the input and output
bit rates are continuous and equal.
• Input bits are temporarily stored in buffers within the transmission channel. The
required buffer capacity is

Terrestrial Interface Modules (TIMs)

UPLINK POWER REQUIREMENT COMPARISON OF FDMAAND
TDMA
• The power requirements for FDMA and TDMA differ significantly.
FDMA:
• With FDMA, the modulated carriers are retransmitted from the satellite as a
combined frequency-division multiplexed signal as shown in fig The modulation of
the carrier may be analog or digital and it will not get affected in this case.

TDMA:
With, the uplink bursts are retransmitted as a combined time division multiplexed
signal as shown in fig:

ON-BOARD SIGNAL PROCESSING FOR FDMA/TDM
OPERATION
•FDMA/TDM operation is the hybrid mode operation which is explained in the
section In this method, the uplink FDMA signals are converted to TDM format for
downlink transmission using signal processing transponders. Because of this, the uplink
and downlink are decoupled and their performance is optimized independently.
The two important on-board signal processing methods are
➢ Conventional approach
➢Group processing

Group Processing
•In this method, a single processing unit demultiplexes all the input FDMA signals as a
group. All other processes are same as the conventional approach. This method may
require.
➢ Very High Speed Integrated Circuits (VHSIC) or
➢Surface Acoustic Wave (SAW) Fourier Transformer.
Advantage
Problem with processing each carrier separately can be avoided.

SATELLITE – SWITCHED TDMA (SS/TDMA)
• Satellite switched access is one of the advantages of TDMA. Instead of using a
single antenna beam to maintain continuous communication with its entire coverage
area, the satellite can use a number of narrow or spot antenna beams that are used
sequentially to cover the area.
• The use of spot beams is also known as space-division multiplexeing. It can
synchronize, the switching of antenna interconnections and the TDMA frame rate.
This method is known as satellite-switched TDMA (SS/TDMA).
Concept of SS/TDMA:
• The basic concept of SS/TDMA is shown in fig 4.31 in which three antenna spot
beams are used.

CODE DIVISION MULTIPLE ACCESS (CDMA)
• Code division multiple access is a scheme in which a number of users can occupy
all of the transponder bandwidth all the time. Therefore, individual carriers may be
present simultaneously, but each carrier has a unique code waveform in addition to
the information signal which helps to differentiate them at the receiver.
SSMA:
In CDMA, the carrier is first modulated by the information waveform and then it is
again modulated by the unique code waveform. The second modulation is done to
spread the spectrum over the available bandwidth. Therefore, CMDA is also known as
spread-spectrum multiple access (SSMA)

COMPRESSION AND ENCRYPTION
•MPEG
•MPEG is a group within the International Standards Organization and the
•International Electrochemical Commission (ISO/IEC). This ISO/IEC defines the
•standards for the transmission and storage of moving pictures and sound.
❖ These standards are concerned only with the bit stream syntax and the decoding
process.
❖ The syntax covers bit rate, picture resolution, time frames for audio and the
•packet details for transmission.
❖The currently available MPEG standards are MPEG -1, MPEG -2 , MPEG -4 and
MPEG – 7.
In DBS systems,
❖ MPEG – 2 → used for video compression
❖ MPEG – 1 →used for audio compression

UNIT IV – SATELLITE APPLICATION
Basic INTELSAT Series, INSAT, VSAT, Mobile satellite services: GSM, GPS,
INMARSAT, LEO, MEO, Satellite Navigational System. GPS Position Location
Principles, Differential GPS, Direct Broadcast satellites (DBS/DTH).

THE INTELSAT SERIES:
INTELSAT stands for ‘International Telecommunications Satellite’.
Features:
•INTELSAT organization was created in 1964 and in July 2001 it became a private
company.
• It has 140 member countries and more than 40 investing entities.
• In May 2002, the company started providing end - to - end solutions around the globe
through a network of teleports, leased fiber and points- of – presence i.e. PoPs.
• Starting from the year 1965, the organization has launched a series of satellites,
called the INTESAT Series to provide different services.

Regions Covered
The main regions covered by INTELSAT Satellites are
i.) Atlantic Ocean Region (AOR)
ii.) Indian Ocean Region (IOR)
iii.) Pacific Ocean Region (POR)
• In order to cover these ocean regions, the satellites are launched in geostationary
orbit and placed above the particular ocean. For example, INTELSAT 905 satellite
is positioned at 335.5∘east longitude.
INTELSAT Series:
A number of satellites are launched by the INTELSAT company with different features
and purposes. With each succeeding launch, it is understood by comparison that three
parameters were improved in the satellites. They are
i.) The number of voice channels
ii.) The capacity
iii.) The design lifetime

INTELSAT I:
❖ This satellite was launched in 1965 and it is known as ‘Early Bird’
❖ It was the first commercial communications satellite operating over the Atlantic
Ocean
❖ Type: Cylindrical, spin- stabilized satellite
❖ Antenna Type: Omni directional antenna
❖ Transponders: 2 transponders, each with 30 MHz bandwidth
❖ Power:
➢ RF transmit power = 4W
➢ EIRP (power * gain) = 12 to 14dBW
➢ 600 solar cells provided 45W power for all the circuitry
❖ Capacity: either 240 voice telephone circuits or one good-quality television
Transmission.
❖ Lifetime : designed life time was 18months, but extended to more than 3 years.

INTELSAT II:
❖ In 1967, three INTELSAT II satellites were put into operation
➢ First was placed over the Pacific Ocean to extend coverage
➢ Second was placed over the Atlantic Ocean to increase capacity
➢ Third was also placed over the Pacific Ocean to act as a spare.
❖ With these satellite over the Atlantic and Pacific, two third of the world‘s area was
covered by communication satellites.
❖ Its construction was very similar to Early Bird, but with improved channel
capacity
❖ Lifetime: designed lifetime was 3 years.

INTELSAT III
❖ During 1969, eight INTELSAT III satellites were launched over the Atlantic,
Pacific and Indian Oceans.
❖This made the first global satellite coverage possible as illustrated in fig
❖ Transponders: Each satellite had 2 transponders with 225 – MHz bandwidth
❖ Capacity: 1200 telephone channels, or 700 telephone channels plus one TV
channel
❖ Antenna: despun antenna was introduced. It is a highly directional antenna with a
beam width of 190∘ for global coverage.
❖ Lifetime: Due to some failures during launch and in orbit, only 3 satellites out of 8
were in service for the full design lifetime of 5 years.

INTELSAT IV and IV-A:
❖ During the period from 1971 to 1975, eight INTELSAT IV satellites were
launched, of which seven reached orbit and provided service.
❖ Transponders: each satellite had 12 transponder of 36 – MHz bandwidth, with 4
MHZ guard band.
❖Antennas: global coverage antennas and two 4.5∘beamwidth spot beam antennas.
One of the spot beams was directed to the east and the other to theest of an ocean
region to increase the capacity of heavy -traffic routes.
❖ Capacity: 4000 telephony channels plus 2 TV channels. ‗Frequency reuse‘ was
used to increase the capacity.

INTELSAT IV-A:
❖ In order to increase the capacity of INTELSAT IV, in 1975 the first INTELSAT IV-
A satellite was launched.
❖Capacity: ‘Frequencyre use’ was used to increase the capacity to 6000 telephone
and 2 TV channels. This is shown in fig

INTELSAT V and VA:
❖ It was launched in 1980.
❖ SatelliteType: three-axis body stabilized
❖ Newfeatures:
➢ use of 14 / 11 – GHz band with linear polarization
➢ TDMA was first introduced.
❖Power : Solar arrays on flat panels produced 1228W power (after 10 years in orbit)
INTELSAT VA:
➢ This was launched in the year, 1985, and designed to enhance bandwidth
utilization byusing frequency reuse techniques.
➢ Here, ‗onboardswitchinterconnection‘ between global, hemi, zone and spot beams
resulted in a flexible system that had a total channel bandwidth of 2250MHz.This was
achieved from the available bandwidth of 912MHz.

INSAT - INDIAN NATIONAL SATELLITE SYSTEM
❖ Indian National Satellite System (INSAT) is a series of multipurpose
Geostationary satellites launched by ISRO (Indian Space Research Organization) to
satisfy the telecommunications, broadcasting, meteorology, and search and rescue
needs of India.
❖ It is one of the largest domestic communication satellite systems in Asia-Pacific
region with nine operational communication satellites placed in Geo-stationary orbit.
❖ Established in 1983, INSAT is the largest domestic communication system in the
Asia Pacific Region. It is a joint venture of the Department of Space, Department of
Telecommunications, India Meteorological Department, All India Radio and
Doordarshan.
❖ The overall coordination and management of INSAT system rests with the
Secretary-level INSAT Coordination Committee.

INSAT system:
❖ The Indian National Satellite (INSAT) system was commissioned with the launch
of INSAT-1B in August 1983 (INSAT-1A, the first satellite was launched in April 1982
but could not fulfil the mission).
❖It initiated a major revolution in India‘s communications sector and sustained the
same later
❖ Together, the system provides 195 transponders in C, Extended C and Ku bands
for a variety of communication services in India.
❖ The satellites are monitored and controlled by Master Control Facilities that exist
in Hassan and Bhopal.

Basic Techniques
Accessing the hub from VSATs is a very complicated task. Some of the methods used
for this are:
1. Frequency-Division Multiple Access (FDMA)
2. Time-Division Multiple Access (TDMA)
3. Demand Assigned Multiple Access (DAMA)
4. Code-Division Multiple Access (CDMA)
1. Frequency Division Multiple Access
This is the most popular access method and it allows the use of low power terminals.
Time Division Multiple Access:
This method is not efficient for low density uplink traffic from the VSAT. If the traffic
is data transfer of a bursty nature, then TDMA mode leads to low channel occupancy.

•Demand Assigned Multiple Access:
This method is used in some systems where the channel capacity is assigned according
to the varying demands of the VSATs in the network. DAMA can be used with FDMA
and TDMA.
Disadvantages:
VSATs should make requests for channel allocation. For this purpose, a reserve channel
is needed to be established in this method and this channel should be accessed
efficiently.
Code Division Multiple Access:
This method is presented by Abramson (1990). It uses spread spectrum techniques with
the Aloha protocol.
Aloha Method
➢ This is a random access method.
➢ In this method, packets are transmitted at random in defined time slots.
➢ It is used where the packet time is smaller than the slot time.
➢ Packet collisions can also be dealt.
➢ It provides the highest throughput for small earth stations.
➢ This method is called ‗spread Aloha‘ by Abramson.

Network Configuration:
Two main configurations of the VSAT network are:
1. Star configuration
2. Mesh configuration
1. Star configuration
Here, the connection of one VSAT to another is made through a hub. So, a double hop
circuit is required. The topology of star network is shown in fig.

Mesh Configuration
In this configuration, the VSATs are connected to each other through the satellite in a
single hop. The topology of such a network is shown in fig

GSM – GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS
❖ GSM stands for Global System for Mobile Communications. It is a digital cellular
technology used for transmitting mobile voice and data services.
❖ Originally known as GroupeSpécial Mobile, is a standard developed by the
European Telecommunications Standards Institute (ETSI) to describe the protocols for
second-generation (2G) digital cellular networks used by mobile phones.
❖ It was established in 1982 and as of 2014 it has become the default global standard
for mobile communications.
❖ According to GSM World, there are now more than 2 billion GSM mobile phone
users in more than 210 countries throughout the world.

The Base Station Subsystem (BSS)
The BSS is composed of two parts:
➢ The Base Transceiver Station (BTS)
➢The Base Station Controller (BSC)

GPS – GLOBAL POSITIONING SYSTEM
• Global Positioning System (GPS) was created and realized by the US department of
defense (USDOD). GPS is a space-based global navigation satellite (GNSS) that
provides reliable location and time information.
• It works in all weather conditions and at all times and day where on or near the
earth. There are no subscription fee or setup charges to use GPS.
• GPS has become a widely deployed and useful tool for commerce, scientific uses,
tracking and surveillance.

INMARSAT - INTERNATIONAL MARITIME SATELLITE
• Inmarsat stands for International Maritime Satellite Organisation.
• It is a British satellite telecommunications company that was set up in 1979 by the
International Maritime Organization (IMO) to enable ships to stay in constant touch
with shore or to call for help in an emergency, no matter how far out to sea.
• It operates a constellation of 12 geostationarytelecommunications satellites,
called the INMARSAT SATELLITES that are designed to extend phone, fax and
data communications all over the world.
Services Provided:
INMARSAT satellites provide,

❖ telephoneand data services to users worldwide, via portable or mobile terminals
which communicate with ground stations.
❖ communications services to a range of government, aided agencies, media outlets
and businesses with a need to communicate in remote regions or where there is no
reliable terrestrial network.
❖connection to handheld satellite phones and notebook-size broadband
internetdevices, as well as specialist terminals and antennas fitted to ships, aircraft and
road vehicles.
❖Five different areas covered by these services are:
❖Inmarsat Maritime
❖Inmarsat U.S. Government
❖Inmarsat Global Government
❖Inmarsat Enterprise
❖Inmarsat Aviation

EC 8094 SATELLITE COMMUNICATION - COURSE MATERIAL

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