Transcript SATELLITE Communication

SATELLITE COMMUNICATION.
TOPICS COVERED.
Introduction.
Satellite Orbits.
Structure.
Frequency Allocation for Satellite Communication.
Working.
Advantages and Disadvantages.
Application.
INTRODUCTION.
• In satellite communication, the signal which is basically a beam of modulated
microwaves is sent from the sender towards the satellite. Then the satellite
amplifies the signal and sent it back to the receiver’s antenna present on the
earth’s surface.
• Satellites are important in: voice communications, video & radio transmission,
navigation (GPS), remote sensing (maps, weather satellites) etc.
HISTORY OF SATELLITE
COMMUNICATIONS
• For the first 20 years of satellite communications analog signals were widely used.
• Satellite communications began in October 1957 with the launch by the USSR a small
satellite called Sputnik 1
• First true communication satellites (Telstar I & II) were launched in July 1962 & May
1963
• 10/1964 Syncom2: First GEO satellite, 7.4/1.8 GHz (one TV-channel or several 2-way
telephone connections.
• 1987 TVSAT: First DBS-satellite (Direct Broadcast Satellite, Television broadcasts
directly to home).
SATELLITE ORBITS
One will always be in the sky for transmission of
communication signals.
HOW DOES A SATELLITE
STAY IN IT’S ORBIT?
DIFFERENT SATELLITES
REVOLVING AROUND THE
EARTH
TYPES OF ORBITS
LOW EARTH ORBITING
SATELLITES
• LEO satellites are much closer to the
earth ranging from 500 to 1500 km
above the surface.
• 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.
• Eg. Envisat.
MEDIUM EARTH ORBITING
SATELLITES
• MEO satellites have a larger
coverage area than LEO
satellites, ranging in altitude
from 2000 km to just below
GEO.
• A MEO satellite’s longer
duration of visibility and
wider footprint
• It’s distance gives it a longer
time delay and weaker signal
than a LEO satellite.
Eg. Telstar
GEOSTATIONARY EARTH
ORBITING SATELLITES
• Objects in GEO revolve around the
earth at the same speed as the
earth rotates.
• It’s long distance from
earth(approx 35,790km) cause it to
have both a comparatively weak
signal and a time delay in the
signal
• High transmit power needed and
launching of satellites to orbit are
complex and expensive
Eg. Syncom 3.
MOLNIYA ORBIT SATELLITES
• Used by Russia for decades.
• It is an elliptical orbit. The
satellite remains in a nearly
fixed position relative to
earth for 8 hours.
• Series of three Molniya
satellites can act like a GEO
satellite.
• Useful in near polar regions.
STRUCTURE OF SATELLITECOMMUNICATION.
WHAT ARE COMMUNICATION SATELLITES
COMPOSED OF?
• Communication Payload.
• Engines.
• Station.
• Power sub-system.
• Command and control sub-system.
COMMUNICATION PAYLOAD.
• Communication payload is made up of transponders,antennas and switching
systems.
• Transponder is a device which recieves radio signal and automatically
transmits into different signal.
TRANSPONDER.
Antenna is an electrical device which converts electrical power into radio
waves and vice-versa. It is usually used with radio transmitters or recievers.
ANTENNA.
• Engines are used to bring the satellites to the desired orbit.
• Station Keeping Tracking and stabilization subsystem used to keep the
satellite in the right orbit, with it’s antennas pointed in the right direction,
and it’s power system pointed towards the sun.
Engine.
• Power subsystem is used to power the Satellite system normally
composed of solar cells and batteries that maintain power during
solar eclipse.
Power
subsystem.
• Command and control subsystems maintain communications with
ground control stations. The ground control station monitors the
satellite performance and controls it’s functionality during various
phases of life-cycle.
Command and
Control subsystem.
FREQUENCY ALLOCATION FOR
SATELLITE SYSTEMS
Allocating frequencies to satellite services is a complicated process which
requires international coordination and planning.
This is carried out under the auspices of the International
Telecommunication Union (ITU).
 Although a given service may be allocated different frequency bands in
different regions.
Fixed satellite service (FSS)
Broadcasting satellite service (BSS)
Mobile satellite service
Radionavigation-satellite service
Meteorological-satellite service
Amateur-satellite service
HOW DO COMMUNICATIONS
SATELLITES WORK?
• Communications satellites receive
information from transmitters on Earth and
beam it down to receivers elsewhere on
the planet. Transmitters and receivers
differ widely.
• A communications satellite might relay a
signal between one sender and receiver,
satellite broadcasts typically involve one
or more uplinks and multiple downlinks.
ADVANTAGES OF SATELLITE
COMMUNICATION
• Flexibility:
• Mobility:
• Speedy deployment:
• Provides coverage over the globe:
DISADVANTAGES OF SATELLITE
COMMUNICATION
• Cost:
• Propagation delay:
• Specialised satellite terminals required:
APPLICATIONS OF
COMMUNICATION SATELLITES.
GLOBAL TELEPHONE
• Global Telephone One of the first applications of satellites for
communication was the establishment of international telephone backbones.
Instead of using cables it was sometimes faster to launch a new satellite.
• Telephonic conversations using satellites was not fruitful as the signal needs
to travel distance 10 times than the distance between 2 stations on the earth
i.e. sending data from ground to satellite and from satellite to another location
on earth. This cause’s substantial amount of delay and this delay becomes
more prominent for users during voice calls. The downlink follows an
analogous path. Improvements in submarine communications cables through
the use of fiber-optics caused some decline in the use of satellites for fixed
telephony in the late 20th century
GLOBAL MOBILE
COMMUNICATION
• Global Mobile Communication:-The
basic purpose of satellites for mobile
communication is to extend the area of
coverage. Satellites cover a certain area
on the earth. This area is termed as a
“footprint” of that satellite. Within the
footprint, communication with that
satellite is possible for mobile users.
These users communicate using a
Mobile-User-Link (MUL). The basestations communicate with satellites using
a Gateway-Link (GWL).
SATELLITE INTERNET ACCESS
• Satellite Internet access is
Internet access provided
through communications
satellites. Satellites have
brought Internet access to
places where IP
communications seemed
impossible.
RADIO AND TV BROADCAST
• Radio and TV Broadcast:- These
dedicated satellites are responsible for
making 100s of channels across the globe
available for everyone. They are also
responsible for broadcasting live
matches, news, world-wide radio services.
The signals are received via an outdoor
parabolic reflector antenna usually
referred to as a satellite dish and a lownoise block down converter (LNB).
Receivers can be external set-top boxes,
or a built-in television tuner.
AMATEUR RADIO
• Amateur radio (also called ham radio) describes the use of radio
frequency spectrum for purposes of non-commercial exchange of
messages, wireless experimentation, self-training, private recreation, radio
sport contesting, and emergency communication.
• The international symbol for amateur radio. The diamond holds a circuit
diagram featuring components common to every radio: an antenna,
inductor and ground.
NAVIGATION
• Navigation Satellites The system
allows for precise localization
world-wide, and with some
additional techniques, the
precision is in the range of some
meters.
CONNECTING REMOTE AREAS
• Connecting Remote Areas:- Due to their geographical location many
places all over the world do not have direct wired connection to the
telephone network or the internet (e.g., researchers on Antarctica) or
because of the current state of the infrastructure of a country. Here the
satellite provides a complete coverage and (generally) there is one
satellite always present across a horizon.
MILITARY APPLICATIONS.
• Communication satellites are used for military communications such as
Global Command and Control System.
• Military system that uses satellites for communication are MILSTAR,
DSCS, FLTSATCOM(USA), NATO satellites, Skynet(UK), and satellites
from Soviet Union.
• India has also launched a satellite for communication purpose of
military.
• The name of the satellite is GSAT-7. Transponders of this satellite
operate in UHF, F, C an Ku band.
THANK YOU.
Prepared by:
• Tejas Shah (15IT129)