lab 1 by mehran mamonai. a satellite is a radiofrequency repeater but new-generation satellites are...

Introduction to Satellite Communication

Lab 1

ByMehran Mamonai

OVERVIEW

A satellite is a radiofrequency repeater but New-generation satellites are regenerative.

Satellite amplify, conditions and reformat received (uplink) data and route (downlink) the data to specified locations.

Reformatting is done in Transponder. Satellite moves in different orbits. Satellite has vast number of Applications. Limitation in Satellite.

THE ORIGIN OF SATELLITES

U.S.S.R.’s launch of the first artificial satellite called Sputnik (1957).

Worked only for 21 days as Telemetry services.

The first series of commercial geostationary satellites was inaugurated in 1965

COMMUNICATIONS VIA SATELLITE

High Frequency Radio waves were used as carriers of information with a large bandwidth

Earth to Satellite Frequency is called Uplink

Satellite to Earth Frequency is called Downlink

Reception area called footprint (covering map)

Example of Foot Print

Basic Transponder Arrangement

Transmitter and Responder = Transponder

Equivalent Isotropic Radiated Power (EIRP)

The satellites are characterized by the power they radiate in the beam axis

This corresponds to the power (expressed in dBW)

Types of Satellites (Orbit wise)

Geostationary satellite (GEO) High elliptical orbiting satellite (HEO) Middle-earth orbiting satellite (MEO) Low-earth-orbiting satellite (LEO)

Geostationary satellite (GEO)

All satellite occupies an orbit around the ground located at about 36,000 km (35785) height

satellite speed coincides to the earth rotation speed.

Also called Geosyncronous.

High Elliptical (Earth) Orbit (HEO)

An HEO satellite is a specialized orbit satellite continuously swings very

close to the earth, loops out into space, and then repeats

It is an elliptical orbit approximately 18,000 to 35,000 km above the earth’s surface

Not necessarily above the equator

Middle (Medium) Earth Orbit (MEO)

Satellite orbiting approximately 8,000 to 18,000 km above the earth’s surface

Not necessarily above the equator between the LEO and GEO

Low Earth Orbit (LEO)

 Orbit between altitude of approximately 160km to 2,000 kilometers

 Majority of artificial satellites, have been in LEO.

Satellite cannot orbit less than 300 km due to the larger atmospheric drag.

Lowest Delay then orbit MEO and GEO.

Orbits around Earth scale diagram

Frequency sub-division

C – band Up-link: from about 5.7GHz to about 6.5GHz Down-link: from 3.4GHz to 4.2GHz

Ku – band: Up-link: from about 14GHz to about 14.5GHz Down-link: from 10.95GHz to about 12.75GHz, with the

following sub-division: 10.95 – 11.70GHz FSS band (Fixed Satellite Services) for

TV communication 11.70 – 12.50GHz DBS band (Direct Broadcasting

Satellite) for direct diffusion 12.50 – 12.75GHz SMS band (Satellite Mobile Services)

Communication Satellite Frequency Bands Allocation

Polarization

More channels on the same band Polarity formats

Linear▪ Horizontal▪ Vertical

Circular▪ LHCP▪ RHCP

Polarization (Example)

Broadcasting and coding standards

Frequency modulated by the Video + Audio composite signal

PAL NTSC SECAM MAC

Superior clearness of the digital superior to the 50% in respect to PAL

Frequency Modulated (PAL,

NTSC, SECAM)

Digital Video Broadcasting-Satellite (DVB-S)

Employs the QPSK digital modulation