Satellite communication

SATELLITE COMMUNICATION – an Overview

A TECHNICAL SEMINARBY

V sasank chaitanya kumar,

Topics of presentation

introduction

Types of

satellites

Frequency

bands

Where these

are placed

Working

princple

application

s

SATELLITE

Introduction

The never ending quest of communication engineer is to transmit maximum information in short time to the largest possible distance,this gave raise to many systems of communications.

Disadvantages of exisiting broad band methods:

Coaxial cables,Fiberoptics - Wiring problem Microwaves - LOS

Defination of satellite

Satellite can be defined as a heavy object which goes around object in space due to the effect of mutual gravitational forces,used for broadband communication.

Why satellites came into picture??

This is because the earth is like a sphere As we know radio waves travel in straight lines at micro wave frequenices A repeater is needed to convey signal over long distance Satellites are used to link places on earth that are thousands of

miles a part

Need of satellite for long distance communication

Types of Satellites Active satellite It is one in which the signal is amplified and its frequency changed by transponder,before itsent back to earth. Example:communication,broadcasting satellites

Passive satellite These type of satellites simply reflects or scatters the micro wave signal back to another station Example:military and non profitable servieces

Satellite pictures

October 1957, the first artificial satellite Sputnik -I was launched by former Soviet Russia.

The first artificial passive satellite Echo-I of NASA was launched in August 1960.

In July 1962 active satellite Telstar was developed and launched

Advantages of Satellites

The advantages of satellite communication over terrestrial communication are:

The coverage area of a satellite greatly exceeds that of a terrestrial system.

Transmission cost of a satellite is independent of the distance from the center of the coverage area.

Higher Bandwidths are available for use.

Disadvantages of Satellites

Launching satellites into orbit is costly.

Satellite bandwidth is gradually becoming used up.

There is a larger propagation delay in satellite communication than in terrestrial communication.

Satellite Transmission Bands

The C band is the most frequently used. The Ka and Ku bands are reserved exclusively for satellite communication but are subject to rain attenuation

Frequency Band Downlink Uplink

C 3.7-4.2 GHz 5.92-6.42 GHz

Ku 11.7-12.2 GHz 14.0-14.5 GHz

Ka 17.7-21.2 GHz 27.5-31.0 GHz

Types of Satellite Orbits 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°)

Based on Eccentricity Circular with centre at the earth’s centre Elliptical with one foci at earth’s centre

What is Apogee and Perigee?

Where satellites are placed?

Satellite orbits are also classified in terms of the orbital height. These are:

Breif overview of orbits

s1

s2 s3

ELEMENTS OF SATELLITE COMMUNICATIONS SYSTEM

Two major elements of Satellite Communications Systems are: Space Segment Ground Segment

The Space Segment includes: Means for launching satellite Satellite(Transponders) Power supply system

The ground segment consists of: Earth Stations Rear Ward Communication links

DVB-RCS

Outbound subscriber(target of interest)

Gateway stationCentral Hub

SatMon station

Functioning of Transponder

TO /FROMEARTH STATION

Power requriment

Modern satellites use a variety of power means

Solar panels are now quite efficient, so solar power is used to generate electricity

Batteries are needed as sometimes the satellites are behind the earth - this happens about half the time for a LEO satellite

Nuclear power has been used - but not recommended

Earth Station Block diagram

Earth stations

SATELLITE COMMUNICATION SERVICES

Different Satellite Communications services are classified as one way link Two way link.

One way link from transmitter Tx to receiver Rx on earth’s surface

Broadcast Satellite Service (Radio, TV, Data broadcasting)

Data Collection Service (Hydro meteorological data collection)

Space operations service, (Tracking, Telemetry, Command)

Safety services (Search & Rescue, Disaster Warning)

Earth Exploration Satellite Service (Remote Sensing)

Radio Determination Satellite Service (Position location)

Reporting Service (fleet monitoring)

Examples of satellite services where the transfer of information takes place through one way link are:

Two-way Satellite Communications link

Fixed Satellite Service (Telephone, telex, fax, high bit rate data etc.)

Mobile Satellite Service (Land mobile, Maritime, Aero-mobile, personal communications)

Satellite News Gathering (Transportable and Portable )

04/10/23 By DeepakPoonamsasank

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