SATELLITE NETWORKSPresented by:

Krishna Kant Gupta

Semester: 6th Roll no.: 16Computer

Networks (IT-604)Year: 2013

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• Introduction• Artificial Satellites over Natural Satellites• Orbits• Types Of Satellite Orbits• Footprint• Categories of Satellitei. GEOii. MEOiii. LEO• Advantages of Satellites• Disadvantages of Satellites

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CONTENTS

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INTRODUCTION

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We can install electronic equipment on the satellite to regenerate the signal that has lost its energy during travel.

The distance of natural satellites, such as the Moon, from the Earth is huge, which create a long delay in communication.

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ARTIFICIAL SATELLITES OVER NATURAL ONE’S

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An artificial satellite needs to have an orbit, the path in which it travels around the Earth.

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SATELLITE ORBITS

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Kepler’s Law: It determines the period of satellite.

Period = C x distance1.5 sec.

Note:

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Example 1

What is the period of the moon according to Kepler’s law?

Solution

The moon is located approximately 384,000 km above the earth. The radius of the earth is 6378 km. Applying the formula, we getPeriod = (1/100) (384,000 + 6378)1.5 = 2,439,090s = approx.(1 month)

Distance: 384000 kmPeriod: approx. 1month

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Example 2

According to Kepler’s law, what is the period of a satellite that is located at an orbit approximately 35,786 km above the earth?Solution

Applying the formula, we get

Period = (1/100) (35,786 + 6378)1.5 = 86,579 s = 24 h

A satellite like this is said to be stationary to the earth. The orbit, as we will see, is called a geosynchronous orbit.

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The area of the Earth’s surface from which an Earth Station can transmit to or receive from a particular satellite.

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FOOTPRINT

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Sate

llite GEO

MEO

LEO

Based on the location of the orbits satellites are divided into three categories:

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SATELLITE CATEGORIES

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Outer Van Allen Belt (15000-20000 km)

MEO (5 - 15K km)

GEO (35786 km)

LEO ( < 2K km)

Inner Van Allen Belt (1500-5000 km)

GEO: Geostationary Earth Orbit

MEO: Medium Earth Orbit

LEO: Low Earth Orbit

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SATELLITE ORBIT ALTITUDES

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• Two Stations on Earth want to communicate through radio broadcast but are too far away to use conventional means.

• One Earth Station sends a transmission to the satellite. This is called a Uplink.

• The satellite Transponder converts the signal and sends it down to the second earth station. This is called a Downlink.04/09/2023 08:40:06 PM

HOW SATELLITE WORKS?

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Band Downlink, GHz

Uplink, GHz

Bandwidth, MHz Problems

L 1.5 1.6 15 Low bandwidth; crowded

S 1.9 2.2 70 Low bandwidth; crowded

C 4.0 6.0 500 Terrestrial Interference

Ku 11.0 14.0 500 Rain

Ka 20.0 30.0 3500 Rain, equipment costL-band and S-band: is used for Mobile Satellite Services and offers good penetration through adverse weather conditions and foliage.

C-band: Public switched networks.

Ku-band and Ka-band: Rural telephony, satellite news gathering, high speed internet, video conferenc ing, and multimedia.

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SATELLITE FREQUENCY BAND

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These satellites are in orbit 35,786 km above the earth’s surface along the equator.

Objects in Geostationary orbit revolve around the earth at the same speed as the earth rotates. This means GEO satellites remain in the same position relative to the surface of earth.

One GEO satellite cannot cover the whole earth. It takes minimum of three satellites equidistant from each other.

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GEOSTATIONARY EARTH ORBIT (GEO)

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SATELLITES IN GEOSTATIONARY ORBIT

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• Advantages

A GEO satellite’s distance from earth gives it a large coverage area, almost a fourth of the earth’s surface.

GEO satellites have a 24 hour view of a particular area.

These factors make it ideal for satellite broadcast and other multipoint applications.

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GEO (CONT.)

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• Disadvantages

A GEO satellite’s distance also cause it to have both a comparatively weak signal and a time delay in the signal, which is bad for point to point communication.

GEO satellites, centered above the equator, have difficulty broadcasting signals to near polar regions

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GEO (CONT.)

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• A MEO satellite is in orbit somewhere between 5,000 km and 15,000 km above the earth’s surface.

• MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 to 8 hours.

• MEO satellites have a larger coverage area than LEO satellites.

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MIDDLE EARTH ORBIT (MEO)

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• Advantages A MEO satellite’s longer duration of visibility and wider

footprint means fewer satellites are needed in a MEO network than a LEO network.

Shorter time delay and stronger signal than a GEO satellite

• Disadvantages A MEO satellite’s distance gives it a longer time delay and

weaker signal than a LEO satellite, though not as bad as a GEO satellite.

EXAMPLE: Global Positioning System (GPS). 04/09/2023 08:40:07 PM

MEO (CONT.)

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• Constructed and operated by US Department of Defense.

• There are 24 satellites in six orbits.

• Used for land, sea and air navigation to provide time and locations for vehicles and ships.

• The satellites in each orbits are designed in such a way, at a time minimum four satellites are visible from any point on the Earth.

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GPS: EXAMPLE OF MEO

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ORBITS FOR GPS SATELLITE

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TRILATERATION

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• Measuring the distance: The trilateration principle can find our location on the earth if we know our distance from three satellites and know the position of each satellite. The position of each satellite can be calculated by a GPS receiver. The GPS receiver, then, needs to find its distance from at least three GPS satellites. Suppose all GPS satellites and the receiver on the earth are synchronized. Each of 24 satellites transmits a complex signal each having a unique pattern. The receiver measures the delay between the signals from the satellites and its copy of signals to determine the distances to the satellites.

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GPS: HOW IT WORKS ( CONT.)

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• LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to 2000 km above the surface.

• Rotation period of 90 to 120 minutes, with speed 20,000 to 25,000 km/h.

• LEO satellites 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.

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LOW EARTH ORBIT (LEO)

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LEO SATELLITE SYSTEM

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• Advantages

A LEO satellite is proximity to earth compared to a GEO satellite gives it a better signal strength and less of a time delay, which makes it better for point to point communication.

A LEO satellite’s smaller area of coverage is less of a waste of bandwidth.

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LEO (CONT.)

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• Disadvantages

A network of LEO satellites is needed, which can be costly

Atmospheric drag effects LEO satellites, causing gradual orbital deterioration.

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LEO (CONT.)

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• It has 66 satellites in 6 LEO orbits.• Each have altitude of 750 km.• Use to provide direct worldwide communication. i.e. voice, data paging, fax, even navigation.

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IRIDIUM SYSTEM: EXAMPLE OF LEO

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The original name, Iridium, came from the name of the 77th chemical element; a more appropriate

name is Dysprosium (66th element)

Fact:

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• It has 48 satellites in 6 LEO orbits.• Each have altitude of 1400 km.• The ground station can create more powerful signals.

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GLOBALSTAR: EXAMPLE OF LEO

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•It provides fiber-optic like (broadband channels, low error rate, and low delay) communication •It has 288 satellites in 12 LEO polar orbits.• Each have altitude of 1350 km.

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TELEDESIC: EXAMPLE OF LEO

The project was started in 1990 by mobile phone pioneer Craig McCaw and Microsoft founder Bill Gates.

About:

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The goal of Teledesic system is to provide broadband Internet access for users all over the world

Goal:

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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.

Satellite to Satellite communication is very precise. Higher Bandwidths are available for use.

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ADVANTAGES OF SATELLITES

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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.

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DISADVANTAGES OF SATELLITES

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THANK YOU....

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