WIRELESS TRANSMISSION

WIRELESS or UNGUIDED TRANSMISSION

• Wireless media transports electromagnetic waves without using a physical conductor.
• Signals are broadcast through air and are available to anyone who has a device capable of receiving them.

ELECTROMAGNETIC SPECTRUM

VARIOUS WAYS FOR SIGNAL TRAVELLING

1. GROUND PROPAGATION –

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• Radio waves travel through lowest portion of atmosphere close to the Earth.

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• These signals are travel in all directions from transmitting Antenna and follow the curvature of earth.

VARIOUS WAYS

2. SKY PROPAGATION –

• The high frequency radio waves are radiated upwards into ionosphere.

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• These signals from ionosphere are reflected back to the surfaces of earth.

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• Ionosphere is the atmosphere layer where particles exist as ions.

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VARIOUS WAYS

3. LINE-OF-SIGHT PROPAGATION –

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• These propagation uses high frequency signals that are transmitted in a straight line path from Antenna to another.

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• It requires proper placement of Antennas in terms of their heights and distance.

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Note: The frequency range of 3KHz-300GHz used for radio,microwaves and satellites transmission is divided into 8 ranges called BANDS.

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RADIOWAVES TRANSMISSION

• The radio waves have frequencies between 3KHz and 1GHz.
• Radio waves can penetrate buildings easily ,so they are widely use for communication both indoors outdoors.

RADIOWAVES TRANSMISSION

RADIOWAVES TRANSMISSION

• The radio waves can travel long distance. At low frequency ,radio waves pass through obstacles.

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• In VLF,LF and MF bands ,radio waves follow the Ground.

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• In VHF and HF bands , radio waves are radiated upwards into ionosphere .

MICROWAVE TRANSMISSION

• Micro waves are electromagnetic waves having frequencies between 1GHz and 300GHz.

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• There are two types of microwave data communication systems –

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TERRESTIAL MICROWAVES

• The microwaves always travels in a straight line from source to destination.

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• Each frequency must have its own transmitter and receiver .

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• Micro waves require line-of-sight propagation.

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TERRESTIAL MIOWAVES

TERRESTIAL MICROWAVES

• High frequency microwaves are enable to penetrate into walls.

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• The microwave bands are 299GHz wide. Now days a device called Transceivers are used for data transmission .

• Microwaves are widely used for one to one communication known as Unicast communication.

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INFRARED WAVES TRANSMISSION

• Infrared waves having frequencies from 300GHz to 400THz.

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• These waves are also called IR waves .

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• These waves are used for short range data communication and use line-of-sight propagation.

INFRARED WAVES TRANSMISSION

INFRARED WAVES TRANSMISSION

• Infrared waves cannot pass through solid objects , like walls and can be easily contained in a room .
• They are cheap , easy to build and do not require any government license to use them.
• Security system of IR system against eavesdropping(secretly listen to a conversation) is better then radio waves.

LIGHT WAVE TRANSMISSION

• This type of transmission uses thin laser beams to transfer data upto few kilometers.

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• This type of transmission system uses line-of-sight propagation.

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• The major problem in this transmission system is that laser beams cannot penetrate rain or thick fog.

LIGHT WAVE TRANSMISSION

LIGHT WAVE TRANSMISSION

• These systems provide very high bandwidth at a very low cost.

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• A photo detector and laser is set up on both sender and receiver side .

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• A laser transmission system is the connection between two LAN’s operating in two separate buildings.

SATELLITE TRANSMISSION

• A satellite is a body that revolves around the earth just in same way earth revolves around the sun .

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• A satellite can be natural such as moon or it can be artificial/manmade(created by human).

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• The paths in which satellite moves is called Orbit.

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• The signal from a satellite is normally aimed at a specific area called footprint . The signal power at the center of footprint is maximum.

SATELLITE TRANSMISSION

SATELLITE TRANSMISSION

• The signals transmit from earth station to satellite are called uplink frequency.

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• The signals transmit from satellite to earth station are called downlink frequency.

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• The transponder receives signal from one earth station, amplifies it and sends back to other earth station .

GEO- SATELLITE

• This ensures constant communication and the satellite seems to remain fixed above a certain spot.

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• As the orbital speed depends on the distance from the planet, only one orbit can be geo- stationary.

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• It takes a minimum of three satellites equidistant from each other in geo- stationary earth orbit to –provide full global transmission.

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• The view is from north pole.

MEO-SATELLITE

• MEO satellites take approximately 6-8 hours to circle the earth.

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• Examples of MEO satellites is GLOBAL POSITIONING SYSTEM (GPS).

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• MEO satellite lies at lower altitudes between the two Van Allen belts.

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• GPS satellites orbit at about 18,000 km above the earth .

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LEO- SATELLITE

• The LEO-satellite lies at an altitude between 500 and 2000km and have polar orbits.
• The speed of LEO satellite is 20,000 to 25,000 km/h.
• The footprint has a diameter of 8000 kms.
• As these satellite are very close to the earth the ground stations do not need much power and the round trip propagation delay is less than 20 msec.
• A LEO system consists a number of satellites that works together as a network.

LEO SATELLITE TYPES

• LITTLE-LEO: These are operates under 1GHz.They are used for low-data-sate messaging.

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• BIG-LEO: These are operates under I and 3GHz. Examples are Globalstar and Iridium system.

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• BROADBAND-LEO: These satellites provide communication similar to fiber optic networks. Example is Teleodesic.

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