Chapter : Unguided/Wireless Media, PPT, Semester, Engineering - Computer Science Engineering (CSE) PDF Download

Unguided/Wireless Media

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Unguided/Wireless Media

Ways Of Transmit Signals

Radio Communication Band

Satellite Transmission

Laser/Light Wave 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 of capable of receiving them.
Ranges from 3kHz to 900 THz.
Radio, Microwave and Satellite.

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Ways Of Transmit Signals

Ground Propagation
Sky Propagation
And, Line of Sight Propagation

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Ground Propagation

Radiowaves travel through lowest portion of atmosphere close to the earth.
These are LF signals that travel in all the directions from transmitting antenna and follow the curvature of earth.
More the Power = More the Distance covered.
For e.g. Radio Transmission (Akashwani Jalandhar.)

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Sky Propagation

HF radiowaves are sent upward into ionosphere.
From ionosphere these signals are reflected back to the surface of earth.
Less Power is needed and IONS are present in Ionosphere.

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Line Of Sight Propagation

It uses VHF signals that are transmitted in a straight line path from one antenna to another.
It requires proper placement of antennas in terms of their heights and distance.
For e.g. Mobile Towers

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Propagation Types

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Radio Communication Band

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Frequency Range

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Frequency Range…

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Radio Wave Transmission

The radio wave have frequencies between 3kHz and 1GHz.
Radiowaves are omni directional.
These waves can penetrate through buildings.
Radio waves are subject to interferences from motors and other electrical equipments.
They are also absorbed by rain.
In VLF, LF, MF bands radiowaves follow the ground.
In HF and VHF bands radiowaves are send upward into ionosphere where they are reflected back to earth.
Radio waves are widely used for AM and FM radio, Television, Cellular Phones and Wireless LAN.

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RadioWaves Transmission...

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Microwave Transmission

These are electromagnetic waves having frequencies between 1GHz and 300 GHz.
There are two types of microwave transmission:
◦Terrestrial
◦Satellite

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Terrestrial Microwave System

It is unidirectional i.e. travel in straight line.
Repeaters are required to strengthen the signals.
Requires line of sight propagation.
Distance covered by a line of sight signal depends upon the height of antenna.
In it Transceivers are used which are capable of both transmitting and receiving the signals.
Very high frequency microwaves cannot penetrate walls.
High data rate transfer should be possible due to its relatively wide band property, almost 299 GHz and that needs permission to use from government authorities.
Mainly used for one to one communication.
For. e.g. Campus 1 connected with Campus 2 with Microwave Antennas or Mobile Tower 1 to Mobile Tower 2.

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Terrestrial Microwave

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Parabolic Dish Antenna

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Horn Antenna

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Satellite Transmission

A satellite is a body that revolves around the earth.
Natural or Artificial/Man-made
Man-made satellites are used for communication purposes .
The paths in which satellites move are called Orbits.
A communication satellite acts as a big microwave repeater in the sky.
Satellite communication makes use of Geostationary satellites (placed at 36,000 km approx. above equator Exact=35,800).
Geostationary satellite contains many Transponders i.e. receives signals from 1 earth station, Amplifies it and sends the signal back to other earth station.
Signal Transmitted upward to satellite = UPLINK.
Signal Transmitted back to receiving earth station= DOWNLINK.
Both UPLINK & DOWNLINK frequencies are different

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Satellite Communication

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Infrared Waves

Electromagnetic waves having frequencies from 300 GHz to 400 THz.
They are used for short range communication and use line of sight propagation.
Infrared waves cannot pass through solid objects like walls (disadvantage).
IR waves offer very large bandwidth for use.
For e.g. Remote controls used for TV, DVD players, Communication between keyboard, mouse, printers.

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Laser/Light Wave Transmission

It uses thin laser beams to transfer data up to few kilometers.
It is unidirectional and uses line of sight propagation.
In this a photo detector and laser is set up on both send and receiver side.
High bandwidth at a very low cost.
For e.g. Escalators.

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Geosynchronous Orbit