23-11-2012, 01:36 PM
TRANSMISSION AND RECEPTION OF ANALOG AND DIGITAL SIGNALS USING OPTICAL FIBRE CABLE
TRANSMISSION AND RECEPTION.pptx (Size: 1.05 MB / Downloads: 39)
WHAT IS COMMUNICATION?
COMMUNICATION IS TRANSFERRING INFORMATION IN VARIOUS FORMS(TEXT,AUDIO,VIDEO) FROM ONE PLACE TO ANOTHER
THIS PROCESS NEEDS ATLEAST THREE ELEMENTS:AN INFORMATION SOURCE,A MEDIUM CARRYING INFORMATION TO A REMOTE POINT AND A SINK COLLECTING THE TRANSMITTED INFORMATION.
ANALOG COMMUNICATION MODEL
IT CONSISTS OF A MODULATOR, A MULTIPLXER FOR TRANSMISSION AT SOURCE AND A DEMODULATOR AND A DEMULTIPLEXER FOR RECEPTION AT THE SINK.
MEDIUM CAN BE AIR,COPPER CABLE OR AN OPTICAL FIBRE
WE WILL BE USING OPTICAL FIBRE CABLE AS A MEDIUM IN OUR PROJECT.
DIGITAL COMMUNICATION MODEL
IF INPUT IS IN FORM OF ANALOG SIGNAL IT IS CONVERTED INTO A BIT STREAM USING A PROPER A/D CONVERTOR.
STAGE TWO IS SOURCE CODING AND COMPRESSION WHICH IS USED TO REDUCE BIT RATE OF TRANSMISSION WHICH IS POSSIBLE DUE TO REDUNDANCY OF INFORMATION SOURCE
AT SOURCE CODING STAGE THE ENCRYPTION PROCESS MAY BE APPLIED,YIELDING THE SECURE BIT STREAM,WHICH MAY BE DECODED USING A SECRET KEY AT DECRYPTION STAGE.
ABOUT OPTICAL FIBRES
An optical fiber is constructed from a very thin stand of glass or ultra pure plastic that is incased in a cladding of glass or plastic with optical properties different from those of the inner core.
An outer jacket encases the cladding and core and guards them against moisture and damage.
DATA TRANSMISSION
Data is transmitted by sending pulses of light in the infrared or visible spectrums down the core of the fiber. As light enters the core it hits the edges of the core at a variety of angles.
The core material is designed to reflect light that hits at a relatively low angle. Light that hits the edge at a steep angle goes though and is absorbed by the jacket.
LIGHT SOURCES USED FOR SIGNALLING
Two different light sources are used for optical signaling. The Light Emitting Diode (LED) and the injection laser diode (ILD) are both semiconductor devices that emit light when supplied with a voltage.
The LED is cheaper and operates in less forgiving environments and lasts longer. In contrast, the ILD is more expensive and but can support higher data rates.