transmission of data by by rajesh chhetry

8/2/2019 Transmission of Data by by Rajesh Chhetry

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Transmission of Data/Voice

over Fiber-Optic link

By Rajesh Chhetry


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Objective

The main objective of this paper is to make

a comparative study among different

principles ,technologies and practices thatinvolve in the transmission of data over

fiber optic link and recommend a

communication system that perfectly meetsthe requirements of communication of data

in the current trend and environment.


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Introduction

In recent years it has become apparent that

fiber-optics are steadily replacing copper

wire as an appropriate means ofcommunication signal transmission

They span the long distances between local

phone systems as well as providing thebackbone for many network systems


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This paper is about the different principles

involved in a fiber optic communication.


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Fiber Optic technology

fiber-optics use light pulses to transmit

information down fiber lines

The transmitter accepts coded electronic

pulse information coming from copper wire

The information is then processed and

translated into equivalently coded lightpulses.


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A light-emitting diode (LED) or an

injection-laser diode (ILD) can be used for

generating the light pulses .

Light pulses move easily down the fiber-

optic line because of a principle known as

total internal reflection


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Elements of Optical fiber cable

The optic core

An optic cladding,

A buffer material,

A strength material

The outer jacket


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Fiber optic applications

(Data) Backbone architechture for

telecommunication links

Cable service providers /High speed internet

Trunk lines

Monitor power grid systems

Local area networks


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Fiber optics economics

One of the initial economic factors to consider

when converting to fiber-optics is the cost of

replacing wire systems with fiber Increased demand for optical fiber has brought the

prices down within competitive range of copper

In the short term it is often less expensive to

continue using copper cabling for covering

expanded communication needs


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In the long term it may be more cost effective to

invest in conversion to fiber-optics .

This cost effectiveness is due to the relative easeof upgrading fiber optics to higher speeds and

performance.

It is generally accepted that customers will need

increased bandwidth as the information highway

grows


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Fiber optics will play a pivotal role in this

race since the bandwidth needed for

providing an all-in-one service withtelevision, telephone, interactive

multimedia, and internet access is not

available in much of the wiring of America.


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Single Mode and multimode

fibers Single mode allows

only one mode of ray

to pass through itscore.

Multi- mode allows

hundreds of rays of

light to propagatethrough the core.


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Encoding

The source information (such as audio,video or sonar) comes in many forms .

The first step is to convert the informationinto a bit-stream .

once the information is stored electronically

and whatever the form, data can beconverted into raw binary data prior totransmission.


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Base Band Modulation

The next step is to modulate the baseband

and this is where, in constructing an optical

communications system, we start makingcompromise .

Different modulation schemes make

varying use of the bandwidth, but the trade-offs will include distance, compression,

BER and power.


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Due to the lack of 'coherent' optical systems

for extracting phase information, optical

communication systems use pulse codemodulation (PCM) schemes to modulate the

baseband .

There are many PCM techniquesavailable.HDB3 is the most advanced and

efficient technique developed so far.


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HDB3


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Light Sources

Leds- produce incoherent light that severely

reduces the obtainable bandwidth .

Laser Diodes-Lasers produce coherent light

and deliver far higher performance than

LEDs e.g Fabryperot laser


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Recommendations

With reference to the study about the fiber opticssystems , the following communication systemcan be recommended for an efficient and reliabledata transmission.

Fabry- perot laser diode

Pulse code modulation technique used for

producing bit streams Encoded using HDB3 codes

Single Mode step index fiber


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This can be a solution for the requirement

of the data-ondemand system

implemented by businesses today.

The requirement for such a system is high

Bandwidth.


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Summary

Based on industry activity, it is evident that

fiber-optics have become the industry

standard for transmission of information.The choice is not whether to convert to

optical fiber, but rather when to convert to

optical fiber. It is most likely that we will beable to use it in our local networks in the

days to come.


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encoding techniquesencoding techniques

PCM: pulse code modulation

samples of the analog data taken each sample quantized

samples transmited as digital signal

received samples used to reconstruct analog data

example: voice channels

samples taken 8000/sec

quantized to 7 bits

synch. bit added -> 8 bits

8 x 8000 = 64000 bps, standard digital voice channel

transmission of data by by rajesh chhetry

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