dc-lec-13 (intro to encoding techniques)

8/3/2019 DC-Lec-13 (Intro to Encoding Techniques)

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DATACOMMUNICATION

Lecture-13


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Recap of Lecture 11 & 12Recap of Lecture 11 & 12

Signals

Analog and Digital

Analog and Digital Data & Signals

Periodic & Aperiodic Signals

Sine Waves and its Characteristics

Control of Signals

Time and Frequency Domain

Composite Signals


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Overview of Lecture 13Overview of Lecture 13

Introduction to the Encoding Techniques

Digital-To-Digital Encoding

Types of Digital-To-Digital Encoding


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IntroductionIntroduction

Information must be transformed intosignals before it can be transferred acrossthe communication media.

How this information is transformeddepends upon its original format and onthe format of the communication hardware.


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Conversion MethodsConversion Methods


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Digital-to-Digital ConversionDigital-to-Digital Conversion

Digital-to-Digital conversion/encoding is therepresentation of digital information by

digital signal.

For Example:When you transmit data from Computer to the

Printer, both original and transmitted data haveto be digital.


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Digital-to-Digital ConversionDigital-to-Digital Conversion


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Types of Digital-to-DigitalTypes of Digital-to-Digital

EncodingEncoding

Digital/Digital Encoding

Uni-polar Polar Bipolar


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Unipolar EncodingUnipolar Encoding

Simple and Primitive.

Almost Absolute Today.

Uses only one polarity level (this polarity isassigned to one of the binary state, usually1, 0 is represented by zero voltage.

Study provides introduction to concepts and

problems involved with more complexencoding systems.


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Unipolar EncodingUnipolar Encoding


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Pros and Cons of UnipolarPros and Cons of Unipolar

EncodingEncoding

PROS

Straight Forward and SimpleInexpensive to Implement


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Pros and Cons of UnipolarPros and Cons of Unipolar

EncodingEncoding CONS DC Component(the average amplitude

of uni-polar encoded signal is non-zero)

Synchronization(if the data contain longsequence of 0s and 1s, there is nochange in the signal, during thisduration that can alert the receiver topotential synchronization problem)


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Polar EncodingPolar Encoding

Polar encoding uses two voltage levels

One positive and one negative

Average voltage level on the line isreduced

DC Component problem of Unipolarencoding is alleviated


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Types of Polar EncodingTypes of Polar Encoding


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Non Return to Zero (NRZ)Non Return to Zero (NRZ)

The level of signal is either positive ornegative

NRZ

NRZ-L NRZ-I


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Non Return to Zero-Level (NRZ-L)Non Return to Zero-Level (NRZ-L)


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Non Return to Zero-LevelNon Return to Zero-Level

(NRZ-L)(NRZ-L) Positive voltage usually means the bit is

zero 0.

Negative voltage usually means the bit isone 1.

Synchronization problem (in case ofcontinuous 1s or 0s)


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Non Return to Zero-Invert (NRZ-I)Non Return to Zero-Invert (NRZ-I)

Inverse of NRZ-L

In this the 1 bit is used for transition, notused for voltage representation.

0 represent no change.

NRZ-I is superior to NRZ-L due tosynchronization provided by signal change

each time 1 bit is encountered. The string of 0 can still cause problem,

but 0 do not occur mostly.


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Non Return to Zero-Invert (NRZ-I)Non Return to Zero-Invert (NRZ-I)


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Return to Zero (RZ)Return to Zero (RZ)

Synchronization problem is present inother encoding schemes which wassomewhat eliminated by NRZ-I, but stillthe problem was there with theconsecutive 0s.

So the solution was provided by RZ aschange on every bit.

Three values were used i.e. Positive Negative

Zero.


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Signal changes between mid of bit.

1 is represented by positive-to-zero.

0 is represented by negative-to-zero.

Disadvantage is that it requires two signalchanges to encode one bit therefore

occupies more bandwidth.


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Biphase EncodingBiphase Encoding

Best existing solution to the problem ofSynchronization

Signal changes at the middle of bitinterval but does not stop at zero


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Biphase EncodingBiphase Encoding

Biphase

Encoding

DifferentialManchesterManchester


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ManchesterManchester


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ManchesterManchester

Uses an inversion at the middle of each bitinterval for both synchronization and bit

representation. 1 is represented by negative to positive

transition.

0 is represented by positive to negativetransition.


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Differential ManchesterDifferential Manchester


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Differential ManchesterDifferential Manchester

Inversion at the middle of the bit intervalis used for synchronization, but thepresence or absence of an additional

transition at the beginning of the intervalis used to identify the bit.

It requires two signal changes to representto binary 0 but only one to represent

binary 1


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Bipolar EncodingBipolar Encoding

Like RZ, it uses three voltage levels: Positive

Negative

Zero Unlike RZ, zero level is used to represent

binary 0

Binary 1s are represented by alternate

positive and negative voltages


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Bipolar EncodingBipolar Encoding


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Alternate Mark Inversion (AMI)Alternate Mark Inversion (AMI)

Simplest type of Bipolar Encoding

Mark Comes from Telegraphy (1)

Alternate Mark Inversion means Alternate1 Inversion


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Alternate Mark Inversion (AMI)Alternate Mark Inversion (AMI)


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dc-lec-13 (intro to encoding techniques)

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