Download - 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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Return to Zero (RZ)Return to Zero (RZ)
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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Return to Zero (RZ)Return to Zero (RZ)
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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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