DIGITAL TO DIGITAL CONVERSION
Digital-to-digital
encoding is the representation of digital information by a digital signal.
When binary 1s and
0s generated by the computer are translated into a sequence of voltage pulses
that can be propagated over a wire, this process is known as digital-to-digital
encoding.
Three techniques
used for this conversion are as follows:
I.
Line Coding
II.
Block Coding
III.
Scrambling
I.
Line Coding
Used to convert
digital data to digital signals.
The sender side
encrypts digital data into digital signals, while the receiving side decodes
the digital signal to regenerate the digital data and prevent the overlapping
of pulses and distortions.
Some key features
of line coding schemes:
1.
Digital-to-Digital Conversion: Line coding
converts digital data (1s and 0s) into a digital signal suitable for
transmission over a communication channel.
2.
Synchronization: ensure that the receiver can
accurately interpret the transmitted signal.
3.
Spectral Efficiency: refers to the rate at which data
can be transmitted over a given bandwidth.
4.
Error Detection and Correction: provide a mechanism
for error detection and correction.
5.
DC Component and Baseline Wander: The DC component
refers to the average voltage level of the signal, while baseline wander refers
to the gradual shift of the baseline of the signal over time.
6.
Transmission Rate: the number of voltage levels used
for signal representation, the duration of each bit, and the presence of
overhead for synchronization or error correction.
Classification of
line coding scheme:-
Classified into
several categories based on their characteristics and signal representation:
1. Unipolar
Encoding:
2. Polar Encoding:
3. Bipolar
Encoding:
4. Multilevel
Encoding:
5. Manchester
Encoding:
6. Miller
Encoding:
7. Scrambling and
Block Coding:
----------------------------------------------
ADVANTAGES OF LINE CODING SCHEME
Some of the key
advantages:
1. Digital-to-Digital Conversion:
2. Efficient
Spectrum Utilization:
3. Noise Immunity:
4.
Synchronization:
5. Error Detection
and Correction:
6. DC Balance and
Baseline Wander Mitigation:
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DISADVANTAGES OF
LINE CODING SCHEME
Some of the key
disadvantages:
1. Signal Bandwidth Requirement
2. Clock
Synchronization:
3. Baseline
Wander:
4. Error
Propagation:
5. Complexity and
Overhead:
6. Limited
Immunity to Interference:
7. Limited
Distance and Attenuation:
USAGES OF LINE
CODING SCHEME
Some of the key
usages of line coding schemes in DCN:
1. Data Transmission:
2. Networking
Protocols:
3. Physical Layer
Encoding:
4. Bandwidth
Optimization:
5. Error Detection
and Correction:
6. Clock Recovery
and Synchronization:
7.
Interoperability and Compatibility:
8. Noise Immunity
and Signal Quality:
9. Long-Haul
Transmission:
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Unipolar Scheme
The Unipolar Scheme
was designed as a Non-Return-to-Zero(NRZ) scheme where positive
voltage defines bit 1 and zero voltage defines bit 0, the signal does not
return to zero in the middle of the bit.
Figure from the web resource
FEATURES OF
UNIPOLAR SCHEME
Key features of
the unipolar scheme:
1. Single Voltage Level:
2. Simple
Implementation:
3. Ease of
Interpretation:
4. Low Complexity:
5. Limited
Spectral Efficiency:
6. DC Component:
7. Voltage Level
Representation:
8. Application in
Low-Speed Systems:
9. Compatibility:
TYPES OF UNIPOLAR
SCHEME
Some common types
of unipolar schemes:
1. Non-Return-to-Zero (NRZ):
- In NRZ encoding, one voltage level
represents a binary 1, while another voltage level represents a binary 0.
2. Non-Return-to-Zero Inverted (NRZI):
- NRZI encoding represents a binary 1 as a
transition and a binary 0 as no transition.
3. Unipolar Return-to-Zero (URZ):
- In URZ encoding, one voltage level
represents a binary 1, while the absence of a signal (returning to zero
voltage) represents a binary 0.
4. Unipolar Manchester:
- Unipolar Manchester encoding combines
elements of NRZ and NRZI by using transitions to represent binary data.
5. Unipolar Delay Modulation (UDM):
- UDM encoding uses variations in signal
delay to represent binary data.
- A delay in the signal indicates a binary
1, while no delay (zero delay) indicates a binary 0.
ADVANTAGES OF
UNIPOLAR SCHEME
Key advantages of
unipolar schemes:
1. Simplicity:
2. Low Power
Consumption:
3. Compatibility:
4. Robustness to
Noise:
5. DC Balance:
6. Ease of
Interpretation:
7. Lower
Complexity:
Disadvantages Of the Unipolar Scheme
Some of the key
disadvantages of unipolar schemes:
1. Limited Signal Range:
2. Baseline
Wander:
3. Limited
Spectral Efficiency:
4. DC Component:
5. Clock
Synchronization:
6. Interference Susceptibility:
7. Compatibility
Issues:
USAGES OF UNIPOLAR
SCHEME
Some common usages
of unipolar schemes in DCN:
1. Low-Speed Data Transmission:
2. Legacy Systems:
3. Short-Distance
Communication:
4. Control and
Monitoring Systems:
5. Embedded
Systems:
6. Education and
Training:
7. Serial
Communication Protocols:
8. Low-Cost
Consumer Electronics:
======================================================
Polar
In polar encoding,
used to represent binary values- positive voltage is represented by bit 1 and
negative voltage is represented by bit 0.
Changes its
voltage level when a different bit is encountered.
If the line is idle, then there is no
transition. With each inversion, the receiver is able to synchronize the
timer’s start to the transmission’s real arrival.
By using two
voltage levels, an average voltage level is reduced, and the DC component
problem of the unipolar encoding scheme is alleviated.
The polar encoding has three types.
Figure from the web resource
FEATURES OF THE
POLAR ENCODING SCHEME
Polar encoding
schemes in Digital Communication Networks (DCN) use both positive and negative
voltage levels to represent binary digits (0s and 1s).
Key features of polar encoding schemes:
1. Positive and
Negative Voltage Levels:
2. Bipolar or
Alternate Mark Inversion (AMI): binary 0s are represented by a zero
voltage level or no change in voltage, while binary 1s are represented by
alternating positive and negative voltage levels.
3. Improved
Spectral Efficiency:
This allows for higher data transmission rates within a given bandwidth.
4. DC Balance: ensuring that the
average voltage level of the transmitted signal remains close to zero.
5. Reduced Power
Consumption:
consume less power compared to unipolar encoding schemes.
6. Robustness to
Interference:
better robustness to certain types of interference, such as common-mode noise,
compared to unipolar encoding schemes.
7. Clock Recovery: accurate clock
recovery at the receiver to decode the transmitted signal accurately.
8. Compatibility: various
transmission media and communication protocols, making them suitable for a wide
range of applications within DCN.
Types of the polar
encoding scheme
Some common types
of polar encoding schemes:
1. Alternate Mark
Inversion (AMI):
2. Pseudoternary
Encoding:
3. Bipolar with
Zero Substitution:
4. High-Density Bipolar
(HDB):
5. Modified AMI
(M-AMI):
6. AMI with
Scrambling:
==========================
Advantages of the
polar encoding scheme
Some of the key
advantages:
1. Improved
Spectral Efficiency:
2. DC Balance:
3. Robustness to
Interference:
4. Reduced Power
Consumption:
5. Clock Recovery
and Synchronization:
6. Compatibility:
7. Data Density:
8. Versatility:
=============================================
Drawbacks of the
polar encoding scheme in DCN
Some key drawbacks
of polar encoding schemes are:
1. Complexity:
2. Limited Voltage
Levels:
3. DC Offset:
4. Susceptibility
to Interference:
5. Clock Recovery
Challenges:
6. Compatibility
Issues:
7. Power
Consumption:
8. Complexity of
Error Detection and Correction:
=================================
Usages of the polar encoding scheme
Some common usages
of polar encoding schemes in DCN:
1. High-Speed Data Transmission:
2. Long-Haul
Communication:
3. Digital
Subscriber Line (DSL) Systems:
4.
Telecommunication Networks:
5. Fiber-Optic
Communication:
6. Ethernet
Networks:
========================================
NRZ
· NRZ stands for
non-return zero.
· Represented either
positive or negative.
The two most
common methods used in NRZ are:
A. NRZ-L:
In NRZ-L encoding,
the level of the signal depends on the type of the bit that it represents.
If a bit is 0 or 1, then their voltages will be positive and negative respectively.
A. NRZ-I:
Changes its
voltage level when bit 1 is encountered.
NRZ-I is an inversion of the voltage level that represents 1 bit.
Provides
synchronization as whenever a 1 bit is encountered, the signal changes.
---------------------------------
RZ (Return to Zero
(RZ)):
· Uses three
different voltage levels to represent binary values.
· Bit 1 is used to
represent positive voltage,
· Bit 0 is used to
represent negative voltage and
· Bit zero voltage
for none.
· During the second
half of each bit, this signal enters a resting state(zero).
The disadvantage of
RZ:
It performs two
signal changes to encode one bit that acquires more bandwidth.
--------------------------------
Biphase
In this encoding
scheme signal changes in the middle of the bit interval but does not return to zero.
Biphase encoding
is implemented in two different ways:
A.Figure from the web resource
Manchester
It changes the
signal in the middle of the bit interval but does not return to zero for
synchronization.
In Manchester
encoding, a negative-to-positive transition represents binary 1, and a positive-to-negative transition represents 0.
B.
Differential Manchester
It changes the
signal at the middle of the bit interval for synchronization, but the presence
or absence of the transition at the beginning of the interval determines the
bit.
A transition means
binary 0 and no transition means binary 1.
In Differential
Manchester, the inversion at the middle of the bit is used.
-------------------------------------------------
Bipolar Encoding
The bipolar encoding
scheme represents three voltage levels: positive, negative, and zero.
In the Bipolar
encoding scheme, the zero level represents binary 0, and binary 1 is represented by
alternating positive and negative voltages.
Bipolar can be
classified as:
A.
AMI :
AMI stands
for alternate mark inversion where mark work comes from telegraphy
which means 1. So, it can be redefined as an alternate 1 inversion.
B.
B8ZS
B8ZS stands
for Bipolar 8-Zero Substitution.
This technique is
adopted in North America to provide synchronization of a long sequence of 0s
bits.
In most cases, the functionality of B8ZS is similar to the bipolar AMI, but the only
difference is that it provides synchronization when a long sequence of 0s
bits occurs.
C.
HDB3
HDB3 stands
for High-Density Bipolar 3.
HDB3 technique was
first adopted in Europe and Japan.
HDB3 technique is
designed to provide the synchronization of a long sequence of 0s bits.
Pseudo ternary
Three
different versions of this scheme are:
2B1Q
8B6T
4D-PAM5
Advantage:
DC component is
zero.
The sequence of 1s
bits is synchronized.
Disadvantage:
This encoding
scheme does not ensure the synchronization of a long string of 0s bits.
4. Multilevel
Scheme
The Multilevel
Coding scheme is also known as mBnL;
where:
m indicates
the length of the Binary pattern.
B denotes the
binary data
n indicates
the length of the signal pattern
L indicates
the number of levels in the signaling.
5. Multi
Transition(MLT-3)
This technique
uses three levels(+V,0,-V) and it also uses more than three transition rules in
order to move between the levels.
Rules are:
If the next bit is
0, then there is no transition.
If the next bit is
1 and the current level is not 0, then the next level will be 0.
If the next bit is
1 and also the current level is 0, then the next level is the opposite of the
last non-zero level.
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I.
Block Coding
The main problem
with line coding is Redundancy.
The Block Codes
mainly operate on a block of bits.
They make use of
the preset algorithm, take the group of bits, and then add a coded part to
them in order to make them a large block.
This large block
is then checked by the receiver after that receiver makes the decision about
the validity of the received sequence.
-------------------------------------------
II.
Scrambling
We can modify the
line and block coding by including scrambling.
Mainly the system
needs to insert the required pulses on the basis of the scrambling rules.
Given below are
the two common techniques used for scrambling:
B8ZS(Bipolar with
8-zero substitution)
With this technique, eight consecutive zero-level voltages are replaced by the sequence
of 000VB0VB.
In this sequence V mainly denotes violation and this is basically a nonzero
voltage that breaks the AMI rule of encoding.
The B in the given sequence denotes Bipolar which simply means nonzero voltage
level according to the AMI rule.
HDB3(High-Density
Bipolar 3-zero)
This technique is more conservative than B8ZS and in this four consecutive
zero-level voltages are replaced with a sequence of 000V or B00V. The main
reason for two different substitutions is just to maintain an even number of
nonzero pulses after each substitution.
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