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:



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:




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:



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:


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 


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:



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.



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:



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:



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 


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 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.

 Advantages of Polar NRZ

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).

Figure from the web resource 

The disadvantage of RZ:

It performs two signal changes to encode one bit that acquires more bandwidth.




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 


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:






DC component is zero.

The sequence of 1s bits is synchronized.



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;


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.


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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