Manchester Encoding

Example of Manchester Encoding

In Manchester encoding (as specified by IEEE 802.3 standards for 10 Mbps), a logic zero is signaled by a transition from 1 to 0, and a logic one is indicated by a transition from 0 to 1. The signal always undergoes a transition, even if it does not always occur at the bit boundaries (the line dividing one bit from another). Be aware that the encoding will occasionally be inverted, with 0 appearing as a transition from 0 to 1. 

As an example, in Manchester Encoding the pattern of bits " 1 0 0 0 1 0 " encodes to " 01 10 10 10 10 01 01 10".

Encoding and Decoding

Encoding is described as the process of creating and converting a message or information into a coded format. Coding is a program that allows a certain piece of information to be in a format specified by certain protocols. Coding and system have no separation. Encoding is formed or structured by the encoder, who develops and places the message in such a way that the reader or receiver can understand it.

Decoding is defined as the understanding and interpretation of the encoded message. This process is carried out by a decoder, which is either a person or a system that transforms and reads the coded message. When the message is easily understood by the receiver, decoding is successful. As a result, the receiver can send a reply or another message to the sender.
When the message reaches the receiver, it should be in a clear, suitable, and meaningful format so that there is no misunderstanding regarding the message's aim and purpose. Decoding can be verbal or nonverbal, depending on the sort of communication sent by the encoder.

Representation of Bits

According to IEEE 802.3 standards, a logic one bit represents a transition from 0 to 1 (low to high) in the middle of the bit, while a logic zero bit represents a transition from 1 to 0 (high to low) in the middle itself. A transition always occurs in the signal, even if it does not always happen at the boundaries. 

A complete inverted convention is given by Dr. G.E Thomas. According to this convention, 0 displays the transition from 0 to 1, while 1 displays the transition from 1 to 0.

Non-Return-To-Zero [NRZ]

The voltage level of NRZ's code remains constant in a bit interval. It creates a problem at the receiver's end if the data is a long sequence of 1s and 0s, and that is why the binary data to be transmitted over the cable are not sent as NRZ. The major problem is improper synchronization due to a lack of transmissions.

The two types of NRZ are:-

1. NRZ level encoding: The first bit of data is considered for polarity change. The polarity changes when the incoming signal changes from 0 to 1 or 1 to 0.
    
2. NRZ-Differential/ Inverted encoding: The bit logic is zero if there is no transition at the beginning of the bit interval, while the bit logic is one if there is a transition at the beginning.

Unipolar Non-return-to-zero Level

Unipolar Non-return-to-zero Level (NRZ-L) is a digital encoding scheme where the presence of a signal represents one binary state (typically a high voltage level), while the absence of a signal represents the other binary state (typically a low voltage level). In NRZ-L, the signal remains at the same level throughout the bit duration, resulting in straightforward encoding and decoding processes. However, it is susceptible to baseline wander and synchronization issues.

Bipolar Non-return-to-zero Level 

Bipolar Non-return-to-zero Level (NRZ-L) is a variation of the NRZ-L encoding scheme where both positive and negative voltage levels represent binary states. Unlike unipolar NRZ-L, which uses only one voltage level to encode binary data, bipolar NRZ-L alternates between positive and negative voltage levels to represent binary ones and zeroes. This encoding scheme helps mitigate the problem of baseline wander by ensuring a balanced number of positive and negative voltage transitions.

Non-return-to-zero Inverted 

Non-return-to-zero Inverted (NRZI) is a digital encoding scheme where a transition (change in voltage level) represents a binary one, while the absence of a transition represents a binary zero. Unlike NRZ-L, where the signal level is maintained throughout the bit duration, NRZI relies on transitions to encode data. NRZI is particularly useful in mitigating the issue of long consecutive runs of zeroes present in NRZ-L encoding. However, it requires a clock signal for proper decoding and is sensitive to synchronization errors.

Characteristics of Manchester Encoding

1. Logic 0 denotes a 0 to 1 transition, while Logic 1 denotes a 1 to 0 transition.
    
2. A transition always happens at the center of each bit, but it does not always happen at the bit boundary.
    
3. For the conversion of binary digits to electrical signals, Differential Physical Layer Transmission does not use an inverting line driver, due to which the signal on the wire does not mismatch with the encoder’s output.
    
4. Zero is recorded for a low-to-high transition, while One is recorded for a high-to-low transition.
    
5. Every bit is sent at a defined rate.
    
6. Each bit is encoded by a positive or a negative phase transition, which is why Manchester Encoding is also called Biphase Code.
    
7. The transition, which is precisely used to note 1 or 0, happens at the halfway point of the period.
    
8. Manchester encoding requires twice the bandwidth as compared to the bandwidth needed to transmit the original signal.
    
9. The Digital Phase Locked Loop (DPLL) deallocates the timing and value of each bit and also extracts the clock signal.

Advantages of Manchester Encoding

Below are the advantages of Manchester encoding.

1. Easy Error Detection: Manchester encoding provides a method for finding the errors in the transmitted data. An error in a bit is indicated when there is a change in the voltage level during a time interval.
    
2. Easy to Implement: Manchester Encoding is a simple and easy-to-implement encoding scheme as compared to other encoding techniques.
    
3. Self-Clocking: The receiver can synchronize its clock with the transmitter, which ensures that the data is received and transmitted at the same rate.
    
4. No DC Component: It removes the DC component from the transmitted signal, thereby reducing the risk of errors due to external sources.

Disadvantages of Manchester Encoding

Below are the disadvantages of Manchester encoding.

1. High Bandwidth Requirement: Manchester encoding requires twice the bandwidth as compared to the bandwidth needed to transmit the original signal.
    
2. Low data rate: It takes more time to transmit the data in Manchester encoding as it has a low data rate as compared to NRZ encoding.
    
3. Synchronized Clock: The receiver's and the transmitter's clock is synced, even though it sometimes requires synchronization.

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Difference between Manchester and Differential Manchester Encoding

Frequently Asked Questions

What makes Manchester Encoding a synchronous encoding technique?

In Manchester Encoding, logic one corresponds to high while logic zero corresponds to low. It is called synchronous encoding because the lows and the highs are combined in one binary sequence or bitstream as they occur in the same amount of time.

What convention is given by Dr. G.E Thomas?

According to Dr. G.E Thomas, zero displays the transition from zero to one, while one displays the transition from one to zero.

What is the Manchester encoding scheme used for?

Manchester code, sometimes referred to as phase encoding, is a type of line code used in communications and data storage in which each data bit is encoded either high then low or low then high for an equal amount of time. The signal has no DC component and is self-clocking.

What is the difference between Manchester encoding and other encoding techniques?

Manchester encoding differs from other encoding techniques as each data bit length is already defined or predefined which is not the case with other encoding techniques. In Manchester encoding, the direction of transition represents the bit state.

Conclusion

In this article, we have discussed Manchester Encoding, which is a synchronous clock encoding technique. We have also seen the characteristics, advantages and disadvantages of the same. To learn more about ethernet in Computer Networks, you can refer to the below-mentioned article:

Ethernet in Computer Networks

Phases of Compiler

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