Line Coding

Line Coding

Line coding a technique to convert digital data into a digital signal.

In our last video Pulse Code Modulation, we learn that how to convert any analog signal into digital bits.Now if we want to send these bit over a media, then we need to convert these digital bits into a digital signal.This process is called line coding.In OSI layer video, we learn that it is done by the physical layer.



Important Definitions

We need some basic concepts to understand the Line coding process

Data Element.

A data element is the smallest piece of information that we want to send. It is bit 0 or 1)

Signal Element.

A signal element is the shortest element of the signal.

DE is the person and SE is the carrier

Data rate/Bitrate.

Data elements send in one second. The unit is bit/sec.

Signal rate/Baud rate.

Signal elements send in one second.The unit is baud.It is also known pulse rate, baud rate or modulation rate.

DC Component

It is due to the series of the same bit pattern(continuous 000000000000 or continuous 111111111111).I will result in the very low-frequency component.DC component is difficult to handle in coupling circuits.


Synchronization is a big concern in data communication.Clock pulse synchronization must match on both sides (Tx and Rx).Its mismatching can generate wrong data at the receiver side.

For a good digital transmission, clock frequency must be same on both sides (Tx and Rx).A good line coding technique tells the receiver beginning, mid and end of the pulse.


It has only one polarity waveform


It has two polarity waveform (+ve and -ve)


It has three level voltage waveform (+ve, 0V and -ve)

Non-Return to Zero NRZ

NRZ waveform only traces the +ve and -ve peaks.

It has two further classes

In NRZ-L, the voltage levels tell the bit information.

In NRZ-I,  The change in pattern tells the bit information.

Return to Zero RZ

RZ waveform trace 03 voltage levels +ve, 0 and -ve.

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