# 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

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.

### Unipolar

It has only one polarity waveform

### Polar

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

### Bipolar

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

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.