Introduction :
There are two types of signals viz. analog and digital. There are four possible encoding techniques that can be used on the data. They are digital to digital, digital to analog, analog to analog and analog to digital.

Binary signals generated by computer (i.e. DTE) have two parameters viz. amplitude and duration. Encoding of digital data into digital signal is carried out by different ways viz. unipolar, polar and bipolar. These are known as line coding techniques.

## What is Unipolar Line Coding?

Introduction:
It is simple and most primitive type of encoding. Unipolar encoding encodes binary data in the form of 1's and 0's into digital pulses.

As shown binary zero is represented by one voltage level and binary one by another voltage level. Unipolar signaling uses only one polarity and only one of the two binary states is encoded usually binary '1'.

As shown, in this type, binary one is encoded as presence of pulse and binary zero by absence of pulse. Hence it is called "ON-OFF Keying". Unipolar signaling is categorized into NRZ and RZ based on pulse shapes.

Unipolar NRZ

As shown, Unipolar NRZ uses pulse with 'V' amplitude to map binary '1' and no pulse to map binary '0'.

Unipolar RZ

As shown, unipolar RZ uses pulse with high to low transition to map binary '1' and no pulse to map binary '0'. As shown, to map binary one, initially pulse remains high in the first half bit period and returns to zero in the next half bit duration. Pulse returns to zero in the middle of the bit period.

## Benefits or advantages of Unipolar Line Coding

Following are the benefits or advantages of Unipolar Line Coding:
➨It is simple encoding technique.
➨Unipolar NRZ : It requires less bandwidth for transmission.
➨Unipolar RZ : The spectral line present at the symbol rate can be used as clock signal.

## Drawbacks or disadvantages of Unipolar Line Coding

Following are the drawbacks or disadvantages of Unipolar Line Coding:
➨Average amplitude of unipolar encoded signal is nonzero. This creates DC component which shifts zero level of the signal which can not travel through some medium such as microwave.
➨Unipolar encoding leads to synchronization issue at the receiver when long string of ones and zeros are present in the binary data. This is because such data do not produce any transitions which may create problems in error detection and recovery.
➨It does not have any error handling technique (i.e. Error correction) .
➨It suffers from "Signal Droop" issue due to presence of low frequency components.
➨Unipolar RZ consumes twice bandwidth than unipolar NRZ.