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Introduction: Digital signal is sequence of discrete, discontinuous voltage pulses. It is used to map data bits by various encoding techniques such as NRZ, RZ, biphase etc.

### What is NRZ encoding ?

In this encoding technique, binary data are represented by voltage level of pulse signal. During entire bit period (Tb), voltage level remains constant. In NRZ coding, binary bit '1' is represented by high level voltage and binary bit '0' is represented by low level voltage.

There are two variants of NRZ encoding viz.NRZ-Level and NRZ-Inverted.
NRZ-L (NRZ-Level) : In this type, level of signal is dependent upon state of the bit. Positive voltage maps binary '1' and negative voltage maps binary '0' or viceversa. Hence in NRZ-Level encoding type, polarity of signal changes when incoming signal changes from 1 to 0 and from 0 to 1. NRZ-L is similar to NRZ except for first data bit. NRZ does not consider 1st data bit as polarity change where as NRZ-L encoding does consider.
NRZ-I (NRZ-Inverted) : In this type, inversion of voltage represent binary '1' and no change in voltage represent binary '0'. Here data is not represented by any level voltage but by transition between two polar voltages. Transition at the beginning of the bit interval is considered as binary '1' where as no transition is considered as binary '0' and viceversa. It is also called differential encoding. NRZ-I has advantage compare to NRZ-L.

As shown, using unipolar NRZ encoding, binary '1' is mapped using pulse of some amplitude 'V' for entire bit period and binary '0' is mapped by absence of pulse for entire bit period.
Example of Unipolar NRZ coding :
INPUT : [1 0 1 0 0 1 1 1 0]
OUTPUT : [+ve pulse, DC, +ve pulse, DC, DC, +ve pulse, +ve pulse, +ve pulse, DC]

As shown, using polar NRZ encoding, binary '1' is mapped using positive pulse of amplitude 'V' and binary '0' is mapped using negative pulse of amplitude 'V'.
Example of Polar NRZ coding :
INPUT : [1 0 1 0 0 1 1 1 0]
OUTPUT : [+ve pulse, -ve pulse, +ve pulse, -ve pulse, -ve pulse, +ve pulse, +ve pulse, +ve pulse, -ve pulse]

As shown, using Bipolar NRZ encoding, binary '1' is mapped using positive pulse and negative pulse of amplitude 'V' based on its alternate positions and binary '0' is mapped by absence of pulse.
Example of Bipolar NRZ coding :
INPUT : [1 0 1 0 0 1 1 1 0]
OUTPUT : [+ve pulse, DC, -ve pulse, DC, DC, +ve pulse, -ve pulse, +ve pulse, DC]

### Benefits or advantages of NRZ encoding

Following are the benefits or advantages of NRZ encoding:
➨It is simple line coding technique than RZ type as pulse does not return to zero while mapping binary data (1's and 0's).
➨For unipolar NRZ signaling less bandwidth is needed.
➨In polar NRZ and bipolar NRZ, no low frequency components are present in the signaling waveforms after mapping.

### Drawbacks or disadvantages of NRZ line coding

Following are the drawbacks or disadvantages of NRZ line coding:
➨Presence of low frequencies may cause droop in the signal waveforms.
➨No error correction is done.
➨Long string of ones and zeros lead to loss of synchronization between clocks of transmitter and receiver. Hence separate clock line is required between transmitter and receiver to eliminate this problem.
➨No clock is available.