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Advantages of NRZ line coding | Disadvantages of NRZ encoding

This page covers advantages and disadvantages of NRZ (Non Return to Zero) pulse shape in line coding. It mentions benefits or advantages of NRZ encoding and drawbacks or disadvantages of NRZ line coding.

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.

Polar NRZ-L and NRZ-I when zero is taken as 'Low' voltage Polar NRZ-L and NRZ-I when zero is taken as 'High' 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.

Unipolar NRZ

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]

Polar NRZ

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]

Bipolar NRZ

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.



Line coding techniques

Difference between Unipolar Polar and Bipolar coding    RZ vs NRZ vs Manchester coding    RZ vs NRZ pulse shapes    Advantages and disadvantages of NRZ encoding    RZ encoding    2B1Q coding    8B6T coding    4D PAM5 coding    MLT-3 coding    4B/5B encoding    8B/10B encoding    R8ZS scrambling    HDB3 scrambling   


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