Advantages of Polar line coding | Disadvantages of Polar signaling
This page covers advantages and disadvantages of Polar Line Coding and its basics. It mentions benefits or advantages of Polar Line Coding and drawbacks or disadvantages of Polar Line Coding.
Line coding is used to convert digital data into digital signal waveforms suitable to be transmitted. There are different line coding types based on pulse shapes used to map binary data. These types are unipolar, polar and bipolar.
What is Polar Line Coding?
Polar encoding uses two voltage levels. Binary 1 is represented by positive pulse (with voltage 'V') and binary 0 is represented by negative pulse (with voltage 'V'). Due to use of both levels, average voltage level on the line is reduced. Hence DC component issue observed in unipolar encoding is not there in polar coding type. There are various variants of polar encoding viz. NRZ (i.e. NRZ-L and NRZ-I), RZ, Biphase (Manchester, Differential Manchester).
As shown, polar NRZ uses positive pulse with 'V' amplitude to map binary '1' and negative pulse with 'V' amplitude to map binary '0'.
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.
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.
As shown, polar RZ encoding uses three voltage levels viz. 0, +ve and -ve. Signal state is decided by voltage level during first half bit period. Binary '1' is represented by positive voltage level and binary '0' is represented by negative voltage level during first half bit period. In the second half bit period pulse changes its voltage level. For binary '1' pulse voltage changes from +V to zero and remains there for rest of the half bit period. For binary '0' pulse voltage changes from -V to zero and remains there. Hence in polar-RZ coding type, waveform is not changing between bits but during each bit period.
Benefits or advantages of Polar Line Coding
Following are the benefits or advantages of Polar Line Coding:
➨It is easy to impelement line coding type.
➨Level voltage representation helps in reducing DC voltage.
➨NRZ-I helps in synchronization at the receiver due to use of transition to map binary '1'.
➨Polar RZ solves synchronization problem observed in polar NRZ type.
Drawbacks or disadvantages of Polar Line Coding
Following are the drawbacks or disadvantages of Polar Line Coding:
➨Long string of 1's and 0's create synchronization problem in polar NRZ. (This is solved by polar RZ type)
➨Baseline wandering issue persists in Polar NRZ.
➨Polar RZ requires two signal changes to encode bit and hence it occupies more bandwidth.
Line coding techniques
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