POLAR ENCODING

 POLAR ENCODING 

 Polar encoding uses two levels ( positive and negative) of amplitude.

The polar encoding is catagorise into 3 types :-

·         NRZ(non return to zero)

·         RZ(return to zero)

·         Biphase

    Non Return To Zero (NRZ)-

  In NRZ encoding , The level of the signal is always either positive of negative .

               The NRZ encoding includes two methods :-

·         Non Return To Zero ,Level (NRZ-L)

·         Non Return To Zero ,Invert (NRZ-I)

NRZ-L :-  

In NRZ-L encodingthe level of the signal depends on the type of bit it represents.

§  A positive voltage means the bit is 0 , and a negative voltage means the bit is 1 .

§  Thus the level of the signal is dependent upon the state of the bit.

NRZ-I  :-

In NRZ-I , on inversion of voltage level represents a 1 bit. A 0 bit is represented by no change .

NRZ-I is superior to NRZ-L due to the synchronization provided by signal change each time a 1 bit is encountered.

NOTE- In NRZ-I the signal is inverted if a binary 1 is encountered.

For Example – In NRZ-L , The binary 0s is represented by  positive voltage and binary 1s is represented by negative voltage.

In NRZ-I , The binary 0s is represented by no change & Binary 1 is represented by inversion of the voltage level.

Fig. showing NRZ-L & NRZ-I encoding

Return To Zero (RZ) –

 Return to zero encoding uses Three values :

§  positive

§  negative

§  zero

·         In RZ the signal changes not between bits but during each bits.

·         In  RZ the binary 0s is reprented by negative-to-zero and the binary 1s is represented by positive-to-zero.

Fig. showing RZ encoding

Biphase Encoding –

 The Biphase encoding is the best existing solution to the problem of synchronization.

            In this method , The signal changes at the middle of the bit intervel but doses not return to zero , Instead it continues to the opposite pole.

Biphase encoding is classified into 2 types :-

·         Manchester Encoding

·         Differential Menchester Encoding

Manchester Encoding :-

§  In Manchester encoding , The transition at the middle of the bit is used for both synchronization and bit reprentation.

§  In Manchester encoding , The binary 0s is represented by a positive-to-negative transition and The binary 1s is represented by negative-to-positive transition.

Fig. showing manchester encoding

Differential Manchester Encoding –

§  In Differential Manchester , The inversion at the middle of bit interval is used for synchronization.

§  A transition means Binary 0 & no transition means Binary 1.

§  Differential Manchester requires two signal changes to represent binary 0 , But only one to represent binary 1.

Fig. showing Differential manchester

Bipolar Encoding –

 Bipolar encoding uses three voltage levels :-

·         positive

·         negative

·         zero

§  In bipolar encoding the binary 0s is represented by zero level And Binary 1s is represented by alternating positive and negative voltage.

§  If the first 1 bit is represented by the positive amplitude , The second will be represented by the negative amplitude , The third by the positive amplitude & so on…

The bipolar encoding is classified into 3 types :-

·         AMI(Bipolar Alternate Mark Inversion)

·         B8ZS(Bipolar 8-Zero Substitution)

·         HBD-3(High Density Bipolar 3)

Bipolar Alternate Mark Inversion(AMI) –

§  Bipolar Alternate Mark Inversion (AMI) is the simplest type of bipolar encoding.

§  The AMI means alternate 1 inversion . In AMI encoding , The binary 0s is represented by neutral , zero voltage & Binary 1s is reprented by alternating positive and negative voltage.

Fig. showing Bipolar AMI Encoding