6.2 CATEGORIES OF ENCODING SCHEMES

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6.2 CATEGORIES OF ENCODING SCHEMES

Encoding schemes can be divided into the following categories:

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  Unipolar encoding

  
  


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  Polar encoding

  
  


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  Bipolar encoding

  
  

Unipolar encoding: In the unipolar encoding scheme, only one voltage level is used. Binary 1 is represented by positive voltage and binary 0 by an idle line. Because the signal will have a DC component, this scheme cannot be used if the transmission medium is radio. This encoding scheme does not work well in noisy conditions.

Polar encoding: In polar encoding, two voltage levels are used: a positive voltage level and a negative voltage level. NRZ-I, NRZ-L, and Manchester encoding schemes, which we discuss in the following sections, are examples of this encoding scheme.

Bipolar encoding: In bipolar encoding, three levels are used: a positive voltage, a negative voltage, and 0 voltage. AMI and HDB3 encoding schemes are examples of this encoding scheme.

The encoding schemes are divided into three categories: (a) unipolar encoding; (b) polar encoding; and (c) bipolar encoding. In unipolar encoding, only one voltage level is used. In polar encoding, two voltage levels are used. In bipolar encoding, three voltage levels are used. Both polar encoding and bipolar encoding schemes are used in practical communication systems.

Note

The encoding scheme to be used in a particular communication system is generally standardized. You need to follow these standards when designing your system to achieve interoperability with the systems designed by other manufacturers.