SIGNAL ENCODING

We can represent bits as digital electrical signals in many ways. Data bits can be coded into following two types of codes :

(a)               Non Return to Zero (NRZ Codes).

(b)               Return to Zero (RZ Codes)

NRZ Codes

In this type of codes, the signal level remains constant during a bit duration. There are 3 types of NRZ codes.

NRZ-L Coding

Bit is represented as a voltage level which remains constant during the bit duration.

NRZ-M Coding

A transition in the beginning of a bit interval whenever there is a 'Mark.

NRZ-S Coding

A transition in the beginning of a bit interval whenever there is a 'Space'. Let us see the following bit stream 10100110 into three different types of NRZ codes 

RZ Codes:

Following are the RZ Codes

(a)        Manchester Coding

(b)        Biphase-M Coding

(c)         Biphase-S Coding

(d)        Differential Manchester Coding.

Manchester Coding

There '1' is represented as the clock pulse itself and '0' as inverted clock pulse. It is widely used in local area networks. Fig.21 shows representation of '1' and '0'.

Bi-phase M Coding

  There is always a transition in the beginning of a bit interval and binary '1' is having additional transition in the middle of the bit interval.

Bi-phase S Coding

There is a transition at the beginning of a bit interval and binary '0' is having additional transition in the middle of the bit interval.

Differential Manchester Coding

There is always a transition in the middle of the bit interval and Binary '0' has additional transition in the beginning of the bit interval. Let us see Fig.22 in which bit sequence 10100110 has been shown in different RZ codes.