Line Coding

Line Coding

Digital Line Coding is a special coding system chosen to allow transmission to take place in a communications system. The chosen code or pattern of voltage used to represent binary digits on a transmission medium is called line encoding. The types of line encoding are polar, unipolar and bipolar.

Unipolar

-Uses only one voltage level-Named so beacause it only uses one polarity -assigned to one of the two binary states, usually the 1. -The other state, usually the 0, is represented by zero voltage. -Has dc component. -Lack of synchronization is an issue in unipolar encoding.

Polar

NRZ-L

NRZ-I

-The level of the signal is dependent upon the state of the bit-Positive voltage usually means the bit is 0-Negative voltage usually means the bit is 1

-The signal is inverted if a 1 is encountered -A 0 bit is represented by no change

NZ

A good encoded digital signal must contain a provision for synchronization

NRZ

the transition at the middle of the bit is used for both synchronization and bit representation

MANCHESTER

The bit representation is defined by the inversion or noninversion at the beginning of the bit. A transition means binary 0, and no transition means binary 1.

Differential Manchester

In bipolar encoding, we use three levels: positive, zero, and negative Zero level in bipolar encoding is used to represent binary 0. The 1s are represented by alternating positive and negative voltages. AMI = Alternate Mark Inversion

Bipolar