SIGNALS:

AN electronic or a  light waves use to transmit data from one location to another location 

is called signal.

    EXAMPLE:  

                    generally we sent a  message from over friend. this is possible due to signals. 

COMPOSITE SIGNALS:

                                    composite signals is defined as two or more signals combine together to make 

a complicated signals is called a composite signals.

there a two types of composite signals. periodic signals and non periodic signals.

PERIODIC SIGNALS:

periodic signals are composite signals, in periodic signals two or more signals combine together to make a complicated signals, and in periodic signals their amplitude is not same with each other. 

NON PERIODIC SIGNALS:

          in non periodic signals two or more signals make a complicated signals  but their amplitude is same . this is called NON- PERIODIC  signals.

NRZ consist of unipolar, polar, bipolar, multilevel, multiple level.