In this manual, I present the basic principles that underlie the analysis and design of digital communication system. The digital communication involves the transmission of data in digital (0,1) form from a source that generates the information to one or more destinations. Particular importance in the analysis and design of communication system are the characteristics of physical channel through the information is transmitted .The characteristics of channel generally affect the design of the basic building blocks of the communication system. Below, we describe the modulation technique of a communication system and their system.