MODULATION AND CLASSIFICATION

Modulation is the very important technique used in communication system. The purpose of modulation system is to deliver a message signal from an information source in recognizable form to a user destination. For this the transmitter modifies the message signal into a suitable for transmission over the channel. This modification is achieved by means of a precise called "modulation". The modulation involves varying some parameter of a carrier wave in accordance with the message signal. The carrier is the high frequency wave than the message signal. The receiver recreate the original signal from the modulated signal. The recreation is done by the process called "demodulation". It is the reverse process of modulation.


 Classification of Modulation

 
.In continuous modulation , a sinusoidal wave is the carrier.
 .AM- When the amplitude of the carrier wave is change in accordance with the message signal , it is called amplitude modulation.
 .FM- The instantaneous frequency of the the carrier is change in accordance with the amplitude of the message signal.
 .AM- The angle of the carrier is change in accordance with the carrier.
 .PM- The phase of the carrier is change in accordance with the amplitude of the message signal.
 .Angle Modulation- The angle of the carrier is change in accordance with the carrier. In pulse modulation , the carrier is the periodic sequence of rectangular pulses.
 .PAM-In which carrier signal is sampled at regular intervals and each the signal is made proportional to the amplitude of the amplitude of the message signal.
 .PWM- It is also called pulse duration modulation or pulse length modulation. In this the width of each pulse is made proportional to the amplitude of the signal at the instant.
 .PPM- The amplitude and width of the pulse is kept constant and the position of the each pulse is varied in accordacne with modulating signal.