Modulation is a process where parameters of high frequency carriers can be changes with respect to instantaneous value of message signal.
there are three types of modulations:
1. according to message signal:
analogmodulation and digital modulation
2. according to form of carriers:
angle modulation and linear modulation
angle modulation is further divided into
frequency modulation and phase modulation
3. according to pulse
cotinous wave and pulse modulation.
continous wave are analog and digital whereas pulse modulation are PAM,PWM,PPM