Modulation is a process that alters the characteristics of a carrier wave according to information in the message signal, m(t), to generate and transmit a modulated wave.

There are several types of modulation.

The unmodulated carrier is represented by the following equation: v(t) = Accos(2πfct + φ)

The amplitude-modulated carrier signal is represented by the following equation: v(t) = (m(t) + Ac)cos(2πfct + φ)

The frequency-modulated carrier signal is represented by the following equation: v(t) = Accos(2πfct + φ + ∫ m(t)dt)

The phase-modulated carrier signal is represented by the following equation: v(t) = Accos(2πfct + φ + m(t))

where

  • m(t) is the time varying message signal
  • A c is the amplitude of the carrier wave
  • f c is the frequency of the carrier wave