Bandpass Modulation/Demodulation techniques

Bandpass Modulation or Passband Modulation refers to modulation of signal over a carrier frequency. In these techniques the signal to be transmitted is sent by modulating either one or more of the three properties of carrier wave. And accordingly they are classified into diffrent categories as

1. Amplitude Modulation - In this the amplitude of carrier wave is modulated by the message signal. It can be expressed mathematically as

$s(t)=Am(t)*cos(wt)$

here Am is the modulating signal and w is the angular frequency of carrier.

2. Angle Modulation - In this the angle of carrier wave is modulated by the message signal. This is further divided into two types:

s(t) = cos(wt + Φ(t))

a. Frequency Modulation b. Phase Modulation

In practical digital communication systems, phase modulation frequently combined with amplitude modulation is used over Frequency modulation, as they provide better performance.