Contents

1 What is modulation?

• Is the action of change one of more of the characteristics of a signal (the carrier) as a function of the information that transport other signal ($s\left[n\right]$), usually called the modulating signal.
• The carrier is usually a sine waveform signal or pulse/impulse signal.

2 PCM (Pulse-Code Modulation)

• PCM is the digital version of PAM. Each pulse represents a $s\left[n\right]$ sample.
• An example.
• PCM is used in the signal digitalization and signal processing systems.

3 PDM (Pulse Density Modulation)

• In PDM, the number of impulses (each with a constant amplitude) per unit of time defines $s\left[n\right]$.
• An example.
• PDM is used in the Sony’s Super Audio CD (SACD) format under the name Direct Stream Digital and in the living beings.

4 PWM (Pulse Width Modulation)

• In PWM, the duration of the pulse defines $s\left[n\right]$.
• An example.
• PWM is used in the control of the power supplied to electrical devices.

5 ASK (Amplitude-Shift Keying)

• $s\left[n\right]$ controls the amplitude of the carrier (a sine) signal.
• An example.
• ASK is used in telecomuication systems.

6 FSK (Frequency-Shift Keying)

• $s\left[n\right]$ controls the frequency of the carrier signal.
• An example.
• FSK is used in telecomunication systems.

7 PSK (Phase-Shift Keying)

• $s\left[n\right]$ controls the phase of a periodic signal (the carrier) which usually is a sine.
• An example.
• PSK is used in telecomunication systems.

8 QAM (Quadrature Amplitude Modulation)

• Originally designed to modulate two signals at the same time (one in amplitude and other in phase, and adding both).
• In the case of only one modulating signal, two or more sample of $s\left[n\right]$ define the amplitude and the phase of only the carrier, producing the so called QAM constellation.
• An example, here.
• QAM is used in telecomunication systems (DVB, for example).