There are 3 main types of digital pulse modulation:

1. Pulse time modulation (PTM), somewhat similar to analog phase modulation.
2. Pulse width modulation (PWM), the width of the pulse represents the signal.
3. Pulse code modulation (PCM), serial transmission of binary bits forming numeric or character codes that represent the signal.

All of these can be modulated on an RF carrier using any of the standard modulation techniques: AM, FM, Phase Modulation, etc. One advantage with AM digital pulse modulation techniques over AM analog is that the carrier can be 100% modulated, which cannot be done with analog, thereby allowing significant reductions in transmitter power without loss of coverage range. Sometimes FM digital pulse modulation techniques are referred to as Frequency Shift Keying (FSK). A very complex method of combining Phase Modulation and AM to increase the bit density of digital pulse modulation on an RF carrier is called Quadrature Amplitude Modulation (QAM).