Pulse Modulation

Pulse modulation (PM) offers two potential advantages over CW modulation

• The transmitted power can be concentrated into short bursts instead of being generated continuously. This enables the use of devices which operate better in pulse regime than in CW regime, mostly due to thermal reasons (e.g. semiconductor lasers ,microwave active devices)
• Time between pulses can be filled by sampled signal from other sources – a scheme termed time‐division multiplexing

Pulse Amplitude Modulation:

Pulse-amplitude modulation (PAM), is a form of signal modulation where the message information is encoded in the amplitude of a series of signal pulses. It is an analog pulse modulation scheme in which the amplitudes of a train of carrier pulses are varied according to the sample value of the message signal.

Exam111111ple: A two-bit modulator (PAM-4) will take two bits at a time and will map the signal amplitude to one of four possible levels, for example −3 volts, −1 volt, 1 volt, and 3 volts.

Demodulation is performed by detecting the amplitude level of the carrier at every symbol period.

Pulse Width Modulation:

Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a modulation technique that conforms the width of the pulse, formally the pulse duration, based on modulator signal information. Although this modulation technique can be used to encode information for transmission, its main use is to allow the control of the power supplied to electrical devices, especially to inertial loads such as motors.

The PWM switching frequency has to be much faster than what would affect the load, which is to say the device that uses the power. Typically switchings have to be done several times a minute in an electric stove,

The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time. Duty cycle is expressed in percent, 100% being fully on.

Pulse Position Modulation:

Pulse-position modulation (PPM) is a form of signal modulation in which M message bits are encoded by transmitting a single pulse in one of  possible time-shifts. This is repeated every T seconds, such that the transmitted bit rate is M/T bits per second. It is primarily useful for optical communications systems, where there tends to be little or no multipath interference.