Pulse Position Modulation (PPM)

Pulse Position Modulation (PPM) is a type of modulation technique where the position of a pulse in a fixed time slot is varied to represent a digital signal. PPM is commonly used in digital communication systems to transmit information over a channel.

In PPM, a series of pulses are transmitted within a fixed time slot, with the position of each pulse within the slot corresponding to the value of the digital signal being transmitted. The duration of the pulse is fixed, while the time between successive pulses varies depending on the digital signal.

Pulse Position Modulation (PPM)

The basic block diagram of a PPM transmitter includes a pulse generator, a modulator, and a carrier signal generator. The pulse generator produces a series of pulses with a fixed duration. The modulator varies the position of the pulse within a fixed time slot according to the digital signal being transmitted. The carrier signal generator produces a carrier signal to carry the modulated signal.

The modulated signal can be expressed as:

s(t) = ∑ a_n p(t-nT-t_i)

where a_n is the amplitude of the nth pulse, p(t) is the pulse shape, T is the duration of the pulse, and t_i is the time position of the pulse within the fixed time slot.

PPM has several advantages over other modulation techniques, including high data transmission rates and low bandwidth requirements. However, PPM also has some limitations, including low noise immunity and high sensitivity to timing errors. To address these limitations, other modulation techniques such as Pulse Width Modulation (PWM) and Pulse Frequency Modulation (PFM) have been developed.