Editing Pulse-position modulation (section)

==Non-coherent detection==
One of the principal advantages of PPM is that it is an ''M''-ary modulation technique that can be implemented non-coherently, such that the receiver does not need to use a [[phase-locked loop]] (PLL) to track the phase of the carrier. This makes it a suitable candidate for optical communications systems, where coherent phase modulation and detection are difficult and extremely expensive. The only other common ''M''-ary non-coherent modulation technique is [[Multiple frequency-shift keying|''M''-ary frequency-shift keying]] (M-FSK), which is the frequency-domain dual to PPM.