Full Form of CPM

What is CPM Full Form?

CPM full form is Continuous Phase Modulation.

What is Continuous Phase Modulation?

Continuous phase modulation (CPM) is a method for modulation of data commonly used in wireless modems. In contrast to other coherent digital phase modulation techniques where the carrier phase abruptly resets to zero at the start of every symbol (e.g. M-PSK), with CPM the carrier phase is modulated in a continuous manner. For instance, with QPSK the carrier instantaneously jumps from a sine to a cosine (i.e. a 90 degree phase shift) whenever one of the two message bits of the current symbol differs from the two message bits of the previous symbol. This discontinuity requires a relatively large percentage of the power to occur outside of the intended band (e.g., high fractional out-of-band power), leading to poor spectral efficiency. Furthermore, CPM is typically implemented as a constant-envelope waveform, i.e., the transmitted carrier power is constant. Therefore, CPM is attractive because the phase continuity yields high spectral efficiency, and the constant envelope yields excellent power efficiency. The primary drawback is the high implementation complexity required for an optimal receiver.

Continuous phase modulation (CPM) is a constant-amplitude modulation scheme that is a generalization of continuous phase frequency shift-keying (CPFSK) or minimum shift-keying (MSK). The lack of phase discontinuities reduces high-frequency spectral content, making CPM a highly spectrally efficient scheme.

One form of CPM that can result in significant coding gains is multi-h phase coding, where h stands for the modulation index. This scheme is a generalization of CPFSK schemes because different phase changes result from the transmission of the same symbol in two contiguous symbol intervals.