Furthermore, CPM is typically implemented as a constant-envelope waveform, i.e., the transmitted carrier power is constant.
Minimum-shift keying (MSK) is another name for CPM with an excess bandwidth of 1/2 and a linear phase trajectory.
The raised cosine filter has zero crossings offset by exactly one symbol time, and so it can yield a full-response CPM waveform that prevents intersymbol interference (ISI).
Whenever the amount of ISI is known, such as with any partial-response signaling scheme, MLSE can be used to determine the exact symbol sequence (in the absence of noise).
One extremely popular form of partial-response CPM is GMSK, which is used by GSM in most of the world's 2nd generation cell phones.
In general, a standard FSK signal does not have continuous phase, as the modulated waveform cuts instantaneously between two sinusoids with different frequencies.