Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
MSK is the general term for having several levels of whatever is being modulated, amplitude, frequency, or phase.
MPSK is the more specific term for several phase states that can be gone to. They are generally a power of two 2, 4, and 8 being the most common. After 8 the states get so close together that the SNR required for a decent BER gets very high. The advantage of MPSK is that a nonlinear amplifier (which has high efficiency) can be used.