# FSK combined with either ASK or PSK?

Why is it that we are able to combine Amplitude and Phase modulation (Resulting in QAM) but are not able to do so with frequency? Why not combine all three degrees of freedom (Amplitude, Frequency, Phase) for modulation?

• Frequency and phase are not independent degrees of freedom since $f=\dfrac{\mathrm{d}\phi}{\mathrm{d}t}$. – The Photon May 7 '15 at 16:52
• Somehow I'm guessing that adding FSK into the mix doesn't improve power or spectral efficiency, and therefore is pointless... That's just a guess--I could be grossly wrong. – Zulu May 7 '15 at 17:05