Designing a Modulator for a digital communication signal

If I have a device and its hardware that is a low-power and that the instantaneous energy it uses must be constant and my specifications indicate that the modulator must be rate adaptive. what modulation technique should I use, PAM modulation, QAM modulation, Phase modulation or multi-dimensional modulation?

I think my question here is what’s the relation of PAM, QAM, Phase modulation and multi-dimensional modulation with rate, power and energy.