I'm a bit of a noob here, looking for a simple formula or just a table which can tell me the absolute minimum phase shift angle possible for different variations of QAM. Particularly QAM 16, 64, 256 and 1024. If the answer is zero (is it?), then what is the minimum phase shift possible in each case other than 0?
Additionally, what is the limiting factor which governs the rate at QAM can switch between different phases? In other words, what is the maximum rate at which QAM can switch between different phases, and how is that determined for a particular device? Is there a relation to frequency of transmission (say a 1 GHz signal), or are frequency of transmission and phase-switching rate completely independent?