This is pretty important for modulation in digital communications. Interesting to see others than 2^N, and that 2^N are not square constellations, except for Q

This is pretty important for modulation in digital communications. Interesting to see others than 2^N, and that 2^N are not square constellations, except for QPSK. Sometimes minimizing amplitude (envelope) variations is more important, or sometimes susceptibility to white noise or phase noise. I remember learning about N-dimensional sphere packing for coding.