offset-QPSK could have constant evelope if not pulse-shaped.
In Lap's book ,about O-QPSK, to explain why use offset , he says when the constellation variation is pi, the evelope may go across zero , and at that time the signal is small which would be hard to amplify linearly, then spectrum regrows, which contributes to ISI and degrades BER.
Very often, should we consider that small constellation variation is better?
That's my own comprehension. Is it right ?