Q and I seem to come up a lot in discussions of digital communications, such as the comprehensive answer provided to this question:
It seems like the Q and I channels ultimately are combined into a sin wave of a given frequency, phase and amplitude. If the communications system is all software (for example in a software-defined radio) is it necessary to worry about "Q" and "I"? Is this just an artifact of when receivers and transmitters were electronics based?
To make the question more concrete, the link provided talks about putting the even bits onto Q and the odd bits onto I. If this is the same thing as creating a sin wave of phase 0, 90, 180, or 270, then why bother with this seemingly unnecessary notation? Perhaps the pulse shaping (like an RRC filter) needs to be independently applied to the Q and I channels?