Do we use IQ modulation because quadrature signals are a good physical implementation of phasors - or is it the other way around?
To elaborate a little:I'm having a hard time getting a clear explanation of we do things this way in radios. I can see that IQ signals and phasor representations go very well together. I understand that a pair of quadrature signals are needed to represent a rotating complex exponential as real values, and that modelling signals as complex exponentials is useful because when you multiply them, the phases add. It's all very elegant, but it doesn't fully explain why we do it this way. Why not make do with real functions for modelling, and use simpler mixers in the real world? I see 2 competing explanations:
We use complex exponentials because they're the simplest way to model a pair of quadrature signals from the real world. This raises the question of why we like quadrature signals in the real world in the first place.
We like quadrature signals in the real world primarily because that allows us to model things using complex exponentials.
Unfortunately no matter how hard I search and no matter how much I read, no source will commit to one of these explanations as the main reason for the whole thing. People tend to drop hints that it's a little bit of both, which is very unsatisfying. I'm not saying that it can't be partly both, but would one of these be enough on it's own? And if so, which one?
I know there is a real-world advantage to IQ modulation, in that it doesn't produce duplicate sidebands, so it's more efficient in terms of bandwidth. Is that it? Is that the fundamental motivation behind the whole thing?