1, Principle:
General model modulated signal:
To expand, there are:
Regroup:
also because:
and so:
I, Q is a polar coordinate system representation. Wherein, I is the in-phase (in-phase) carrier amplitude, Q is an orthogonal (quadrature-phase) carrier amplitude.
Spectrum inversion:
2, the modulation and spectrum shifting
Known signal spectrum:
Is multiplied by the modulated carrier is multiplied by its spectrum
Spectrum shifting and then multiplied by its spectrum