how a base band signal is generated in ideal case and in prtactical case

thiis is anusha....sir would u plz tell me how a base band signal gets generated?
how it was calculated inn ideal case? and in practical?

one of two ways. An IF frequency carrier is modulated (Phase, Amplitude, or both) in some sort of I/Q modulator, and it is upconverted. The other way is that a single or dual DAC generates a modulated carrier, which is also upconverted.