How can I generate a waveform with different Bandwidth Parts (BWP) (5G-NR)?

Hello,

I am working in Signal Processing in 5G NR area. I understand that one keypoint of this technology is to use different Bandwidth Parts (BWP) depending on the application in order to be more efficient, in multiple senses. However, I do not understand how am I supposed to implement the IFFT/FFT (Inverse-/Fast Fourier Transform) of different BWP if they are placed in the resource grid at the same time slot. I am asking about this scenario, because a lot of people are mentioning the inclusion of BWP in 5G by showing an illustration where different BWP with different subcarrier spacings are placed one above the other.

Are they supposed to be transmitted at the same time? Or it is just a drawing in order to exemplify that in 5G there will be different subcarrier spacings, not necessarily sent at the same time?

In case that they are supposed to be sent at the same time, how I am supposed to perform it? Each BWP must have its individual IFFT/FFT and then sum the signals if they are in time domain, or filter it if they are in frequency/resource grid domain? Or both must have the same IFFT/FFT (which for me is quite a nonsense)?

Even though Matlab offers 5G NR Toolbox, my question is conceptual not in the applience of code, which Matlab already has published several tutorials.

Thank you,