Converting IQ to RF data I appreciate any help: I wanna convert IQ data to its RF data, representing an image. The center frequency and sampling rate are available. What I do is:

First I do up-sampling in MATLAB by applying interpolation along depth. So, the new data has a new sampling frequency higher than the first one.

My questions are: 1) do I need to do low-pass filtering before multiplying the data by the exponential term (that converts IQ to RF)? 2) what is the exponential form that I need to use to multiply the IQ data by?

I was wondering if the length of one of my vectors is, say, 1000, ( Calling it vector A), then how to do zero padding? (I assume a number of zero elements are added to both start and end of this vector and then the Low-pass filtering is done) How to decide about the number of zeros added? Sorry, if these seem to be too simple questions

I've read the documentation I copy here and it is confusing for me: (Page 8 and afterwards)

http://folk.ntnu.no/htorp/Undervisning/TTK10/IQdemodulation.pdf

Thanks
For ideal performance, you can DFT your input, pad out the spectrum with zeros, and inverse DFT the result.  This is not a particularly efficient approach, though.

Pretty much the same result is obtained with interpolation by zero-padding and then running that stream through a low pass filter.  An FIR sinc filter is preferred for this for two reasons--(1) it has nearly ideal performance and introduces negligible distortion into the baseband signal, and (2) when zero padding, most of your input samples are zero.  Since 0*x=0, you don't have to do all those multiplies; for your 6:1 example, you can design a 72-point FIR and still only do 12 multiplies per output sample.

Once the filtering is done, you can upconvert (multiply by the exponential).  This should be $e^{j\omega t}$ where $\omega=2\pi f$ and f is your RF carrier frequency.