Kefei,
Unfortunately we do not have any examples of performing this type of processing in MATLAB. I would start by learning about FFTs and the role of window functions for the FFT. There is a lot of literature available on the internet on this topic using MATLAB as the programming language. MATLAB has several functions to assist in this type of processing.
Overlapped FFTs as described in Justin’s response are how Spike converts I/Q data into a series of closely spaced spectrums.
Regards,
Andrew