I am a Software Engineer without much signal processing background and currently spending and experimenting to get use to it.
My scenario: Assume a speaker and a microphone array. A speaker emits an ultrasonic sound and the microphone records at the same time. From the signal recorded from the microphone array, I am subtracting the emitted signal which was 1) directly recorded and 2) recorded after reflected from stationary objects. The spectral subtraction should leave only the reflected signals from moving objects. Given the spectral information of the movements, by applying correlation algorithms, I plan to localize the movement.
What I have tried: Without subtracting, I am able to localize the movements. However, the movements are difficult to identify without knowing the direction of the movement as the sounds reflected from stationary objects are also getting localized at the same time.
Problem: I have recorded the reference signal when there were no movements and subtracted it from the signal which were recorded while movements were present. However, using correlation algorithms on subtraction results no longer provides location of the movement.
A little bit more details: Given the fft result refSig (reference signal) and tarSig (reference signal + reflected movement signal), assume that refSig is a+bi and tarSig is (c+di). To only leave movement, I did (a-c) + (b-d)i.
I got such subtraction idea from reading papers related to MTI filters (usually used for detecting fast moving object like airplanes).
How could I fix this or improve this?