What's the difference between a spectrogram of the Doppler domain and the Doppler Spectral Density?
Started by 5 years ago●2 replies●latest reply 5 years ago●503 viewsHello colleagues,
Background: I've performed some measurements of Doppler shift in a mobile wireless channel with both transmitter (continuous wave) and receiver moving. In the spectrogram, I can clearly see specular and NLOS frequency components shifted due to the movement.
Quick question here:
I've been using interchangeably these terms:
Doppler Spectral Density
Spectrogram of the Doppler Domain
Doppler Profile
Doppler Channel Response
Are these terms the same thing?
Which phrase would you prefer? Why? Or In What Context?
ReachRF-
One comment I might make would be to be careful using the word "domain". To see Doppler shift you are transforming data from time to frequency domain ... I don't see in the literature a carefully defined "Doppler domain". For example the wikipedia page on "Pulse-Doppler signal processing" only mentions "domain" in context of time and frequency.
Spectrogram and spectrograph are two commonly used terms for viewing a series of frequency transforms over time, maybe if there is something "Doppler unique" about the frequency transforms you make to get that data, it might be a transformation into "the Doppler domain". I do see mention of "range Doppler domain" so maybe that's it, but in that case it looks like FFT plus a combination of windowing and filtering before, and mapping *after*, the transformation into the frequency domain.
I could easily be wrong on this, but does seem to jump out at first glance.
-Jeff
Jeff,
My sincere gratitude for your reply. Thoughtful, and insightful.
This is where I have struggled, too. In the literature, I first heard of "Doppler domain" from Skolnik, Introduction to Radar Systems (2nd Edition).
Where we can see that the origin is always 0Hz, and any increment (+/-) is the relative shift in carrier.
Yet, I have yet to see this used in other literature.
Your response has me leaning towards, "time-variant Doppler Spectral Density" (DSD), since I have seen that used recently in channel measurement literature (albeit circa 2009).
I have also come across, "Frequency-time Doppler profile" as recently as 2013, but that's a lot to write out each time, and FTDP looks weird.
So I'll stick with calling it: the time-variant DSD, even though the Density aspect doesn't really make sense to me since I'm using a sliding FFT (after removing carrier frequency offset). To me density makes more sense when computing probabilities.