There's a whole host of radar research using OFDM/ Wifi (I wrote a paper on the topic a while back where i implemented it with some software defined radios).

The best paper on the topic is Martin Brauns[1]. It's insanely comprehensive and easy to digest.

[1] https://publikationen.bibliothek.kit.edu/1000038892/2987095

That sounds suspicious. Gait recognition is extremely difficult to do with any accuracy even with high resolution video in semi-controlled environments. Doing with with opportunistic 5G signals sounds far fetched.

There are proposals for the 6G standard to support Integrated Sensing and Communication(ISAC)[0]. So the hardware might natively be able to support gait recognition. The use cases given are UAV detection and localization. It sort of seems like this could bring Vernor Vinge's localizer mesh to reality, privacy implications be damned [0]https://www.ericsson.com/en/blog/2024/6/integrated-sensing-a...

I seem to recall reading (on HN, no less) that advanced passive radar technology is classified as munitions, by the US Government and is under export controls?

Hmm. I wonder how big a different the whole 24Ghz vs 6Ghz thing makes, when used as a radar.

To properly understand, how much resolution is needed for that ?

The 5G conspiracy theorists are paying attention.