[esrh]

I'd suggest reading https://dl.acm.org/doi/abs/10.1145/3310194 (2019) for a survey on early methods and https://arxiv.org/abs/2503.08008.

As for low level:

The most common early hardware was afaik esp32s & https://stevenmhernandez.github.io/ESP32-CSI-Tool/, and also old intel NICs & https://dhalperi.github.io/linux-80211n-csitool/.

Now many people use https://ps.zpj.io/ which supports some hardware including SDRs, but I must discourage using it, especially for research, as it's not free software and has a restrictive license. I used https://feitcsi.kuskosoft.com/ which uses a slightly modified iwlwifi driver, since iwlwifi needs to compute CSI anyway. There are free software alternatives for SDR CSI extraction as well; it's not hard to build an OFDM chain with GNUradio and extract CSI, although this might require a slightly more in-depth understanding of how wifi works.