Espressif has a new dual-band chip that does 2.4ghz and 5ghz wifi. That isn't the subject of this article, but ESP32 is gaining some new wifi capabilities.
I'm currently experimenting with ESP32-C5 engineering samples provided by Espressif, so hopefully some future ESPARGOS revision will be 5GHz-capable :)
But yeah, as far as I can tell, the chip can only extract CSI from WiFi (unless there is some hidden raw I/Q sample debug mode or something).
This project is amazing! I know there's some prior art, but I feel like I've never seen anything wifi-related moving so... smoothly? (With that high of an update/sample rate, I guess?) as your visualizations do.
I do have one question that wasn't quite clear to me, in case you happen to see this. There's a bunch of mentions of Channel State Information, but Google doesn't give a ton of info on it. So I'm just wondering, is CSI a "client-side" thing provided by the ESP32 for any Wi-Fi connection, or is it some special protocol feature that the AP or client have to enable?
Most wireless standards transmit some kind of pilot sequence next to the payload. A pilot is a sequence that is well-known to both TX and RX, and which allows the receiver to estimate the effect that the propagation has on the signal. The channel estimate is then used for equalization, i.e. undoing the channel effect.
For WiFi, some of the pilot symbols are called L-LTF (802.11g+n) and HT-LTF (802.11n). Every packet contains them as they are needed for successful communication. The ESP32 can provide channel estimates based on L-LTF and HT-LTF for any packet it receives. No need to enable anything, you can get CSI from every packet.
