Multiple ESP32 devices collecting CSI - seeking advice

[FCS0906]

Hello everyone,

I am conducting a Wi-Fi CSI experiment using ESP32-S3 boards and ESP-IDF v5.2.

My current setup is as follows:

1. One ESP32-S3 is configured as an access point.
2. A smartphone connects to the AP and continuously sends UDP packets at a 50 ms interval.
3. Another ESP32-S3 runs the passive receiver application from ESP32-CSI-Tool.
4. Both the AP and the passive ESP32 collect CSI generated by the smartphone's transmissions.
5. The passive ESP32 operates in promiscuous mode on Wi-Fi channel 6.

I am now planning to expand the experimental area. Since the corridor is relatively long, I am considering adding one or more ESP32-S3 passive receivers near the AP or at remote locations along the corridor.

I was advised to connect all ESP32 devices to the same computer so that data collection and timing could be managed centrally. However, this may not be practical when the experimental area becomes larger because of the USB cable length.

I have read that ESP32 devices can store CSI data locally on an SD card or transmit data through a serial interface. I would like to ask whether anyone has used multiple ESP32 devices to collect CSI simultaneously, and what architecture you would recommend.

My questions are:

1. If the USB cables are too long, is it recommended that each remote ESP32 store CSI data locally on an SD card?
2. If SD cards are used, how should multiple ESP32 devices record a common experiment start time and run ID?
3. Are the local timestamps generated by different ESP32 devices synchronized with each other?
4. Would a common UDP burst, a GPIO trigger, or another synchronization marker be recommended?
5. Are there any recommendations for combining or comparing CSI collected by multiple spatially separated ESP32 receivers?

The project references are:

ESP32-CSI-Tool:
https://github.com/StevenMHernandez/ESP32-CSI-Tool

Official Espressif ESP-CSI project:
https://github.com/espressif/esp-csi

Hardware and software:

- Board: ESP32-S3
- ESP-IDF: v5.2
- Wi-Fi channel: 6
- Passive receiver: ESP32-CSI-Tool passive project

Thank you for any suggestions or recommendations.