This project aims to send camera frames from an ESP32-CAM to a laptop over a distance of potentially several kilometers, using no additional hardware on the ESP32 end. How do we achieve this? As it turns out, WiFi radio waves can actually make it a very long way if there's nothing in the way. So if you just have a powerful receiving antenna, this should be possible.
The issue is, the standard IEEE 802.11 protocol (and by extension WiFi) doesn't support this sort of unidirectional communication. Usually, the receiver needs to send back and acknowledgement frames.
However, in the same way that your router sends out unidirectional data in the form of SSID broadcasts, so can we... if we're willing to use a somewhat unofficial function in the ESP32's API.
The idea behind this, and the code to do so, came from a video and repository published by @Jeija. At this stage, it doesn't work anywhere near as well as his. Still working out why that is, I've got a bit to learn here.
This software broadcasts the ESP32-CAM's camera framebuffer as a JPEG (JFIF) buffer. This is achieved by capturing the framebuffer of the camera, splitting it up into several packets, manually assembling IEEE 802.11 beacon frames in main.c, with each camera frame packet, and finally broadcasting them via the currently unofficial esp_wifi_80211_tx API in Espressif's esp32-wifi-lib.
As far as I know, you need a WiFi card that supports monitor mode on the receiving end, in order to sniff these packets. Once in monitor mode, we can receive the frames using receive.py, which will reassemble the packets and save it as a JPG file.
This project uses the Espressif IoT Development Framework. I used PlatformIO to upload and monitor the code.
To setup the receiving end, you will need python3-imaging installed, and a wireless adaptor that supports monitor mode (I used an Alfa AWUS036NHA).
You'll need to put your card in monitor mode, and adjust wlan1mon in receive.py to be your relevant interface name.
The code to do this is pretty simple, it just does a live scan of beacon frames, filters by MAC address (which is software-defined in main.c) and then tries to reassemble the frames, and if successful, saves it as test.jpg.