This ESP32 Antenna Array Can See WiFi

Summary

This video demonstrates how an ESP32 antenna array can visualize WiFi signals in real-time, showcasing how it captures the paths of radio waves, including reflections from metallic surfaces and non-metallic walls. The system uses synchronized ESP32 microcontrollers to achieve phase coherence, enabling precise measurements and WiFi camera images. The video also covers advanced topics like tracking passive targets, achieving depth perception outdoors, and exploring neural network-based localization techniques for both line-of-sight and non-line-of-sight environments. The demonstration emphasizes the potential for WiFi-based indoor navigation and localization systems.

Takeaways

• 😀 The ESP32 antenna array can visualize Wi-Fi signals, showing how they propagate and interact with various surfaces.
• 😀 Metallic surfaces act like mirrors for radio signals, causing reflections that can be visualized as delayed, colored paths in the Wi-Fi image.
• 😀 The ESP32 antenna array can track and visualize both direct and reflected paths of Wi-Fi signals.
• 😀 Highly directional antennas, like the Yagi antenna, focus Wi-Fi signals into narrow beams, resulting in overexposed images when pointed directly at the ESP32 array.
• 😀 Non-metallic surfaces only attenuate the signal, allowing devices to remain visible on the camera image even behind walls.
• 😀 The ESP32 uses phase coherence to synchronize its internal receivers, enabling accurate measurement of signal arrival angles.
• 😀 Phase uncertainty caused by imperfect internal clocks in ESP32s is corrected by providing a shared frequency reference and phase packets.
• 😀 The system uses Fourier transforms on channel state information to generate Wi-Fi camera images and estimate the angle of arrival of signals.
• 😀 Multiple ESP32 arrays can be combined for indoor localization, using triangulation or time/phase difference of arrival (TDoA) for higher accuracy.
• 😀 Neural networks and Channel Charting can enable localization even in non-line-of-sight scenarios by learning the environment's geometry from signal reflections.

Q & A

What does the ESP32 antenna array do with WiFi signals?

The ESP32 antenna array can visualize WiFi signals by detecting the emitted signal from a device like a smartphone, and it generates an image of the signal's propagation, allowing for insights into the device's location and the signal's path.

How does the ESP32 antenna array detect and visualize WiFi signals?

The ESP32 antenna array uses its sensors to capture the WiFi signal emitted by devices, then overlays that data over a camera image, showing signal propagation paths, delays, and interactions with reflective surfaces like walls.

What role do metallic walls play in WiFi signal propagation?

Metallic walls act as mirrors for radio signals, reflecting the WiFi signal. The ESP32 antenna array can detect both the direct path and the reflected path, with the reflected path showing a slight delay, indicated by a yellow-ish tint.

What does the yellow tint in the reflected path indicate?

The yellow tint represents a delay in the signal's reflection. The reflected signal takes longer to reach the antenna array than the direct line-of-sight signal, which causes the delay to be visualized with color.

How does the ESP32 antenna array react when the direct line-of-sight path is blocked?

When the direct line-of-sight path is blocked or attenuated, the array focuses on the reflected path, allowing it to still visualize the signal even when direct contact is obstructed.

How do non-metallic walls affect WiFi signals in this system?

Non-metallic walls only attenuate the WiFi signal, meaning devices can still be visible through the camera image even if the signal strength is reduced. The array can still track the signal behind these walls, unlike with metallic walls.

What happens when a highly directional antenna, like a Yagi antenna, is pointed at the ESP32 antenna array?

When a highly directional antenna, such as a Yagi antenna, is pointed directly at the ESP32 antenna array, the webcam image becomes overexposed due to the intense concentration of the signal in a narrow beam.

What is the effect of a reflector, like a metal wall, on the signal from a Yagi antenna?

When the Yagi antenna signal is directed at a metal wall, the signal is reflected, and the ESP32 antenna array can detect this reflected signal, showing a yellow-ish tint due to the increased path delay.

How can the ESP32 antenna array act as a passive radar system?

The ESP32 antenna array can track passive targets by detecting reflected WiFi signals from existing WiFi sources, such as SSID broadcasts from access points, effectively working as a passive radar system.

What is phase coherence, and why is it important for this system?

Phase coherence ensures that the signals received by multiple ESP32 chips are synchronized in both frequency and phase. This synchronization is crucial for accurately measuring the angle of arrival of signals and for generating precise WiFi camera images.