How to detect the relative direction of two mobile devices?

Question

How to detect the relative direction of two mobile devices?

When a mobile device (i.e. a modern smartphone) is taken near to a second mobile device, it is possible to detect inter-device proximity distance using proximity sensors, UWB or even NFC and so on. Now, how to detect the directions of the first mobile device relative to the second mobile device? I mean, how to detect which of the directions among left, right, up, down, front & back the first device is located of the second device? Any paper work reference would be appreciated.

Answer 1

This problem can't easily be solved without being able to install software on both devices. Devices usually have screen on front, and camera on front and back. So if you were to use screen to show a QR code, and both cameras on other device to look for that QR code, you'd be able to determinate relative position (based on angle and size of QR code seen on camera). You can use screen on both devices and all 4 cameras to cover almost all positions. This can also be improved by using compass and acceleration data. Another solution would be to take photos with both cameras on both devices at the same time, and look for repeated patterns in pictures (positioning based on idea that environment is constant and shared). Also, sound can be used to determinate distance if environment is fairly quiet.

BTW. If you can change hardware on both devices then solution would be quite simple to implement with directed IR transmitters and IR receivers on all sides.

Answer 2

Direction detection is one of the selling points for UWB (Ultra Wide Band) and Bluetooth 5.0 when combined with multiple antenna arrays.

This allows for AoA (Angle Of Arrival) to be calculated which will give you a relative direction to another device.

But given the form factor of the a phone it only really allows for the antenna separation in a single plan which means angle direction is similarly constrained (left/right, not up/down).