Bluetooth 5.1 Angle Of Arrival Backward Compatibility

I am currently designing a simple indoor location project to evaluate possibilities of Bluetooth 5.1 standard. The feature I would like to use is AoA (Angle of Arrival) introduced

Solution 1:

The implementation uses an extended version of the advertisement data that contains a "Constant Tone Extension". Both devices need to support this feature in order to calculate the angle. So no you can not use old 4.x devices. Both devices must explicitly support this feature, and use it. Keep in mind that far from all Bluetooth 5.1 and 5.2 devices support this feature.