A signal transmitted by a Bluetooth® Low Energy device has a frequency of approximately 2440 MHz, depending on the channel at a given transmission, resulting in a wavelength of approximately 12 cm in vacuum.
Usually Bluetooth LE devices are placed farther apart than this, meaning the signal undergoes multiple wave cycles as it propagates from the transmitter to the receiver. By measuring the phase difference of the signal as received by different antennas, the Angle of Arrival (AoA) receiver can determine the direction from which the signal is received. This is done with simple trigonometry, the phase difference yields a difference in travel time for the signal, and thus distance travelled.
The angle can be calculated using the following equation.
| Variable | Description |
|---|---|
| λ | The wavelength of the CTE signal. |
| ψ | The phase difference between the antennnas. |
| d | The distance between the antennas. |
The same principle applies to an Angle of Departure (AoD) system. The only difference is that the transmitter is switching antennnas while adjusting the phase to cause constructive interference in the desired direction, and destructive interference in other directions.
