RADIO implements the Angle of Arrival (AoA) and Angle of Departure (AoD) Bluetooth Low Energy feature, which can be used to determine the direction of a peer device. The feature is available for the Bluetooth Low Energy 1 and 2 Mbps modes.
When using this feature, the transmitter sends a packet with a constant tone extension (CTE) appended to the packet, after the CRC. During the CTE, the receiver can take IQ samples of the incoming signal.
An antenna array is employed at the transmitter (AoD) or at the receiver (AoA). The AoD transmitter, or AoA receiver, switches between the antennas, in order to collect IQ samples from the different antenna pairs. The IQ samples can be used to calculate the relative path lengths between the antenna pairs, which can be used to estimate the direction of the transmitter.