IQ to Direction Radiogoniometry

Bluetooth Angle of Arrival (AoA) direction finding, part of the Bluetooth 5.1 specification, improves the accuracy of locating using Bluetooth signals. AoA uses the phase difference of the received signal at multiple antennas in a Bluetooth-enabled device to calculate the angle of the incoming radio signal, which can then be used to pinpoint the direction from which the signal was sent.

IQ data comes into play as part of the signal processing. In radio systems, IQ data represents the peaks and troughs of a waveform. I is for ‘In-phase’ part which can be thought of as a signal’s cos component, while Q is for ‘Quadrature’ which is the sin component. This data is derived from the Radio Frequency (RF) front end of the receiver hardware.

The IQ data is translated into direction for further processing, such as determining signal direction in three-dimensional space. Algorithms such as MUSIC (Multiple Signal Classification), ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) and PDDA (Phase Difference Direction Algorithm) turn the IQ data into a pseudo-spectrum the peaks of which provide the direction.

PrecisionRTLS Location Engine Pseudo-spectrum

Radiogoniometry has many complexities such as multipath propagation where a radio signal reaches the receiver by two or more paths due to reflection or diffraction from structures or objects in the environment. This causes multiple peaks in the plot. This is where anti-interference algorithms come into play that can mitigate the effects of signal interference, such as multipath propagation and environmental noise. These algorithms rely on statistical signal processing techniques and adaptive filtering methods to distinguish between the desired signal and interference, thereby enhancing the accuracy of direction finding.