Bluetooth Scanner with Direction of Arrival Estimation

The problem of determining the direction from which a signal originates has been explored since ancient times — whether to localize a sound source or, in modern contexts, to track the origin of Radio Frequency (RF) transmissions. Building upon this longstanding challenge, this thesis presents the design and implementation of a Bluetooth Low Energy (BLE) scanner capable of estimating the Direction of Arrival (DoA) of BLE signals, with intended applications in search and rescue operations and wildlife tracking. The system employs a circular array of four directional antennas and nRF52840 based BLE receivers to capture spatially distributed signal strength measurements. A Fourier series (FS)-based gain modeling method is used to characterize the directional sensitivity of each antenna, enabling the estimation of DoA using only Received Signal Strength Indicator (RSSI) values, without the use of phase information. The estimation process is formulated as a Separable Least Squares (SLS) problem, allowing efficient resolution of both linear and nonlinear components. To ensure model parsimony and mitigate overfitting, the Bayesian Information Criterion (BIC) is applied to select an appropriate model complexity. Experimental evaluations demonstrate a Root Mean Square Error (RMSE) as low as 7.9°, validating the approach’s feasibility in real-world environments. The resulting system is low-cost, portable, and does not require phase information — highlighting the potential of RSSI-based DoA estimation for robust BLE localization in mission-critical scenarios.