Fundamentals and theory on direction finding using Bluetooth, a user guide from Silicon Labs. Link here (PDF)
Bluetooth Angle of Arrival (AoA) and Angle of Departure (AoD) are new technologies that establish a standardized framework for indoor positioning. With these technologies, the fundamental problem of positioning comes down to solving the arrival and departure angles of radio frequency signals. This document explains the basics of these technologies and provides the theory behind estimating angle of arrival.