Introduction#

This document explains how The Silicon Labs Bluetooth stack supports Direction Finding. Before going forward, the reader must have a basic knowledge of Direction Finding. To learn the basics, refer to Bluetooth® Direction Finding Fundamentals. Reading the Technical Overview of Bluetooth direction Finding published by the Bluetooth SIG is also recommended.

Direction Finding, which is estimating the angle of the incoming signal, is based on the concept of antenna arrays, where multiple antennas specially arranged in space sample the same reference signal. The reference signal is a continuous wave where both frequency and phase are maintained over a time interval long enough to be sampled on all antennas. The samples are then turned into phase differences, and phase differences are turned into angle estimation.

Since Bluetooth 5.1 introduced Constant Tone Extensions (CTEs) that can be applied after regular Bluetooth packets, the Silicon Labs Bluetooth stack makes it possible to sample these extensions on different antennas and provide the antenna samples to the application. This document explains the antenna sample format. The samples can be used by anyone who wants to implement their own direction-finding application that turns antenna samples into angle estimation.

If you are unfamiliar with direction finding, or if you are familiar with the concept but you do not have a deep understanding of angle estimator algorithms, Silicon Labs strongly recommends using the RTL library in your application. The RTL library provides a full solution to calculate the angle of the incoming signal from antenna samples in a real world environment. To learn more about the Silicon Labs solution, refer to Application Development with the Silicon Labs RTL Library. If you decide to continue development using the Silicon Labs RTL library, you can skip this document.