Introduction#

Bluetooth 5.1 introduced support for Direction Finding by adding the option to send and receive Constant Tone Extensions (CTEs) after Bluetooth packets. This makes it possible to do phase measurements on antenna arrays and ultimately to determine the direction of an incoming signal. To learn more about the theory of Direction Finding, that is how to determine the direction of incoming signals, see Bluetooth® Direction Finding Fundamentals. Readers of this document should be familiar with the basics and terms of Direction Finding.

Beginning with Bluetooth SDK v3.1, Silicon Labs’ Bluetooth stack supports CTE transmitting and receiving features on selected devices and can take phase measurements on the incoming signal as specified by the Bluetooth standard. Note, however, that the determination of the angle of incidence from the phase measurements is outside of the scope of the standard and must be implemented in the application. To reduce the Time to Market for its customers, Silicon Labs also offers a reference implementation of a Bluetooth-based Real Time Locating System (RTLS), which provides both an out-of-box experience to evaluate the solution and a flexible framework that makes it possible for everyone to create their own RTLS. To get started with the reference implementation, refer to Application Development with Silicon Labs’ RTL Library. To find the API Reference Manual for the RTL library, visit https://docs.silabs.com/. The link for the RTL library is under the Bluetooth section. To learn about the Simplicity Studio tools supporting Direction Finding, see Using the Bluetooth® Direction Finding Tool Suite.

It is of course also possible for anyone to use their own direction-finding algorithm on top of the Bluetooth stack. This requires deep knowledge in Direction Finding but enables even more flexibility. If you choose this approach, see Custom Direction-Finding Solutions using Silicon Labs’ Bluetooth Stack.

The Silicon Labs Direction Finding solution is part of the Bluetooth SDK. If you are not yet familiar with the Silicon Labs Bluetooth SDK, start with the Bluetooth SDK Getting Started Guide.

Finally, either you use Silicon Labs’ Direction Finding board or your own design. AN1195: Antenna Array Design Guidelines for Direction Finding provides you with useful information regarding antenna design. It also provides accuracy measurement results of the RTL library used with Silicon Labs’ Direction Finding board.