AN1297: Custom Direction-Finding Solutions using the Silicon Labs Bluetooth Stack

PublishTime：2021-05-08

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 measure the phase of the incoming signal on different antennas.However,calculating the direction of the incoming signal from the measured phases is the responsibility of the application,and not of the Bluetooth stack.This document explains the interface between the stack and the application regarding phase measurements to enable implementing custom direction-finding solutions using Silicon Labs’Bluetooth stack.The information in this document provides an alternative to using the Silicon Labs customizable reference implementation,and is intended for developers who have a deep understanding of direction-finding algorithms and prefer to develop their own solution.
Developers who prefer to start with the Silicon Labs customizable direction finding solution should refer to AN1296: Application Development with the Silicon Labs RTL Library instead of this document.
●KEY POINTS:
■Constant Tone Extension
■Antenna Switching
■IQ samples
■Phase compensation
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.
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 AN1296: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.

Brand of Product：	Silicon Labs
Part#：
Product Category：	Bluetooth Stack More
Application：	More
Data Type：	Application note & Design Guide More
Safety & Environment Standards：	More
Operating Temperature：	Please see the document for details
Qualification Grade：	More
Qualification Approval：	More
Package：
Language：	English Chinese Chinese and English Japanese
Date of Creation：	2021/01/01
Version Number：	Rev. 0.
Data Encoding：	AN1297
Data Size：	2.2 MB

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