Direction Finding

overview

Silicon Labs’ Bluetooth solutions for Direction Finding applications brings a new dimension to indoor asset tracking and positioning. The Bluetooth 5.1 specification enhances location services with a direction finding feature that makes it possible to detect the direction of a Bluetooth signal.  

Applications for Direction Finding

• Point-of-Interest
• Item Finding 
• Real-Time Locating (RTLS)
• Indoor Positioning 

The two direction finding systems are Angle of Arrival (AoA) and Angle of Departure (AoD). With these technologies, the fundamental problem of locationing comes down to solving the arrival and departure angles of radio frequency signals. In AoD, the receiving device is able to calculate its own position in space using angles from multiple beacons and their positions (by triangulation). In AoA, the receiving device tracks arrival angles for individual objects. Still, it is good to note that different combinations of these can be performed; so, these techniques do not limit what can be done at the application level. Both in Bluetooth AoA and AoD, the related control data is sent over a traditional data channel. Typically, these techniques can achieve a couple of degrees angular accuracy and around 0.5 m locationing accuracy, but these figures are highly dependent on the implementation of the locationing system.

design considerations

Angle of Arrival 

• Assets only need a single antenna, can be low power, and simultaneously support additional Bluetooth LE functionality 
• Locators require 3 x 3 or 4 x 4 antenna arrays and switches
• Edge gateways process angle readings and communicate to an asset management system in the cloud to determine device location Angle of Departure
  

Angle of Departure

• Beacons require 3 x 3 or 4 x 4 antenna arrays and switches 
• Mobile devices like smartphones need to support AoD algorithms 
• Beacon coordinates must be known by the location services system

Bluetooth Angle of Arrival and Angle of Departure are new emerging technologies that can be used to track assets as and for indoor positioning and wayfinding. These are phase-based direction finding systems that require an antenna array, RF switches (or a multi-channel ADC), and processing power to run the estimation algorithms. Designing a proper antenna array, as well as an angle estimation algorithm are essential for a RTLS system. Strong performing estimator algorithms are often not computationally cheap. Other positioning technologies include (but are not limited to) RSSI based methods and ToA based methods, but only phase-based AoA/AoD currently have a standardized framework in Bluetooth.

block diagram

AoA is a phase-based direction finding system used for asset tracking, indoor positioning and wayfinding. 

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