u-blox’s New Kits Help Designers Explore Bluetooth Direction Finding

July 01, 2021 by Adrian Gibbons

Two new hardware kits from u-blox use Bluetooth Direction Finding APIs for indoor positioning applications. Are they using angle-of-arrival or angle-of-departure for direction finding?

Indoor positioning and wayfinding technologies are opening up new applications in warehouse automation, asset management in multiple industries, including personnel management. This growth means that Bluetooth Direction Finding, a core feature in the Bluetooth 5.1 specification, is finding its way into more hardware designs.

This week, u-blox revealed a pair of new kits for high-precision indoor positioning, colloquially called ‘Explorer.’ The XPLR-AOA-1 and XPLR-AOA-2 differ primarily in the amount of hardware received in the kit but are both based on the angle-of-arrival (AoA) direction-finding methodology. 


The ‘Explorer 2’ kit, which includes four tags and anchors. Image used courtesy of u-blox


Let's take a look at the hardware available in these kits, the differences in several direction-finding methodologies, and the hardware use cases for different applications. 


Exploring u-blox’s Newest Hardware

The first thing to notice about the XPLR-AOA kits is that they are based on the NINA-B41 series u-connect module. The NINA-B41 series modules are standalone BLE modules that host the entire Bluetooth protocol incorporated into the u-blox C209 tags.

As for the main processor, a Nordic Semiconductor nRF52833 BLE system-on-chip can be found on the u-blox C211 anchor. The Nordic SoC is responsible for collating all of the received RF signals from the various anchors for use in u-connectLocate software.


An example application that uses the XPLR-AOA-2 kit, along with its four C211 anchors and C209 tags.

An example application that uses the XPLR-AOA-2 kit, along with its four C211 anchors and C209 tags. Image used courtesy of u-blox 


The XPLR-AOA-1 kit, on the other hand, is a simplified version of the Explorer 2 kit, offering only a single tag and anchor. u-blox intended this kit to allow designers to test and design angle-of-arrival applications where the angle relative to a single fixed point is sufficient. Its accuracy is equal to the tag range, whereas the XPLR-AOA-2 can create a triangulated signal. 

With this in mind, how has direction finding evolved into a viable product class alongside Bluetooth? What technologies and methods enable the u-blox Explorer kits?


Using Radio to Find Your Way

Finding your way around various triangulation methodologies is a balance of complexity on the tag and the host Bluetooth receiver. There are three main methods for determining indoor positioning.

Relative signal strength indication (RSSI) is the historical method for determining the relative distance of a tagged object. A tagged object would broadcast a beacon signal, which would be read in by a receiver whose sensitivity had been set to a specific threshold for a given object’s range. However, this is not direction finding; it is rudimentary distance finding. 

Today, two other techniques help allow for true direction-finding. Angle-of-arrival (AoA) and angle-of-departure (AoD) utilize RSSI to triangulate a tag location relative to an anchor. 


Two locators (anchors) provide tag location information to a host application.

Two locators (anchors) provide tag location information to a host application. Image used courtesy of Nordic Semiconductor


The following section will cover the basics of both of these triangulation techniques. 


AoA/AoD: Are You Coming or Going? 

Angle-of-arrival (AoA) techniques transmit from the tag device, while angle-of-departure (AoD) methodologies transmit from the host anchor. 

The general form of the two methods, which varies based on application, can be seen below. 


Angle-of-arrival signals tag to anchor.

Angle-of-arrival signals tag to anchor. Image used courtesy of u-blox


In AoA, a signal is propagated from the tag towards multiple receiver antennas, making up the anchor system. An example of an AoA can be seen in the u-blox video demonstration, where it is used to track packages and people [video] as they move through a given space. 

On the other hand, AoD is a more optimized solution for guiding a user to a specific location. The transmitting anchor projects multiple propagated signals, which are received slightly out of phase from each other at the tag. 


Angle-of-departure signals anchor to tag.

Angle-of-departure signals anchor to tag. Image used courtesy of u-blox


For example, an angle-of-departure would make an excellent addition to an application that helps freshman university students navigate specific rooms on campus.

Which method is best for your design?


Making AoA/AoD Design Decisions

Naturally, there are trade-offs for each methodology. AoA techniques place the software processing burden on the anchor, which is likely to be a less computationally constrained device than the tag. 

Conversely, with AoD, the tag must process the phase changes of the various radio signal components and then render application information to the user.

Generally speaking, more processing power will result in additional cost and power considerations. A simple asset tag would benefit most from the AoA method, much like the XPLR-AOA-x kit options.

Alternatively, a cell phone with a significantly more powerful processor could utilize AoD to its fullest potential. 

The new ‘Explorer’ kit from u-blox aims to allow design engineers to evaluate the angle-of-arrival methodology for various indoor positioning applications. 



Have you ever used AoD or AoA methods? If so, how? Let us know in the comments down below.