RE: How to Implement BLE-Based Localization with nRF52832 Without CTE?

Elfving — Fri, 07 Mar 2025 17:20:38 GMT

Hi,

[quote user=""]BLE Transmissions Use Chirps, Not Continuous Waves:[/quote]

BLE uses GFSK, but I am not sure it would be correct to say chirps. Don't mistake it for CSS.

[quote user=""]CTE (Constant Tone Extension) Is Not Available on nRF52832[/quote]

Correct.

[quote user=""]Alternative BLE Localization Techniques Exist:[/quote]

Direction finding, the tools in NDT, and Channel Sounding are your three options here.

I would recommend you to have a look at this webinar we had on the Nordic Distance Toolbox, which explains a bit about the underlying technology, the accuracy, etc. Note the performance section and standard deviation of the different methods mentioned there.

Direction finding and Channel Sounding operate using CTEs, and NDT is our propriatery solution for this. The accuracy you get with DF and CS depends to a large degree on the algorithm you implement to calculate the angles based on the CTE (this is not something we provide), so it is hard to say something about the accuracy there. The NDT calculate the distance using multiple methods at the same time, so that you can for instance take advantage of RSSI when close, and RTT when further away. I think you also can use the IQ data directly (what you get from the CTE) for your own algorithm if you prefer that.

[quote user=""]The system will operate in a complex medium such as the human body, where signal propagation is highly variable.[/quote]

Inside a human body? There are a few things like human bodies and water that don't work too well with 2.4GHz signal propagation. People walking around in the warehouse can be enough to make things difficult for you, inside a human body sounds worse.

[quote user=""]What is the best localization method for the nRF52832 using BLE? Ideally in the cm range of accuracy, as the operational space to localize this BLE emitting pcb is within a 0.5x0.5x1m area. Most literature online describes localization performed in large rooms, giving higher acceptable margins of error.[/quote]

The best method to measure the distance might be a complex combination of direction finding and channel sounding, but it still might be hard to get the accuracy you need. And if you are forced to use the nRF52832 you are a bit limited. NDT is supported on nRF52832 though, have a look at our sample for it.

So RSSI is surprisingly often used, but is not something I recommend, and is definitely not something that will give you the results you need.

[quote user=""]Is there a way to generate a "continuous tone" or workaround the lack of CTE on nRF52832?[/quote]

The NDT takes advantage of some ways. You could make propriatery solutions for this, but that is not something we "support", as in "help you doing".

[quote user=""]Has anyone successfully implemented high-accuracy BLE localization on nRF52832?[/quote]

I don't have an public overview over this unfortunately. There are a few mentioned here, but not everyone wants to be public.

I think using the NDT is your best bet, though with the accuracy requirements you mentioned you might also want to look into UWB.

Regards,

Elfving