Channel sounding tips & tricks? Do i need a second antenna?

[silaOzer]

Hi,

I am working on a project with channel sounding requirements and I have collected some test data. I am using the example codes Bluetooth: Channel Sounding Initiator with Ranging Requestor and Requestor one. However data is not accurate or precise. I have also tried outside and accuracy still isn't perfect. The data also fluctuates a lot. I heard adding a second antenna might help.

We are using nrf54l15-dk. 

So my questions are:

1. What are the data analysis tips & tricks people are using? Is median better than calculating mean? Or what are the cs parameters i can change to get more accurate results? Ifft is tway better than the other data. Why is that?

2. How can i add a second antenna? Datasheet and documentation for the board wasnt super explaining.

[PaKa]

We normally use a median filter as the noise is not normal distribution noise. 3 stage is usually quite good. Having more than one antenna on at least one side makes the ranging more robust as you can then detect multipath issues. You can see this as each measurement isn't more accurate but you can get rid of some of the bad ones. This can give a more reliable ranging. And we recommend the IFFT algorithm as it is usually the better. 

[silaOzer]

Great, how can i add a second antenna to the dev kit? And what is 3 stage?

[PaKa]

You need to find a fast RF switch and design HW with the switch. Easiest path is probably a custom kit or test with a kit from one of the module partners with 2 antenna boards. Euzerio should have one.

When you make a Median filter you add stages and then you pick the middle value. These will normally be odd number of stages as you then have a clear center value. 3 stages is the shortest you can do, longer is usually better but will have longer latency for changing values. We have seen that the improvement for more stages when it comes to Channel Sounding is not that large so 3 is OK.

[silaOzer]

Amazing thank you!

So do I have to modify the code? This is not related to the mode 2-3 am I right? That is for if we are doing rtt or pbs?

Ill look into the dev kit. We currently might not have the budget to change the kit, so I was wondering is there any add on boards for nordic devkit to add extra antennas?

Again thank you for the fast reply!!!

[PaKa]

Yes, adding more antennas or RF path support in the initiator will require you to change the code in the sample.

The Bluetooth stack supports multiple RF paths and multiple antennas but the default configuration may not enable this. For the initiator you will also need to add code that takes the data from each of the RF paths and calculate the IFFT for each of them. Some work but should not be too difficult.

For the HW; no, there is no plug ins available for multi antenna usage. If you are limited then I would suggest to test with the single antenna and rather add a dual antenna solution when you spin your first HW.