Nordic Distance Toolbox - measurement at high precision

[lubo]

Hello,

I have a problem with distance measurement using BLE. I adapted DM sample from nordic connect SDK to do measurement using "high precision" method. I collected over 100 samples for different distances beween my devices.

As you can see on following diagrams, I get like 2 different measured distances for one real static distance between 2 devices. Do you have any ideas what could cause this effect? The effect takes action not only for "high precision method" but as well as for example phase slope and at different distances.

My setup:

devices: custom boards using NRF52840, pcb antenna

sw: nordic connect SDK v1.9.1, nrf_dm sample

To enable high precision measurement I added following code to dm.c source file:

high_prec = nrf_dm_high_precision_calc();

and enabled CMSIS DSP in project config:

CONFIG_CMSIS_DSP=y

CONFIG_CMSIS_DSP_MATRIX=y

Thank you.

Lubo

[lubo]

Update:

I tested the sample on ublox NINA-b302 modules. I'm not observing the problem. Seems like there is a problem on our custom boards. Any ideas what could be a problem on it?

[Susheel Nuguru]

not really sure. Are you running the same application on your custom board and ublox? 

[lubo]

Yes the same app is running on both of them. Problem occurs in case of ranging with the cb to cb, cb to ublox. Only case ublox to ublox is doing ranging well.

[Susheel Nuguru]

There could be issues with your customer HW, please double check if there are any issues with the antenna path or similar interference noise from close proximity network on the radio path towards the antenna. There are some calibrations that we do to tune away hardware specific offsets and you need to do the same for custom hardware.
In the file nrfxlib\nrf_dm\include\nrf_dm.h -> sruct nrf_dm_config_t -> member dist_offset_err, you can add an offset of the error that your hardware is showing with this solution. This offset will be different for different hardware and with custom hardware, you need to test and adjust these distance offsets that fits for your hardware

[Susheel Nuguru]

what is cb in this context? seems like the cb offsets needs tuning, as ranging involving this device seems to have problem. Hard to say the reason without being able to replicate it on our end.