Nordic Distance Measurement sampling rate

[franck]

Hello

We are interested by measuring distance on very short range (less than 3m) so MCPD phase slope will fit well for us

Currently time to get distance is too long (we've evaluated using sample in nrf connect sdk) and we would need to know if there are way to improve it

Would it be much faster if dm api(dm_request_add) would only compute phase slope estimation (and not ifft ....) ??

Also we know the BT address of the peer, is there any faster way to synchronise than advertising,scan/scan response ?

Thanks

[Elfving]

Hello Frank,

We are interested by measuring distance on very short range (less than 3m) so MCPD phase slope will fit well for us

Sounds like a plan!

Would it be much faster if dm api(dm_request_add) would only compute phase slope estimation (and not ifft ....) ??

The CPU time used to do phase-slope estimation is probably faster than IFFT if that is what you mean. However right now we do not have a way of running one without the other (IFFT and phase slope are part of the same API. These wont be split up for the time being). 

Though it is possible for you to run your own proprietary estimation on the measurement data if you want to! You could just implement a simple phase-slope algorithm that uses the IQ that is in the nrf_dm_report_t.

Also we know the BT address of the peer, is there any faster way to synchronise than advertising,scan/scan response ?

This depends a lot on the setup, I think. In the sample, we use adv/scan for synchronization to demonstrate the operation of the DM at the same time as running the GATT service. Though other ways are possible.

• If it is between individual devices, then I think using radio notifications you might be able to have a better synchronization. 
• If you can have fixed roles (a fixed initiator and a fixed reflector), you could only run a scanner or advertiser. Then you could tune the scanner to use continuous scanning, I think.

In general, you can tune the adv/scan parameters to speed up the initial synchronization. After that, you could reduce the time between measurements to the same device, if that is desired.

Regards,

Elfving

[xu shengxian]

Hello  Elfving,you said

Elfving said:

Though it is possible for you to run your own proprietary estimation on the measurement data if you want to! You could just implement a simple phase-slope algorithm that uses the IQ that is in the nrf_dm_report_t.

Can IQ data really be extracted from official examples? I have made relevant attempts, but it seems that the code is precompiled and I don't know how to extract IQ data to calculate distance using MCPD algorithm.

“Bluetooth: nRF Distance Measurement with Bluetooth LE discovery”

“nrfxlib API: nrf_dm/include/nrf_dm.h Source File”

Looking forward to your help!

[Elfving]

Hi,

It is true that the code is precompiled, though the IQ data should still be retrievable.

I do believe the MCPD is one of the algorithms that the nRF_dm sample uses by default, though you should be able to implement and use it yourself if you prefer to do it that way.

Regards,

Elfving

[xu shengxian]

Thank you！