distance tool box - IQ data and hopping sequence

[eleven-x_devteam]

Hi,

I am trying to get IQ data from nrf_dm_iq_tones_t and hopping sequence from nrf_dm_get_hopping_sequence with some clues from  RE: Using proprietary ranging stack instead of nordic distance toolbox 

I can see data but when I sort the data with frequency index, it doesn't seem to be linear for both local and remote.

Here are some questions.

1. The IQ data array size is 80 and the hopping sequence array size is 75 then how can I match them?

I saw the first 4 values and the last value of IQ data are always 0 so I assume that the 75 hopping sequence fits 5th ~79th data of IQ data, is that correct?

2. "55 57 44 17 40 51 22 68 16 9 56 27 18 64 25 75 53 14 67 19 63 23 65 77 7 13 46 50 48 43 38 11 62 28 31 10 24 70 4 34 59 66 73 39 41 15 20 76 6 21 49 8 72 35 71 12 36 30 45 78 32 60 26 29 74 42 54 37 61 52 58 5 33 69 47"

 This is one example of the hopping sequence index and it seems that each device keeps using always same sequence even after reboot. Is that correct or do I need to do something more to get right values?

Thank you.

[RachelK]

Hello Elfving,

Thank you for your response. I have been able to extract the hopping sequence with nrf_dm_get_hopping_sequence() when building the application on the network core. 

I have one more question, that might seem obvious but unclear to me, but why is the size of the IQ data 80 instead of 40, given that BLE only uses 40 frequency channels?

Kind regards,

Rachel

[Elfving]

Hi Rachel,

RachelK said:

I have been able to extract the hopping sequence with nrf_dm_get_hopping_sequence() when building the application on the network core. 

Glad to hear it!

RachelK said:

I have one more question, that might seem obvious but unclear to me, but why is the size of the IQ data 80 instead of 40, given that BLE only uses 40 frequency channels?

I think this is for the same reason mentioned in this previous case.

Regards,

Elfving

[RachelK]

Hello Elfving,

I did an inverse Fast Fourier Transformation both over all channels ranging from 2404 to 2478 MHz as well as over all even channels in this range (which should be the BLE channels). Strangely enough I get a significant better results if I perform an IFFT over all 80 channels. Do you have any idea why?

Regards,

Rachel

[Elfving]

That would make sense to me. I just checked with our NDT team, and yes - the NDT does use more than 40, 80 might be correct. NDT is a proprietary solution after all, and the HW does allow access to more than what BT SIG specifies, so there is no reason to avoid using more channels.

Regards,

Elfving

[RachelK]

Thank you for your response! This makes it much more clear.