Using nRF52811 for direction finding

[greentree]

nRF52811 has only one receiver. Most accurate direction finding can be made based on estimation of phase difference between two signals received in two spaced antennas. Such phase difference can be accurately estimated if we take samples in two receiving channels at the same moment. So, two receiving channels shall have the same coherent LO source and samples shall be made synchronously. Correspondingly, I would like to ask have 3 questions:

1. Can we use two nRF52811 systems with the same coherent LO source?

2. Can we synchronize IQ sampling moments in both nRF52811 systems?

3. If question 1 and 2 are negative, what AOA estimation approach shall be used with nRF52811 ?

If my questions are incorrect, I would appreciate any clarifications regarding that.

[Simonr]

Hi Vlad

We currently don't have these details/measurements in place as this is work in progress.

Best regards,

Simon

[greentree]

Thank you Simon,

Maybe somebody from DevZone tested that method using SDR? 

Unfortunately, theoretical estimation of the method doesn't look encouraging. Assume we have 1 meter distance between antennas  and measure phase difference between signals of 500kHz. If AOA will be changed from 0 to 30 degrees, corresponding phase difference will be changed from 0 to 0.3 degree... Real phase errors may be over 1 degree. Utilization of multiple baselines will slightly improve accuracy of measurements, but we need to increase frequency of the signal and distance between antennas significantly to achieve acceptable accuracy of the system. If we increase frequency, it goes out of Bluetooth conception. Even 1 meter of distance is a quite large size of antenna array for indoor applications.

I appreciate any comments. Maybe I missed something?

 

[greentree]

Hi Simon,

I would like to clarify one more question to understand how it may work in a good way.

Does nRF52811 have a two channels receiver? Only "yes" or "not" would be enough.

Best regards,

Vlad.

[Simonr]

No, it does not.

Best regards,
Simon

[greentree]

Hi Simon,

I would like to ask you a question via email. Is that possible?

Best regards,

Vlad.

[Simonr]

Hi Vlad

Due to the Easter holiday you will have to expect a delay in answers, sorry for the inconvenience!

No, you can't. If you have private questions I suggest you create a Private ticket on the forum. This way the ticket will only be visible to you and Nordic engineers, and it will be treated with confidentiality.

Best regards and Happy Easter,

Simon