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.

[greentree]

Hi Robwasab,

Thank you. As I see now,  I missed “The IQ samples are recorded with respect to the RX carrier frequency” sentence in the spec and decided the sampling is made over demodulated signal without referring to the carrier. Strange, the developers did not point me that out.  It is great if I was wrong. Hopefully PLL jitter will not make significant phase noise.

“I agree that this is not the cutting edge MUSIC algorithm”

MUSIC is a fundamental algorithm. It requires making distance between antennas not more the half of wavelength for unambiguous AOA detection.  Max distance between antennas in array defines the accuracy of AOA estimate. We need many antennas if we need accurate AOA estimation with MUSIC.  The more antennas, the more eigenvalues have to be calculated in the algorithm. Correspondingly, more resources and time for calculation are needed.  It affects the system throughput quite well. Other methods would be more effective in low cost applications. For instance, methods based on disambiguation from one baseline to another one.

[bloobird0]

Hello,

what is the current status?`Is there any dev kit with antenna array that we could use to get into direction finding without having to make custom hardware for it?

[Simonr]

Hi Fabrice

No, we at Nordic do not have a finished product with an antenna array at this moment. If you'd like more details on if and when this will be available, please contact your regional sales manager. If you don't know who this is, please fill out the sales related questions form here and they should get back to you with a detailed answer.

Best regards,

Simon