Using nRF52811 for direction finding

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.

  • Hi

    Sorry for the late reply, but I have not been able to find the answer to questions 1 and 2, so I am waiting for an answer from our experts on the matter. 

    In the meantime, I can give you an answer to question 3. You will not need to use two separate nRF52811 systems, as one should be sufficient for very accurate position finding. The nRF52811 antenna will be an antenna array, which allows it to find the AoA and AoD accurately without two separate receivers. So you will not need a specific approach to use the position finding feature. Please read more on how Nordic will implement Bluetooth 5.1 here.

    Hopefully I'll be able to come back to you on questions 1 and 2 soon.

    Best regards,

    Simon

  • Hi Simon,

    Thank you for the fast answer. However...

    Information over the link you provided doesn't include explanation regarding how one receiver can be used for coherent signal processing in direction finding. We can try to estimate direction of arrival based on magnitude of IQ samples for every antenna in array, but it will be highly vulnerable from multipath propagation especially in indoor environment. So, such approach will be highly inaccurate and comparable with accuracy of RSSI based methods. Whereas indoor location based services are starving for high accuracy.

    Does Nordic have plans for making a Bluetooth 5.1 chip with two coherent receivers, if answers for questions 1 and 2 are negative currently?

    There is no need of full duplication of whole current chip functions. Only second receiver working with the same LO and synchronized IQ sampling in both receivers are needed.

    Best regards,

    Vlad.

  • Here on DevZone we never speculate or talk about what might happen in the future, so this question is better suited for your Regional Sales Manager (RSM). If you need his contact information, let me know and I will help you get in touch.

    Best regards,

    Simon

    PS: I will of course update you when I have answers on your initial inquiry.

  • Thank you Simon. 

    I asked that question because developers, not sales, make the future. However, you are right, that is not the place for such discussion. I appreciate your answers.

    Best regards,

    Vlad.

  • Hi Vlad

    I got some input from one of our 52811 experts, and here is what he said regarding the initial inquiry: 

    BLE AoA is based on IQ sampling from different antennae sequentially with a single receiver chain. For this a single nRF52811 is connected to an external antenna switch and then to multiple antennas. A system as described in questions 1 and 2 is not something we have investigated. We recommend to use the AoA method described in the Radio - Direction Finding (6.14.12) chapter of the nRF52811 product specifications.

    I hope this is a satisfactory answer, and if you have any follow-ups, please ask!

    Best regards,

    Simon

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