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  • Case ID: 289275
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Direction finding AOA with nRF52833

user116169

Hi,

I have program two nRF52833, one as transmitter and one as receiver (with zephyr project called "direction_finding_connectionless_tx" and "direction_finding_connectionless_tx"). I have an antenna array with 4 antenna patch.

But i have a problem, i have not the angle of arrival and i have not always the same result:

Sometimes i have the CTE that appears and sometimes not.

I have the impression that the main stop at the line 359:

My receiver see my transmitter as you can see but what i have to do to see the angle of arrival ?

Please i'm lost and if someone can help me i'm more than interested.

  • +1

    I have resolv my problem: my tx was not configure in AOA mode so i just add "CONFIG_BT_CTLR_DF_ANT_SWITCH_TX=n" in "prj.conf" (edit with notepad++

  • 0

    Hi

    I'm afraid the screenshots you have uploaded are too low of a resolution for me to read properly. Could you upload them as logs instead perhaps? 

    Please note that the output you see from these samples won't be the "finished" angle of arrival, as this just transmits the raw IQ data to your central device. It is up to you to add an AoA algorithm that handles these values and converts them into readable data. Nordic will not provide the direction finding algorithm, and customers/users are expected to get that elsewhere. In order to use the IQ data you get from the beacon you will need an AOA algorithm, which we don't provide. There is no point in looking at the raw data as it needs to be converted into vector form to review it properly. You can check out this page for information on the various formulas used to translate IQ data between polar and rectangular form. 

    It's also worth noting that an antenna array with only 4 antennas in total will not provide great accuracy, and we recommend 12 or more antennas in an array for good accuracy.

    Best regards,

    Simon

  • 0 in reply to user75734

    Thank you for the reply.

    Yeah i now that i will have to use an algorithm to convert IQ data in AOA.

    I can now receive IQ data from 45 samples.

    But i have a lot of questions:

    - did i have to receive 45 samples for each antenna or i have to receive 45 samples in total (i suppose it's for each antenna but i'm not sure).

    - How can I switch my antenna because i have to command them by send them 3.3V or 0V (for 1 or 0 to select the antenna that correspond to the command(00/01/10/00))

    - Is there an antenna that works well with the program "direction_finding_connectionless_rx"

  • 0

    Hi

    1. You can set the number of samples you want to receive to fit your application, where have you gotten the number 45 from?. The total number of IQ samples provided by the IQ samples report varies. It depends on the CTE length and the antenna switch slot length. There will always be 8 samples from the reference period, 1 to 37 samples with 2 µs antenna switching slots, 2 to 74 samples with 1 µs antenna switching slots, meaning 9 to 82 samples in total.

    2. The antenna switching is done by 2 GPIOs that switch in the pattern that ant_patterns is set in in main.c. The GPIO switches the antennas based on the slot length you have set. More information here.

    3. You can contact the regional sales manager of your area for more information on fitting antenna arrays provided by us or third parties, as they would have a overview of what is available in your area. If you don't know who to contact, fill out the sales related questions form here to get in touch.

    Best regards,

    Simon

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