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  • Case ID: 361197
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Synchronization over LTE/NB-IoT - SNTP time accuracy

mjaszczykowski

Hi,

We are developing an application that requires synchronization between two or more nRF9160-based devices. We have the following requirements and constraints:

  • Required time synchronization accuracy: < 1 ms
  • GNSS is not available — devices are deployed underground without access to an external antenna
  • Both devices connect via LTE-M / NB-IoT

We have the following questions:

  1. What is the expected accuracy of SNTP time synchronization over LTE on the nRF9160?
  2. What is the expected accuracy of LTE network time received via NITZ or SIB16 (configurable via AT%XNETTIME)?
  3. Are either of these solutions capable of meeting our < 1 ms accuracy requirement?
  4. Are there any other Nordic-supported time synchronization solutions that could meet our accuracy requirement given our constraints?

Any guidance or alternative approaches would be greatly appreciated.

Thank you.

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  • 0

    Hi,

    What is the expected accuracy of SNTP time synchronization over LTE on the nRF9160?

    While NTP can achieve sub-ms resolution on cabled networks, I would not expect too much from SNTP over an LTE network. Maybe around 100 ms could be achievable, but highly dependent on the network operator.

    • What is the expected accuracy of LTE network time received via NITZ or SIB16 (configurable via AT%XNETTIME)?
    • Are either of these solutions capable of meeting our < 1 ms accuracy requirement?
    • Are there any other Nordic-supported time synchronization solutions that could meet our accuracy requirement given our constraints?

    I will need to look further into this, and expect to have more answers within a couple of days.

    In the meantime, I highly encourage the community here on DevZone to weigh in.

    Regards,
    Terje

  • 0 in reply to tesc

    Hi,

    tesc said:

    • What is the expected accuracy of LTE network time received via NITZ or SIB16 (configurable via AT%XNETTIME)?
    • Are either of these solutions capable of meeting our < 1 ms accuracy requirement?
    • Are there any other Nordic-supported time synchronization solutions that could meet our accuracy requirement given our constraints?

    I will need to look further into this, and expect to have more answers within a couple of days.

    Unfortunately, the intended way of acheiving such precision with the nRF9160 is to use the 1PPS GPS signal.

    I think it should be possible to get close to 1ms precision for time synchronization between devices if you handle the SFN counter by yourself. But this is not a " properly supported" way of doing it.

    Best regards,

    Simon 

  • 0 in reply to Simon D-M

    Thank you.

    Could you give me any hint on how to access SFN counter?

  • 0 in reply to mjaszczykowski

    Hi,

    The SFN counter is available in the PRS reception (link).

    Best regards,

    Simon

  • 0 in reply to Simon D-M

    Thank you. Just two additional question if I may.

    1. Is there any additional piece of the documentation?
    2. Is this available only for nRF9151? Am I reading it correctly?

Reply Children
  • 0 in reply to mjaszczykowski

    Hi,

    No worries, feel free to ask as many question as you want :)

    mjaszczykowski said:
    1. Is there any additional piece of the documentation?

    On the SFN counter, not really... Using it for time synchronization is not really something we planned. It just happens to be possible. So we don't have any documentation or libraries on that behavior...

    mjaszczykowski said:
    2. Is this available only for nRF9151? Am I reading it correctly?

    I've actually never tried to use it, but it looks like it should be possible to access it on both nRF91... Where did you read that? Are you having issue to get the SFN ?

    Best regards,

    Simon

  • 0 in reply to Simon D-M

    Regarding 2.

    If you go to the main page of the RS capture API. There is a note about the modem firmware:

  • 0 in reply to mjaszczykowski

    Hi,

    Sorry, I wasn't aware of this...

    Then unfortunately yes, it looks like it is only possible to use them on the nRF91x1.

    And to come back to the initial question, with the SFN counter out of question, I can't really think of anything else that could achieve that kind of resolution on the nRF9160 without using GNSS...

    How far are you into the development? Would you be able to migrate your devices to the nRF9151?

    Best regards,

    Simon

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