NRF9160: GPS Tracking satellites, but can't get fix.

Hi, we have a custom board using the nrf9160, running modem firmware 1.1, and using the nrf9160_gps driver.

Sometimes we see messages like this:

Tracking: 8 Using: 0 Unhealthy: 0

Where the GPS is tracking satellites but is not using any, and never gets a fix. Eventually we time-out and stop the GPS. But this behavior continues until the next device is restarted.

Is this a bug with the modem firmware? Is there any fix for this.

Thanks

  • I'm working on getting a modem trace.. Do you need to see the Log output as well?

  • Yes, please. 

    Where are you conducting your tests? Where is the GPS receiver when you are tracking the satellites?

  • Is there any news on this issue? I do see the same issue with tracking several SVs but not using any of them on my Thingy 91 occasionally happening too.

  • Just dropping in on this question... I was under the impression that the LTE and GPS couldn't be operated at the same time, you can't use them simultaneously they have to be switched in between. So how can the LTE generate intermodulation to the LNA then?

    Peter 

  • We are still trying to reproduce this issue on a device running the modem trace however, we have found some pattern on one of the devices that has been running for a longer period. The pattern is as follows:

    1. The device runs as expected with great (30~60s) TTFF
    2. After approximately 6~7 days we enter this failure mode where the device is tracking many SVs but using 0 and times out (20 minutes)
    3. On the next GPS fix attempt (6 hours later), once again it tracks many SVs and uses 0.
    4. At this point we do a software reset
    5. On the next GPS fix attempt (6 hours after software reset), the fix is successful (again with a very good TTFF)
    6. After this the next few GPS attempts all time out
    7. Steps 4-6 repeat maybe 3-4 times before we finally come out of this mode and things work again for another 6~7 days

    Based on this it almost seems like an almanac update might be somehow responsible.

    • Can Nordic confirm how often an almanac download is attempted?
    • What happens if an almanac download isn't able to complete in the 20 minutes? Is it thrown out until the next fix attempt or is partial download possible?
    • What happens on reset? Does the firmware maybe revert to the last known almanac and that's why our first fix is successful before it attempts to download the new almanac?
    • Is there anyway to get information about the status of the almanac download status in the device firmware?
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