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I have a strange issue with an FMB120, latest official firmware. GNSS is sleeping (no ignition, no movement), but every three hours reported location changes (Location is in every codec8 packet). I have configured the device to send reports every minute and it's clearly visible. Usually it's insignificant, but sometimes it's up to 100 meters. All AVLs stay the same, only location updates.

 The only recent change I did was turning off the GNSS Static filter (because it was causing another issue) and this could have masked this issue.

On a first glance, the only things that happen periodically at those intervals (or intervals that multiplied could be 3 hours)

  • NTP Time sync - every three hours. I'm using NITZ+NTP instead of GNSS.
  • FOTA - every 30 minutes
The most likely candidate is the time sync, small drifts in RTC might change what the GPS module thinks of the location, especially when GPS is off.
My questions are:
Have anyone encountered this issue?
Is there any documentation for the TM2500 and the embedded platform/SDK/architecture available?

1 Answer

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Hello,

Thank you for your question,

If the static filter option is disabled, the device will not be able to filter the location jumps, while the vehicle is stationary.

Due to buildings or obstacles or any other factors that could block / interrupt / disperse the signal, the location will not be displayed correctly and you will have a various location points sent to server. Please also note that after GNSS sleep the device will take a time to get GNSS fix, if the filtering is not used this will also create a record with different geographical location data.

If you wish to avoid issues like this the static navigation filter should be enabled.

Please inform us on what issues you are having while using "Static Navigation Settings"

Regards.
by

But we have location jumps WITH NO RUNNING GNSS. State is sleeping (as it's supposed to).

I did some tests, and disabling periodical NTP sync and using GNSS as the only time source fixed this issue.

About the static filtering - here is why we have decided to turn it off

Here is our setup:

  • - Movement source is ignition & accelerometer
  • - Movement stop is 10 seconds
  • - Device is configured to do GPS Sleep in some time

And what happens:

  • Device is in GPS Sleep state
  • Vehicle (Scooter) gets some vibration, movement is detected, GPS turns on.
  • After 10 seconds, there is no good gps location - we might have fix, but it's inaccurate. Movement ends (10 second timeout) Static navigation filtering kicks in, location field is frozen.
  • 10-20 seconds later, gps fix is obtained with good accuracy (based on number of sattelites, hpop/pdob). In the report we keep receiving the bad location (latitude and longitude same as previous report), but parameters report good fix (current number of sats, hdop/pdop low).

This misleads our system that we have a good GPS location, but in fact we're getting location obtained 10 seconds after GPS was awaken (and is inaccurate).