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1 year, 11 months ago.

Can not get GPS Fix

Hi all,

I have a problem to get a GPS fix with my Dragonfly. I'm using mbed OS5 wit the MTSCellularInterface-master library. Data connection works fine.

This is the part of the code where I'm checking the fix and reading the GPS data. This code is in a loop.:

if (radio->is_gps_enabled()){ logInfo("GPS is Enabled"); } else { logInfo("GPS is NOT enabled"); radio->gps_enable(); } if(radio->gps_has_fix()){ lastPos = radio->gps_get_position(); logInfo("Fix OK");

} else { logInfo("Obtaining GPS fix"); }

The debug output is:

[INFO] AT$GPSACP? = AT$GPSACP?

$GPSACP: ,1,

OK

[WARNING] No GPS fix. GPS fix can take a few minutes. Check GPS antenna attachment and placement.

Any help is appreciated as I'm stuck!

Kind regards,

Adriaan

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The MultiConnect® Dragonfly offers developers an FCC and carrier certified solution that makes connecting sensors and other edge-of-network devices quick and easy.
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1 Answer

1 year, 11 months ago.

Hi Adriaan,

Have you tried with your GPS antenna outdoors or at a window with an unobstructed view of the sky? Obtaining a good signal indoors may not work.

Kind regards, Leon

Hi Leon,

Yesterday I finally got a GPS FIX. So that took away my doubts about my coding at least. And yes I did put the antenna outside. But then it still takes HOURS or even longer to get a fix. Is there a method of obtain the fix faster. Looking at some Telit articles there is something like Assisted GPS. https://www.telit.com/products/positioning-and-timing/bundling-with-cellular-assisted-gps/ Do you know if anyone looked into this? Would be great if the MTSCellularInterface would support this. Now I must say that I only tested out of my lab (with antenna outside) and I need to see in a couple of weeks how the field testing will go. Kind regards, Adriaan

posted by Adriaan Kooderings Clemens 17 Oct 2017

Hi Adriaan,

If you are seeing hours to acquire a fix, I think there is more to your problems than TTFF (time to first fix). From Telit documentation... "S-GPS is sometimes slower to compute its First Fix; this phenomenon is evident in very poor signal conditions, for example in a city where the satellites signals are corrupted by the multipath propagation." "A "cold" start indicates the scenario in which the GPS must get all data in order to start navigation, and may take up to several minutes." In my experience, I have seen very long times or no signal when my antenna is inside but at a window it acquires a fix in a couple minutes. The window I test at does not face tall buildings or other obstructions.

I am familiar with A-GPS but have not worked with it. I will submit a feature request for MTSCellularInterface. It could be added as part of the library or as an example program. The MTSCellularInterface allows sending AT commands of the users choosing to the radio.

Kind regards, Leon

posted by Leon Lindenfelser 17 Oct 2017

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