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

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

gscultho — Fri, 10 Jul 2020 19:18:21 GMT

I was facing the same issues reported in this thread and have reported my solution at the following link:https://devzone.nordicsemi.com/f/nordic-q-a/63591/nrf9160dk-gps-not-getting-fix

For anyone facing the issue of tracking many SVs but not getting a fix, I suggest reverting to an old modem firmware version. In my case (hardware version 0.9.0) modem firmware version v1.1.1 resolved the issue.

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

LordLucan — Wed, 01 Jul 2020 09:02:41 GMT

I too have hit this trough of tracking a number of satellites but never getting a fix. The GPS was working reasonably well. All of a sudden since yesterday it just cannot get a fix. My nrf9160_pca10090 is sitting in an open space outside on the grass. It is tracking about 12 satellites, using 0, it has been like this for about an hour. I'm just using the GPS sample. I'm using the external active GPS antenna supplied. Firmware version 1.2.

There are a number of threads on this forum with similar issues of the GPS just not being able to fix despite tracking a number of satellites. Is Nordic invetigating this issue or suggesting a workaround to reset the modem?

Regards,

Paul

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

jwhite — Wed, 17 Jun 2020 15:09:46 GMT

RicardoPereira I was having this issue indoors, using a large passive GPS antenna. I moved my nrf9160dk closer to my window and it was able to get a fix only using 5 satellites within 45 seconds. I never got an answer as to why a fix could not be found using 9 satellites, and I could not find a forum post that digs farther into this issue.

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

Jan Tore Guggedal — Wed, 17 Jun 2020 06:29:50 GMT

Hei Ricardo (and others having the same issues of seeing many satellites tracked, but no fix),

There's a PR that can help us debug this issue a bit without capturing modem traces: https://github.com/nrfconnect/sdk-nrf/pull/2385

This PR introduces NMEA-only output to the GPS sample (found in samples/nrf9160/gps/), which might help us narrow down what's going on.
Until the PR is merged into NCS, you can experiment with it by using git and pull in the changes like this (assuming your NCS git remote is named "ncs", otherwise change it to your remote's name):

git fetch ncs refs/pull/2385/head
git checkout FETCH_HEAD (add " - b <branch_name>" if you want it on a branch)
west update

Now you have a new option in the GPS sample Kconfig. You can enable it by setting CONFIG_GPS_SAMPLE_NMEA_ONLY=y (note that it's default "n" /disabled at the bottom line of the sample's prj.conf). After setting the option, you can build and flash using the tool you prefer.
I'm attaching hex files for nRF9160 DK and Thingy:91:
gps_sample_nmea_nrf91dk.hex
gps_sample_nmea_thingy91.hex

In the log output, you'll see NMEA strings only.

You can share this log with us, and will see if we can see what's going on. Note that you can create a private ticket and share the files there if you prefer.

In some cases, we'll also need modem traces to know exactly what's going on.

Best regards,

Jan Tore

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

RicardoPereira — Tue, 16 Jun 2020 19:51:06 GMT

Hi Hucky,

Did you find the solution ? I'am having the same issue

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

RicardoPereira — Tue, 16 Jun 2020 19:11:27 GMT

Hi,

I'm having the same issues as jwhite with my thingy:91.

I can get up to 9 tracking but never get fix. I have the firmware 1.2.0.

Any ideas ?

Regards,

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

Øyvind — Wed, 10 Jun 2020 07:08:33 GMT

Hello jwhite,

What modem version are you running? Have you tested it outside in the open?

As stated in the nRF9160 DK documentation:
"GPS signals do not usually penetrate ceilings or other structures that well. Therefore, for best GPS performance, the DK should be placed on a flat surface in an open space outside, far from sources of interference and other structures that may block the signals from space."

If you are experiencing more issues, please register a new ticket regarding your issue.

Kind regards,
Øyvind

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

jwhite — Tue, 09 Jun 2020 18:02:13 GMT

I am having almost exactly the same issue, but with an out-of-the-box nRF9160DK running the GPS example with NCS v1.2. Since there is no verified answer here, I will present my question here. Here is my setup:

I received a nRF9160DK two weeks ago, and I was able to get it up and running with the Asset tracker firmware, and I was also able to get the GPS example working after flashing it from SES. After about 30-60 seconds, the gps example would get a fix and start printing out the nmea data on the nRF connect link monitor. I was able to get a fix indoors with the patch antenna provided.

But now, when I start up the nRF9160DK running the GPS example, it sits and prints out that it sees anywhere from 6-9 satellites, but it never finds a fix. I have let it sit for hours to no avail. I am not using the SUPL library because I want to run the GPS without LTE active. I've also tried going outside, switching from the onboard antenna to the external antenna, and restarting/re-programming the application. I seem to be stuck in the case that mlang said, but I never get out of it. Is there anything else I can try for this issue?

Here is a screenshot of the link monitor while the GPS example is running:

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

Øyvind — Wed, 12 Feb 2020 15:17:11 GMT

Hello phipi,

I will move this discussion to the private ticket you have registered, as that is where I will ask questions regarding your code.

To answer your last questions here, I have forwarded your questions to our nRF91 GPS expert, so far the issue leans towards software.

"The device never needs the almanac to get a fix, it should be able to do a cold start without any prior knowledge of anything whatsoever. The only thing the almanac would do in this case is to further speed up the TTFF by aiding which satellites to search for.

In this case, the device seems to be always able to find the satellites, but using 0 would be an indication that it cannot get the ephemerides and/or TOW downloaded from the satellites.

A log would indeed be helpful here. We can try to recreate the situation, but that will take 6-7 days for things to start happening if I understand correctly.

One way or another this is an SW issue somewhere. Since the device is able to get fixes, the HW seems to be fine. Since it is trying to get a fix every 6 hours, it is always cold starting, and as said, a cold start does not need any prior knowledge of anything.

But somehow the process of synchronization to the satellites seems to get corrupted and never finalized. It is useless to try to speculate here what could go wrong. If we don't get a log from the customer, I will have to forward this for recreation in our own lab. There is a good chance we would find nothing wrong => customer's logs needed anyway."

[quote userid="75356" url="~/f/nordic-q-a/56126/nrf9160-gps-tracking-satellites-but-can-t-get-fix"]Tracking: 8 Using: 0 Unhealthy: 0[/quote]

Have you tested our GPS sample alone? Do you get the same results? Have you tried your project on an nRF9160 DK?

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

phipi — Thu, 06 Feb 2020 16:55:09 GMT

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:

The device runs as expected with great (30~60s) TTFF
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)
On the next GPS fix attempt (6 hours later), once again it tracks many SVs and uses 0.
At this point we do a software reset
On the next GPS fix attempt (6 hours after software reset), the fix is successful (again with a very good TTFF)
After this the next few GPS attempts all time out
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?

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

Pema — Mon, 03 Feb 2020 07:02:23 GMT

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

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

Hucky — Wed, 29 Jan 2020 21:11:59 GMT

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.

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

Øyvind — Thu, 09 Jan 2020 08:33:04 GMT

Yes, please.

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

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

mlang3440 — Wed, 08 Jan 2020 20:39:22 GMT

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

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

Øyvind — Tue, 07 Jan 2020 08:42:45 GMT

Are you able to get a modem trace while it is failing to get a fix? This should help our R&D team see what is failing.

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

Øyvind — Mon, 06 Jan 2020 13:59:56 GMT

Hello,
I've been discussing your schematic with one of our HW engineers, and there is one potential issue: when the LTE radio is operating, the RF signal can intermodulate in the GPS LNA input stage and create unwanted harmonics. You should be safe either using an LNA with an integrated filter or by adding a filter on the input of the LNA.

Your design deviates from the reference design from the LNA vendor. You can also test with an external antenna. And please, test outside in open space.

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

phipi — Fri, 03 Jan 2020 18:43:57 GMT

Some more info about this:

It seems that on reset the GPS fix works every time but eventually gets into this state where it's tracking multiple SVs but not using any. If we reset when it's in that state it will get a fix on boot, but then return to the same fail mode on the next fix which happens several (4~ 6) hours later?

Is it possible that this is related to the modem clock? On boot we get the time from an NTP server (time.nrc.ca) which is the only item that we can identify as different from the fix that happens several hours after boot.

Is there anything we need to do to keep the modem time updated?

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

phipi — Fri, 03 Jan 2020 14:32:10 GMT

Hi Øyvind, we're using a yageo patch antenna (ANT1818B00AT1575S), and I've attached the relevant section of the design here.

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

Øyvind — Fri, 03 Jan 2020 10:31:29 GMT

Hello,

What GPS antenna do you have on your custom board? Can you provide any schematics? Are you outside or inside when testing?

Kind regards,
Øyvind