Fallouts in GNSS reception using AT#XGPS=1,1,1 and mobile networking disabled.

RE: Fallouts in GNSS reception using AT#XGPS=1,1,1 and mobile networking disabled.

Daniel B. J. — Tue, 09 Sep 2025 07:35:32 GMT

Thank you, I will try that.

Kind regards,

Daniel

RE: Fallouts in GNSS reception using AT#XGPS=1,1,1 and mobile networking disabled.

Håkon Alseth — Mon, 08 Sep 2025 14:15:44 GMT

Hi,

Ideally, we would want the NMEA strings to look at each individual satellite's output, and thus check the SNR.

This can be done by setting the log output mode in SLM:

Still, we can look at the "accuracy" parameter here based on the notified value we get back:

https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/applications/serial_lte_modem/doc/GNSS_AT_commands.html#unsolicited_notification

which will give us an indication on the overall accuracy of the returned GPS data.

This "accuracy" parameter is effectively a sum of "dilution of precision":

https://en.wikipedia.org/wiki/Dilution_of_precision_(navigation)

You want this number to be as low as possible. If we look at the numbers while driving, especially the ones where you have gaps, the accuracy parameter is 20 to 50 area:

(11:22:16.340) #XGPS: 55.841264,12.206062,68.760078,24.440924,22.152363,258.476349,"2025-08-21 09:22:16"
(11:23:51.330) #XGPS: 55.834678,12.174893,49.940460,45.608971,20.690598,272.305969,"2025-08-21 09:23:51"
..
(11:28:03.314) #XGPS: 55.835753,12.189951,48.109840,28.087284,14.759391,66.664894,"2025-08-21 09:28:03"
(11:28:35.326) #XGPS: 55.836433,12.197599,83.675026,48.383675,12.404172,63.467396,"2025-08-21 09:28:35"

This indicates that satellites are going from tracked->untracked, and the total amount of tracked satellites is less than 4.

[quote user=""]The driving test was done with the modem on the passenger seat, while driving through an area with mostly fields, single story houses, mild tree cover at some roads and no tunnels or bridges.[/quote]

I suspect that the placement of the device within the car has a great impact. The view it has present when in the seat is fairly limited towards the windshield itself, as compared to being placed in the windshield.

Note that newer cars have windows and windshields that can attenuate signals better than older cars.

I would need to look at the NMEA strings in both scenarios, especially the GPGSV, as this holds the SNR for each satellite in view, to confirm this theory.

Kind regards,

Håkon

RE: Fallouts in GNSS reception using AT#XGPS=1,1,1 and mobile networking disabled.

Daniel B. J. — Tue, 02 Sep 2025 10:03:44 GMT

Hello,

Sorry we are using AT firmware version 2.02 and nRF Connect SDK v5.2.0, but we used our external application MCU during these tests.

The setup in terms of AT commands looks like this:
AT
AT+CFUN=0 (changed to AT+CFUN=4 in newer implementation of our application firmware)
AT%XCONNSTAT=0
AT+CMEE=1
AT+CEREG=5
AT%MDMEV=1
AT+CESQ=1
AT+CEMODE=2
AT+CIND=1,1,1
AT+CSCON=1
AT+COPS=3,2
AT+CGEREP=1
AT%XPOFWARN=0,30
AT%XSYSTEMMODE=1,0,1,1
AT+CPSMS=0
AT+CEDRXS=0
AT+CGDCONT=0,"IP","APN"
AT%XCOEX0=1,1,1570,1580
AT%XMAGPIO=1,1,1,1,7,1574,1577
AT+CFUN=1

(wait for network registration)

AT#XNRFCLOUD=1

When this is recieved: #XNRFCLOUD: 1,0, we start the GNSS with: AT#XGPS=1,1,1

When the first valid GNSS position has been received we write AT+CFUN=20 in order to only look at GNSS performance.

I have the logs for the specific tests, but they where taken through our application MCU using YAT on windows 10. TX is from the application MCU, RX is from the nRF9151:

devzone.nordicsemi.com/.../nRF9151_5F00_GNSS_5F00_stationary_5F00_test_5F00_20250822_2D00_093956.log devzone.nordicsemi.com/.../nRF9151_5F00_GNSS_5F00_driving_5F00_test_5F00_20250821_2D00_110155.log

RE: Fallouts in GNSS reception using AT#XGPS=1,1,1 and mobile networking disabled.

Øyvind — Tue, 02 Sep 2025 09:31:45 GMT

Hello,

Can you please provide more information on what modem FW and version of nRF Connect SDK your are running on your device? An external antenna might improve the performance.

Are you able to provide some logs from your testing, and what settings are used?

Kind regards,
Øyvind