Thingy:91 Asset Tracker V2 GNSS doesn't get a fix when connecting to a specific operator

[peng.cheng]

Hi,

Hope everything is fine with you!

There are three operators covering my workplace,

24007 tele2 --- PSM eDRX good ---
24008 Telenor --- PSM eDRX not supported ---
24001 telia --- PSM eDRX not supported ---

When I say `not supported`, I mean there is output `PSM parameter update: TAU: 3240, Active time: -1`.

I am working with GNSS recently, and found a strange issue,

when the thingy:91 connects to 24001, GNSS will fail to get a fix with a high possibility, around 3/4 GNSS location service fails,

but when thingy:91 connects to 24007, GNSS will always get fixes successfully.

At first, I think it could be that 24001 doesn't support PSM/eDRX, this will affect the GNSS because GNSS shares the same antenna with the LTE-M.

But then I found when thingy:91 connects to 24008, it still can get location fixes continuously and successfully.

I checked the paging time window by using `AT%XPTW?`, it is the same for both 24001 and 24008.

So my question is what is the key point to affect the GNSS function in this case for 24001 and 24008?

Any help will be much appreciated! Thanks!

BR,

Peng

[Øyvind]

Hello Peng, 

With what SIM card are you testing the connection? Are you able to provide the logs from Asset Tracker v2 along with modem traces? 

Thanks. 

Kind regards,
Øyvind

[peng.cheng]

Hi Øyvind ,

Thank you for your quick reply!

The SIM card is the iBASIS purchased together with the Thingy:91 board.

I tested in another place today, on top of an 8-floor building inside of the city. The situation is a bit different,

when the device connects to 24001, still no GNSS fixes, usually only 1 satellite is tracked.

when the device connects to 24007, several satellites are tracked, but still no GNSS fixes.

The attachments:

trace-2023-05-09T14-23-34.865Z_24001.bin is the trace log when the device connects to 24001,

trace-2023-05-09T14-27-11.143Z_24007.bin is the trace log when the device connects to 24007,

thingy91_24001_24007_all_fails_together_with_tracelog.txt is the application log with debug enabled, you can find `AT+COPS=1,2,"24007"`, this is the manual switch of the network.

BR,

Peng

thingy91_24001_24007_all_fails_together_with_tracelog.txt

trace-2023-05-09T14-23-34.865Z_24001.bin

trace-2023-05-09T14-27-11.143Z_24007.bin

[Øyvind]

Sorry, a small correction on the DK. This has a dedicated GNSS antenna (A2), which means there are two antennas on the DK while only one combined on the Thingy:91

 

[peng.cheng]

Hi Øyvind ,

Thank you for your reply!

If I am correct, for the nRF9160DK, I didn't set CONFIG_MODEM_ANTENNA_GNSS_EXTERNAL which means the board will not use an external GNSS antenna, it will use an onboard antenna instead, but in this case, the onboard antenna means A2 as shown in your left picture. This can explain why nRF9160DK works very well without an external GPS antenna.

I have two Thingy:91 boards, and both two boards have the same issue with getting a GNSS fix in Place 2 as I mentioned. So it is a very low possibility that both two boars are all broken.

The version of two Thingy:91 boards are:

1. 1.4.0 2020.22

2. 1.6.0 2022.49

Thank you!

BR,

Peng

[Øyvind]

peng.cheng said:

the onboard antenna means A2 as shown in your left picture. This can explain why nRF9160DK works very well without an external GPS antenna.

Yes, exactly. The Thingy:91 does a have an external connector J2 to connect external antenna. Please note: When an external antenna is used, the on-board Low-Noise Amplifier (LNA) should be disabled. The LNA enable signal is controlled by the COEX0 pin of the nRF9160, and its function is set by the AT%XCOEX0 AT command. The LNA makes the GPS receiver more sensitive to GPS signals and less sensitive to interference from other sources nearby.

From the Thingy:91 HW user guide

[peng.cheng]

Hi Øyvind,

Hope you had a nice weekend!

Now we are quite sure that the GNSS functions work well with an external GPS antenna.

But do you have any updates about why it doesn't work very well with the onboard NN03 antenna?

Or you just won't reproduce it?

Thanks!

BR,

Peng

[Øyvind]

Hi Peng, 

peng.cheng said:

Now we are quite sure that the GNSS functions work well with an external GPS antenna.

That is very good news!

peng.cheng said:

But do you have any updates about why it doesn't work very well with the onboard NN03 antenna?

No, unfortunately not. As I mentioned earlier, the antenna on the Thingy:91 is smaller than the one on the nRF9160DK. This can cause the signal level to be right on the edge of being usable, which again is boosted with a dedicated external antenna.

Our engineers had a look at the traces that you provided again, and based on location in modem traces and Google Maps they write the following answer:

The building is in W-E-direction and it blocks sky view to north - so low elevation SVs in northern sky are difficult to receive - but whole southern sky should be hearable.

There seems to be some sort of interference at the location, which is always difficult determine. The Thingy:91 is a prototyping platform, designed to be a proof of concept to work all around the world. In order to improve the antenna, you will need to design you own HW and provide an antenna that fits your needs. 

[peng.cheng]

OK, thank you Øyvind 

[Øyvind]

You're welcome!