RE: AGPS with SUPL vs NRF Cloud

Jan Tore Guggedal — Tue, 18 Aug 2020 11:19:19 GMT

Hi,

Glad to hear it worked out!

There's some more detail on (A-)GPS + LTE here that might be useful.

Best regards,

Jan Tore

RE: AGPS with SUPL vs NRF Cloud

pemar13 — Mon, 17 Aug 2020 13:34:21 GMT

Hi again!

Just as you suggested, I managed to get the A-GPS request in asset_tracker to work for Cat-M1 by setting CONFIG_MODEM_INFO_ADD_DATE_TIME=n!

Furthermore, today, the A-GPS response is handled and GPS tracking starts! I don't understand this, but I suspect that I am doing something differently.

I thus mark your answer as verified and will try to implement the PSM mode properly.I'll get back to you and your collegues when I'm stuck again.

Again, many thanks for your help!

/per

RE: AGPS with SUPL vs NRF Cloud

pemar13 — Mon, 17 Aug 2020 11:23:39 GMT

Hi Jan Tore!

Many thanks for the insights provided in your answers above! Especially what you write under B) is very good info for me as I haven't understood these (for me) intricate details until now.
The modem firmware version I use is 1.2.0 (sorry for not including this in my original ticket).

Providing you with modem traces will take some time depending on which priorities I have to make. I leave this ticket open for now, and will decide if it needs to be made private when I know how to proceed.

Thanks for now!

Besxt regards, Per

RE: AGPS with SUPL vs NRF Cloud

Jan Tore Guggedal — Mon, 17 Aug 2020 11:10:12 GMT

Hi Per,

Common for all the issues you're seeing is that they're hard to debug without knowing more about what the device sends to the SUPL server using LTE-M and to nRF Cloud in the asset tracker case. It would be very useful if you can follow the guide here and gather modem traces, which will help a lot in understanding what fails:

https://devzone.nordicsemi.com/nordic/cellular-iot-guides/b/getting-started-cellular/posts/how-to-get-modem-trace-using-trace-collector-in-nrf-connect

Also, I need to know which modem firmware version you're using.

Anyway, I'll try to answer your questions based on the information you've added here.

In the first log ouput you provide, this line says that gathering information for the A-GPS request fails:
<err> modem_info_params: Link data not obtained: 20 -5

Some networks/SIM cards don't provide all information that is requested, which can cause failures like this. I think you should be able to fix that issue by setting this configuration in your Kconfig:

CONFIG_MODEM_INFO_ADD_DATE_TIME=n

The GPS_EVT_OPERATION_(UN)BLOCKED events indicate whether the GPS is allowed to use the radio resources to receive GPS signals. By default, LTE has priority, which causes the GPS to be blocked from using the radio whenever the LTE modem requires it.

To use A-GPS, LTE has to be enabled while data is being transfered. When the download of A-GPS data is done, you can switch off LTE to let GPS operate. That's what's done in the GPS sample.

In the asset tracker a different approach is used, where the device instead Power Saving Mode (PSM) from the network, which, when granted, will let the GPS operate uninterrupted by LTE for the duration of the PSM interval, or until the device itself initiates a data transfer. The reason for this approach in the asset tracker is power consumption. Attaching to and detaching from network consumes relatively much power, compared to just let the modem go to sleep. In addition a TLS handshake would have to be done with the cloud server every time data is sent, and this is also a quite costly affair in terms of power consumption and bytes sent on air. It's not unusual that a TLS hanshake requires to send and receive 5k - 8k bytes. Staying in PSM and keeping the MQTT connection alive by periodic pings to the broker may therefore be preferred, depending on your use-case.

I would go for the seconds approach. There seems to be missing a line setting the system mode in the case where LTE should be activated, but other than that it looks reasonable.

The link controller library will soon also support activating GPS and/or LTE only, which will simplify this switching.

To sum up, I'd need modem traces and modem firmware version to continue. It will also be useful to know which network you are using. If you wish to share code or information that should not be public, you can make this ticket private.

Best regards,

Jan Tore