nrf9160 radio access: LTE vs GNSS

RE: nrf9160 radio access: LTE vs GNSS

Øyvind — Fri, 17 Nov 2023 13:14:23 GMT

Sounds good! Please test and let us know how that works!

Kind regards,
Øyvind

RE: nrf9160 radio access: LTE vs GNSS

shamilton — Thu, 16 Nov 2023 21:01:40 GMT

Hi Øyvind,

Thanks for the response. Due to the 12 second preferred time window, we will probably have our minimum upload rate be 15 seconds. We appreciate the team looking into this for us.

Regards,

Stuart

RE: nrf9160 radio access: LTE vs GNSS

Øyvind — Thu, 16 Nov 2023 12:22:16 GMT

Stuart, my sincere apologies for the late reply. Our modem team had a look at the logs and provided the following response:

The reason why the RRC connection activation sometimes gets delayed is a 12 second preferred time window granted to GNSS. During a preferred time window, GNSS blocks LTE. When the GNSS preferred time window ends, the RRC connection activation starts immediately.

This is as per design and there’s currently no way around it. GNSS can only get a preferred time window right after the RRC connection release. Because of this the delay is not visible with the longer upload cycle, because the preferred time window has already ended before the next upload.

Kind regards,
Øyvind

RE: nrf9160 radio access: LTE vs GNSS

Øyvind — Thu, 02 Nov 2023 13:03:15 GMT

Thanks Stuart! I have forwarded this to our modem team and hope to have an answer by tomorrow or Monday.

Kind regards,
Øyvind

RE: nrf9160 radio access: LTE vs GNSS

shamilton — Tue, 31 Oct 2023 20:11:20 GMT

Hello, I am a colleague of amessner at the same company. Sorry for the wait, but we managed to capture a modem trace which highlights the delay in switching from RRC idle to RRC connected. Attached is the modem trace from a test, the application log associated with the same test, and a pdf document that annotates the application log to help explain what is happening. In the test, we managed to capture examples of both normal functionality, and when there are delays in the transition to RRC connected.

We hope the modem trace will help you to understand what might be causing these delays

Please let us know if there is any other info we can provide.

Thanks,

Stuart

devzone.nordicsemi.com/.../trace_2D00_2023_2D00_10_2D00_30T21_2D00_37_2D00_01.203Z.bin

RE: nrf9160 radio access: LTE vs GNSS

Øyvind — Thu, 26 Oct 2023 11:53:36 GMT

Hello,

[quote user="amessner"]I'm planning to collect a modem trace later this week[/quote]

Any update on this?

Kind regards,
Øyvind

RE: nrf9160 radio access: LTE vs GNSS

Johnny Nguyen — Fri, 20 Oct 2023 17:27:59 GMT

[quote user="amessner"]This is a theoretical question that you should be able to answer without a modem trace. Are there any possible scenarios where GNSS would report to be blocked by LTE if the modem is in RRC idle?[/quote]

Our developers state there are some LTE operations which can block GNSS also when an RRC connection is not active. For example, during cell search LTE uses the RF and GNSS needs to be blocked.

RE: nrf9160 radio access: LTE vs GNSS

Øyvind — Tue, 17 Oct 2023 12:43:26 GMT

Alex, understood. Thanks for providing details so far. I've forwarded your question to our team and hope they can provide an elaborate answer to your use case.

Kind regards,
Øyvind

RE: nrf9160 radio access: LTE vs GNSS

amessner — Mon, 16 Oct 2023 14:58:39 GMT

[quote userid="77062" url="~/f/nordic-q-a/104598/nrf9160-radio-access-lte-vs-gnss/450595"]In order for us to see if there is an issue with RRC and RAI, we will need a modem trace from the device in field.[/quote]

I'm planning to collect a modem trace later this week

[quote userid="77062" url="~/f/nordic-q-a/104598/nrf9160-radio-access-lte-vs-gnss/450595"]Is there a reason for why you want to have such a high upload cycle? [/quote]

I understand that this use case is not what the nRF9160 is intended for, but I'm running experiments to evaluate feasibility of product use case given by my management.

[quote userid="77062" url="~/f/nordic-q-a/104598/nrf9160-radio-access-lte-vs-gnss/450595"]The same goes for this issue with regards to modem trace. Have not heard about this issue before. [/quote]

This is a theoretical question that you should be able to answer without a modem trace. Are there any possible scenarios where GNSS would report to be blocked by LTE if the modem is in RRC idle?

Thanks

Alex

RE: nrf9160 radio access: LTE vs GNSS

Øyvind — Mon, 16 Oct 2023 13:34:02 GMT

[quote user="amessner"] Is this the cell tower/network not switching us to RRC connected sooner and I am missing something in regards to the LTE protocol or is there some process in the modem that adds this delay of 5s?[/quote]

In order for us to see if there is an issue with RRC and RAI, we will need a modem trace from the device in field. Is there a reason for why you want to have such a high upload cycle?

[quote user="amessner"]QUESTION #2: The second question is more generic and not directly related to the use case described above. My assumption is that if the modem reports to be in RRC idle, then the GNSS can always access the radio and track satellites and is never blocked by LTE. However, I have seen scenarios where the GNSS flag "NRF_MODEM_GNSS_PVT_FLAG_DEADLINE_MISSED" is set even with the modem in RRC idle. Is my assumption wrong? If yes, then what causes the modem to block GNSS even if the modem is in RRC idle?[/quote]

The same goes for this issue with regards to modem trace. Have not heard about this issue before.

Thanks.

KInd regards,
Øyvind

RE: nrf9160 radio access: LTE vs GNSS

amessner — Thu, 12 Oct 2023 15:18:21 GMT

Hi Øyvind,

GNSS is running in continuous mode, LTE (NB-IoT) is enabled at all times. GNSS tracking should be active any time the radio is not used for the upload cycle.

Periodically we upload data, the upload rate is configurable. During an upload the modem transitions from RRC idle to RRC connected, uploads the data and transitions back to RRC idle. The transition from RRC connected back to RRC idle would usually take 5s (with our local network), but we use AS-RAI to immediately transition back to RRC idle, this reduced the time for the complete RRC connected session to a ~3 seconds.

Here is a specific scenario of a upload cycle of 15s:
- The first ~3 second the LTE link is used to upload data (RRC connected session)
- The remaining ~12 seconds the GNSS accesses the radio to track satellites

This works fine, however when we increase the upload cycle to run every 6s then it sometimes works and sometimes doesn't:
When running the upload cycle every15s upon opening a socket and sending some data the modem always transitions immediately from RRC idle to RRC connected, however with an upload cycle every 6s we sometimes see a delay of ~5s before the modem switches to RRC connected to send the data (with sometimes I mean hours at a time).
QUESTION #1: Is this the cell tower/network not switching us to RRC connected sooner and I am missing something in regards to the LTE protocol or is there some process in the modem that adds this delay of 5s?

QUESTION #2: The second question is more generic and not directly related to the use case described above. My assumption is that if the modem reports to be in RRC idle, then the GNSS can always access the radio and track satellites and is never blocked by LTE. However, I have seen scenarios where the GNSS flag "NRF_MODEM_GNSS_PVT_FLAG_DEADLINE_MISSED" is set even with the modem in RRC idle. Is my assumption wrong? If yes, then what causes the modem to block GNSS even if the modem is in RRC idle?

I will try to collect modem traces to support question #1 and attach them here.

Thank you

Alex

RE: nrf9160 radio access: LTE vs GNSS

Øyvind — Thu, 12 Oct 2023 07:58:38 GMT

Hi Alex,

Could you provide more details on your issue? Do you have any application logs and/or modem traces that you can provide us with?

Remember that operation is time multiplexed with LTE modem, and it is possible to use the GPS and QZSS receiver to obtain position either while the LTE is in RRC Idle mode or power saving mode (PSM), or when the LTE modem is completely deactivated.

How long does the GNSS run vs LTE modem?

Thanks.

Kind regards,
Øyvind