NRF9160 - LTE-M takes a long time for first connection

RE: NRF9160 - LTE-M takes a long time for first connection

fernan — Fri, 23 Feb 2024 07:24:05 GMT

Hi everyone,

At this moment I have the same problem, but in the past, I had not.

About one year ago, the connection spent about 3 seconds. Now it is very difficult to connect and register. The time to connect is too high.

Eneko, have you solve it?

I am doing test in Spain too, with Orange and Emnify SIMs, but with the same result.

RE: NRF9160 - LTE-M takes a long time for first connection

Didrik Rokhaug — Tue, 21 Nov 2023 14:47:46 GMT

[quote user="Eneko Montero"] is there any data about the last PLMN saved in the modem? [/quote]

Yes, the modem will save information about the connected network. First in RAM, but it will eventually be stored in flash as well. The application can also trigger the modem to store the information in flash with AT+CFUN=0 (note that this will turn the modem off, not just write the information to flash).

[quote user="Eneko Montero"]What does initial network search means in this case? Using a new, unused SIM card?[/quote]

By initial network search, I meant when the modem is searching for a network when it is not already connected to a network.

[quote user="Eneko Montero"]I can reduce the time (locking bands) the modem takes to register with a new SIM card (then unlock bands).[/quote]

Correct.

[quote user="Eneko Montero"]As far as I understood, it will start searching the HPLMN (global) and then the Prefered PLMN (26201). After that try to register in nearby networks. Same procedure as the initial network search. Am I right?[/quote]

Yes. Though the modem will only search for networks potentially deployed in the country it is in. As the home PLMN is global, it can potentially be found anywhere, so the modem will always search for it. However, it will only search for 26201 if it is in Germany.

RE: NRF9160 - LTE-M takes a long time for first connection

Eneko — Tue, 21 Nov 2023 11:56:01 GMT

Hi Didrik,

Thank you so much for the explanation. Now I understand better what is going on.

As you said, it seems the %XCOUNTRYDATA won't help.

[quote userid="81181" url="~/f/nordic-q-a/105091/nrf9160---lte-m-takes-a-long-time-for-first-connection/456532"]1nce log show that the SIM card does not contain EF_EPSLOCI file, thus the home network (HPLMN) must be searched first. The HPLMN was not found and the only preferred PLMN configured to the SIM card was not either found (262 01). The only option left for modem is to try to Attach to some random network with high quality signal (3 of them were found). At first modem tries to Attach to 214 01 and luckily the Attach succeeds immediately.[/quote]

Although the SIM does not have EF_EPSLOCI file, is there any data about the last PLMN saved in the modem? It seems so, since after initial registration the modem takes less than 10s to connect.

[quote userid="81181" url="~/f/nordic-q-a/105091/nrf9160---lte-m-takes-a-long-time-for-first-connection/456532"]Unfortunately, the fix introduced in mfw 1.3.5 doesn't impact the initial network search. However, it does mean that the modem will not search for the home network unless it is connected to a different global PLMN.[/quote]

What does initial network search means in this case? Using a new, unused SIM card?

I can reduce the time (locking bands) the modem takes to register with a new SIM card (then unlock bands). This way the modem have data about a PLMN -correct me if I'm wrong-.

What happens if the modem can't register to the last PLMN? eg: different country (MCC change) or area (same MCC but MNC/operator not available in that area).

As far as I understood, it will start searching the HPLMN (global) and then the Prefered PLMN (26201). After that try to register in nearby networks. Same procedure as the initial network search. Am I right?

Thank you for your help.

Best regards.

RE: NRF9160 - LTE-M takes a long time for first connection

Didrik Rokhaug — Mon, 20 Nov 2023 18:09:52 GMT

Yes, and sorry for this taking a bit longer than expected. There were some additional details I had to check.

First of all, the modem team pointed out that, in general, swapping the SIM cards does not simulate scenario where a new SIM card is used for the first time. Typically SIM card contains the last registered PLMN in EF_EPSLOCI file, so when such card is inserted to whatever device, the last registered PLMN will be searched first. In addition, factory reset would be needed for clearing the cell history modem has stored earlier.

As for why the 1nce SIM card takes longer to connect to a network, this is what the modem team said:

1nce log show that the SIM card does not contain EF_EPSLOCI file, thus the home network (HPLMN) must be searched first. The HPLMN was not found and the only preferred PLMN configured to the SIM card was not either found (262 01). The only option left for modem is to try to Attach to some random network with high quality signal (3 of them were found). At first modem tries to Attach to 214 01 and luckily the Attach succeeds immediately.

They also commented on the use of %XCOUNTRYDATA:

In general, for devices that travel a lot we recommend to use the %XCOUNTRYDATA which can be used for prioritizing certain bands and channels in certain countries. This is very useful if preferred networks for many different countries have been configured to the SIM card. So for example, 1nce SIM card had 262 01 configured as preferred network. If certain band had been configured with %XCOUNTRYDATA for MCC 262, that band would have been scanned first when in country with MCC 262 resulting typically much faster Attach. Unfortunately, 1nce card didn’t have more than one preferred network configured, so benefit of using %XCOUNTRYDATA would limited to country with MCC 262 only.

[quote user="Eneko Montero"]I updated the modem firmware to v1.3.5 as the modem won't search for PLMN started with 901.[/quote]

Unfortunately, the fix introduced in mfw 1.3.5 doesn't impact the initial network search. However, it does mean that the modem will not search for the home network unless it is connected to a different global PLMN.

RE: NRF9160 - LTE-M takes a long time for first connection

Eneko — Fri, 17 Nov 2023 15:41:13 GMT

Hi Didrik, any feedback from the modem team?

Best regards.

RE: NRF9160 - LTE-M takes a long time for first connection

Didrik Rokhaug — Tue, 14 Nov 2023 13:03:58 GMT

Thanks.

I have forwarded the trace to our modem team, so they can take a look at it.

They typically answer quite quickly, so I should have an answer within a day or two.

RE: NRF9160 - LTE-M takes a long time for first connection

Eneko — Fri, 10 Nov 2023 09:01:39 GMT

Hi Didrik,

Attached the modem trace:

devzone.nordicsemi.com/.../1nce_5F00_modem_5F00_trace.bin

Best regards.

RE: NRF9160 - LTE-M takes a long time for first connection

Didrik Rokhaug — Thu, 09 Nov 2023 15:56:36 GMT

Sorry for the late response.

There might be other reasons for why the 1once SIM takes longer to connect to a network than just the time it takes to search for it.

Could you take a modem trace, so we can look at what happens on the modem and SIM side?

RE: NRF9160 - LTE-M takes a long time for first connection

Eneko — Tue, 07 Nov 2023 11:12:31 GMT

Hi Didrik,

Have you been able to look at this?

Best regards!

RE: NRF9160 - LTE-M takes a long time for first connection

Eneko — Thu, 02 Nov 2023 15:35:43 GMT

Hi Dridik,

Thank you so much for the explanation.

I updated the modem firmware to v1.3.5 as the modem won't search for PLMN started with 901.

See mfw_nrf9160_1.3.5_release_notes.txt:

- Fix for higher priority PLMN search. Global PLMN IDs (start with digit 9) are no more
automatically considered to be suitable for higher priority PLMN search and selection.

I'm using an iBasis SIM for comparation. For emulate the first connection I'm switching both SIMs to see the time. The iBasis SIM takes less than 20s to make the first connection.

But with 1nce SIM don't see any improvement. It takes the same time (around 1:20 min) to connect using automatic network selection (+COPS=0).

The second connection (resetting the MCU) takes almost no time with both SIM cards.

If I change to 1nce SIM after connecting using iBasis it takes again 1:20 mins even if it's connecting to the same PLMN used by iBasis SIM.

Could this behaviour mean the modem is still trying to connect to the Global home network (901)?

Thank you for your help.

Best regards.

RE: NRF9160 - LTE-M takes a long time for first connection

Didrik Rokhaug — Tue, 31 Oct 2023 15:12:35 GMT

[quote user="Eneko Montero"]I've been trying different configurations to improve the connection time. It seems using the XBANDLOCK command and locking bands 3 and 20 (used here in Spain) the time improves a lot, from more than 1 min to less than 30 seconds. I thought XBANDLOCK command and XCOUNTRYDATA command did the same: lock the search to the given bands. Am I missing something?[/quote]

%XBANDLOCK limits what bands the nRF9160 will use. The fewer bands that are enabled, the fewer bands it will have to search through, and the faster a suitable network will be found.

%XCOUNTRYDATA on the other, simply changes the priority in which the enabled bands are searched through. It doesn't restrict which bands can be used. However, much of the network search process is also controlled by the LTE specification, so e.g. in this case, where the home network of the SIM card is a "global" network, the modem will have to search for that network first. If the SIM card had had a different home network, you would probably have seen a bigger improvement.

[quote user="Eneko Montero"]Regarding the modem trace I'm not sure I understand the proccess. As far as I know I need 2 UART, one for the AT commands and another one for the trace. But our custom board only has one UART (UART0). Can I get the trace with only one UART?[/quote]

You only need one UART to take a modem trace. With an extra one, the Cellular Monitor is able to send some At commands to make sure that some information is available in the trace (and so that the Cellular Monitor is able to read the information out of the trace), but it is not strictly necessary.

One other detail to be aware of, is that unless you are using NCS v2.5.0 which just released, the UART modem trace backend is hardcoded to use UART1. It works with the other UART instances as well, you will just have to change the code manually. Or, you can change the pins, so that UART1 uses the pins you usually use for UART0.

Another option is to capture the trace over RTT instead. That way, you don't need to make any changes to how you use the peripherals of the nRF9160.

But, with the home network of the SIM card being a "global" network, I doubt a modem trace will give us much more information.

RE: NRF9160 - LTE-M takes a long time for first connection

Eneko — Tue, 31 Oct 2023 12:35:03 GMT

Hi Didrik,

I'm using a 1nce SIM card. The MCC is 901 which according to 1nce information is "Worldwide Shared Mobile Country Code" (see this link).

Regarding the modem trace I'm not sure I understand the proccess. As far as I know I need 2 UART, one for the AT commands and another one for the trace. But our custom board only has one UART (UART0). Can I get the trace with only one UART?

I've been trying different configurations to improve the connection time. It seems using the XBANDLOCK command and locking bands 3 and 20 (used here in Spain) the time improves a lot, from more than 1 min to less than 30 seconds. I thought XBANDLOCK command and XCOUNTRYDATA command did the same: lock the search to the given bands. Am I missing something?

Best regards.

RE: NRF9160 - LTE-M takes a long time for first connection

Didrik Rokhaug — Mon, 30 Oct 2023 13:19:32 GMT

What SIM card are you using?

How effective the use of %XCOUNTRYDATA is depends a lot on what SIM card you are using, and what networks the SIM card tells the modem to search for.

One thing you can check is the first 5 or 6 digits of the IMSI (or is it a multi-IMSI SIM?), which tells you the home network of the SIM card, i.e. the network that the SIM card most wants to be connected to. The first 3 digits are the MCC, which represents the country, while the next 2 (European standard) or 3 (North American standard) represents the operator.

A modem trace will also help show what the modem is doing while it is searching.

RE: NRF9160 - LTE-M takes a long time for first connection

Eneko — Fri, 27 Oct 2023 15:49:26 GMT

Hi Didrik,

I have been doing some connection tests with this command but unfortunately I haven't seen any difference between using it or not.

If I don't use any commands and let the device connect to it's own to the network, it takes aproximately 1 minute and 25 seconds.

Using this series of commands (I'm doing test in Spain) it takes 1 minute 20 seconds to connect:

AT

OK

AT%XCOUNTRYDATA=1,"4,214,3,1207,20,6175"

OK

AT+CFUN=1

OK

So I'm not really seing a difference. I'm I doing something wrong? I'm I missing an intermediate command?

Best regards

RE: NRF9160 - LTE-M takes a long time for first connection

Didrik Rokhaug — Thu, 26 Oct 2023 14:49:16 GMT

[quote user="Eneko Montero"]Unfortunately, the devices travel all around the world so we cannot know in which country the device is in when it’s trying to connect. [/quote]

The %XCOUNTRYDATA command doesn't lock the device to a single country. Instead, when the device detects that it is in a country with information from %XCOUNTRYDATA, it will search the bands set with the command first.

You can provide information for up to 70 countries, so you should be able to cover the most likely countries.

RE: NRF9160 - LTE-M takes a long time for first connection

Eneko — Thu, 26 Oct 2023 14:28:31 GMT

Hi! Thank you for your quick reply. Unfortunately, the devices travel all around the world so we cannot know in which country the device is in when it’s trying to connect.

Is there any other thing we can do to help the modem connect that first time?

Best regards

RE: NRF9160 - LTE-M takes a long time for first connection

Didrik Rokhaug — Thu, 26 Oct 2023 13:25:53 GMT

Hi,

Yes, the initial connection with a new SIM card/in a new location might take a long time.

One thing you can try, is to use the %XCOUNTRYDATA AT command to give the modem a bit more information about what bands it should search first in the given country.

However, much of the cell and network selection procedure is controlled by the LTE spec., so there isn't much that can be done.

[quote user=""]Why does the first connection take a long time and the rest doesn’t?[/quote]

The modem will store information about the connected network (in flash if you disconenct with AT+CFUN=0), and use this information when re-connecting to the network.

That way, it knows what network to search for, and where to find it, and it doesn't have to try other networks first.

Best regards,

Didrik