%XSYSTEMMODE with NB-IoT and LTE-M enabled (MFW1.3.x)

[lobaro-theo]

Hello,

if %XSYSTEMMODE is used with NB-IoT and LTE-M enabled plus no preference is set, e.g. "AT%XSYSTEMMODE=1,1,0,0" with MFW >= 1.3.0.

I have the following questions with this mode enabled:

• How is the network type selection implemented? Will the nRF9160 check for both and select the best? If so what type of metric is used for this?
• If a connection could be successfully established, when will we reassess for future connection trys whether the respective other technology would be better suited at the site in the meantime?

Thank you for the information of details in this matter.

Theo

[Sigurd]

Hi,

I have asked our modem firmware team about this. Will update the case when I have more information to share.

BR,

Sigurd

[Sigurd]

From the documentation we have: 0 – No preference. Initial system selection is based on history data and Universal Subscriber Identity Module (USIM).

More info from the modem team: There is no other criteria than just the fact that is the cell suitable or not. If a cell from preferred system is suitable based on 3GPP network/cell selection rules, then it is better than any cell in the secondary system. 

Modem will always search first for cell in the preferred system. If suitable cell found, then it stays there. If cell is not found, then the secondary system is searched. If suitable cell found from the secondary system, then modem will stay in the secondary system but periodically searches for suitable cells from the preferred system. The periodic is based on the higher priority PLMN search cycle specified by 3GPP. Operator can configure the mentioned period to SIM card but it is not configurable for user/application. And the final alternative is that no suitable cell can be found from either systems in which case modem will do periodic searches for both systems. Those searches (i.e. the periods) can be configured by client with AT%PERIODICSEARCHCONF.

[lobaro-theo]

Perfect, thank you.

[Umer Mahmood]

 Sigurd  In our application we recenlty changed implementation where we handled nbiot/ltm switching manually to using lte preference mechanisim offered by modem fmw 1.3.x. In general preference works as expected. But during testing in an emulated network envoirnment, our device never switched back to "prefered" system after it was connect to fallback system. 
Following was the test setup:

1. Set LTM as prefered network on modem.
2. Enable cell with nbiot.

3. After a while modem successfully connects to nbiot.

4. Enable basestation with ltm while nbiot network is still available.

5. At this point, both nbiot and ltm cells are available to the modem, but modem did not switch back to ltm atleast with 10 to 15 minutes. 

Please let me know if I need to open a seperate ticket for this. 

[Sigurd]

Hi Umer,

Umer Mahmood said:

Please let me know if I need to open a seperate ticket for this. 

Yes, please open a new ticket for this.