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LTE_LC_NW_REG_SEARCHING and LTE_LC_MODEM_EVT_SEARCH_DONE

Achim Kraus

In order to get some more insights in energy consuming "network searches", I tried to keep track of the LTE_LC_NW_REG_SEARCHING and LTE_LC_MODEM_EVT_SEARCH_DONE events.

I get:

- LTE_LC_NW_REG_SEARCHING is mainly reported once at startup

- LTE_LC_MODEM_EVT_SEARCH_DONE seems to be reported on every PSM wakeup

According my question about some extra energy consumption nRF9160-DK - sometimes busy for 1 minute before entering PSM I would have expected, that one of the two helps to count such searchs, but for now, it's in vain.

Is there any other way then "measure the time to sleep" to count such "Higher Priority PLMN (HPPLMN) search"?

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  • 0

    Hi Achim,

    Need to inquire with our modem developer about the behaviour of HPPLMN.

    I will provide a reply later.

    Best regards,

    Charlie

  • +1 in reply to Charlie

    Hi Achim,

    Here is the explanation from our modem expert:

    1) I don't think there are any indications sent of the HPPLMN search. If higher priority PLMN is found, then there would be indications of selecting that PLMN. But no indications of the search itself.

    2) Not configurable by device or application. The configuration is at the SIM card and the device must obey that.

    Some overview about the High priority PLMN search. It's purpose is to ensure that device uses the highest priority network available. If device is already in home network (or it's equivalent) then there is no need for the HPPLMN search because the device is already at the highest priority network. On the other hand, when not in home network (i.e. device is roaming), then it is also in operators interests that the device uses the highest priority network available (based on SIM configuration). This is because depending on the subscription, higher roaming prices may be either operator's or customer's responsibility and the ordering of PLMNs configured to SIM card is typically done based on roaming agreements. Having this said, there is a exception: If application manually selects the network with AT+COPS, then HPPLMN searches are not done because the selected network could not be changed anyway due to the manual network selection mode. Downside in this approach is that if the manually selected network is not available at some point due to movement of the device, modem will keep searching only the manually selected network even though there would be other suitable networks available. Switching back to automatic network selection mode would help in this situation.

    Could you try the manually selected network method with your application?

    Best regards,

    Charlie

Reply
  • +1 in reply to Charlie

    Hi Achim,

    Here is the explanation from our modem expert:

    1) I don't think there are any indications sent of the HPPLMN search. If higher priority PLMN is found, then there would be indications of selecting that PLMN. But no indications of the search itself.

    2) Not configurable by device or application. The configuration is at the SIM card and the device must obey that.

    Some overview about the High priority PLMN search. It's purpose is to ensure that device uses the highest priority network available. If device is already in home network (or it's equivalent) then there is no need for the HPPLMN search because the device is already at the highest priority network. On the other hand, when not in home network (i.e. device is roaming), then it is also in operators interests that the device uses the highest priority network available (based on SIM configuration). This is because depending on the subscription, higher roaming prices may be either operator's or customer's responsibility and the ordering of PLMNs configured to SIM card is typically done based on roaming agreements. Having this said, there is a exception: If application manually selects the network with AT+COPS, then HPPLMN searches are not done because the selected network could not be changed anyway due to the manual network selection mode. Downside in this approach is that if the manually selected network is not available at some point due to movement of the device, modem will keep searching only the manually selected network even though there would be other suitable networks available. Switching back to automatic network selection mode would help in this situation.

    Could you try the manually selected network method with your application?

    Best regards,

    Charlie

Children
  • 0 in reply to Charlie

    Thanks for your answer.

    If it's possible to manually select network depends a lot on the use-case. Maybe that's more relevant for fixed device, for moving ones, maybe international moving ones, that may get difficult.

    I see two ways how to deal with that:

    - try to omit the extra energy (if possible)

    - try to measure (statistic), how often that happens

    I currently work more on the second approach.

    The questions are more to verify, that there is no easy way to make it better.

    So, again thanks for the answer. For now I measure the time from RRC idle to PSM sleeping and if that exceeds the active time, then I count that as HPPLMN search. It would be easier, it that would be reported. maybe in a future firmware version.

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