nrf9160: tracking time spent searching for LTE

Hi,

I’m experimenting with the nrf9160 LTE modem in poor network conditions. I would like to be able to keep track of how long the modem spends searching for LTE networks. I had assumed that we could do this by observing the registration status events emitted by the modem and tracking time spent in the LTE_LC_NW_REG_SEARCHING state but that appears to be insufficient.

Here are some timestamped logs I captured during testing, showing the values of the lte_lc_nw_reg_status events emitted from the modem:

00:01:42.464 Sleep exit: LTE_LC_MODEM_SLEEP_FLIGHT_MODE(4)
00:02:01.638 Reg status: LTE_LC_NW_REG_UNKNOWN (4)
00:03:27.269 Reg status: LTE_LC_NW_REG_SEARCHING (2)
00:03:29.888 RRC status: LTE_LC_RRC_MODE_CONNECTED (1)
00:03:30.947 Reg status: LTE_LC_NW_REG_REGISTERED_HOME (1)

From power measurement I can see that the modem begins LTE searching after the LTE_LC_NW_REG_UNKNOWN event, and it continues to search until 03:29 when it connects.

What can be inferred about the modem’s search behavior when we receive the LTE_LC_NW_REG_UNKNOWN event?

Why is modem searching not strictly associated with the LTE_LC_NW_REG_SEARCHING state?

Is there a correct approach to keeping track of time spent searching, either using these events or by some other means?

Thanks,

Robbie

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