LTE-M/NB-IoT not registering with network after power cycle with PSM active

I have PSM enabled on a LTE-M/NB-IoT device (XB3-C-A2-UT-001) on Verizon network. The PSM mode seems to work correctly, and will reconnect to the cellular network when there is network traffic. However, if the system experiences a power loss while PSM is active, the radio does not reconnect to the cell network. I have let the device run for hours with no reconnection, I have tried enabling/disabling PSM flag in the DO field, and I have tried sleeping/waking using the different sleep and airplane modes.

Unfortunately, we can and must expect hard power-outages in our system. Thus, we cannot guarantee sufficient backup power to detect power loss and properly shutdown the cellular modem.

Are there any methods / procedures to force a reconnect of the radio to the network? How long should a reconnect event take (worst case) if we are powered down when PSM was active? Are there any other ideas or solutions that may help us recover from an unexpected power fault while using PSM?


What I would suggest is when this occurs, wait for two times your wake cycle. If you are not able to send/receive data, use the Shutdown command. When the radio is ready to power off, go ahead and cycle power on it.

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We were still using the default value for PU of 576000 s (or 6.6 days). We lowered PU to 7200s (2 hours), and we seem to be able to reattach within that window. That is, we haven’t had to wait for 2 full cycles yet for the radio to rejoin.

Thanks for the suggestion!