I’m working in a lab with a gNB for 5G. My UE is a Quectel module, the RM520N-GL. The 5G signal is on band 78. As it stands, my module cannot attach to the band-78 cell. I can try many times and it fails. To work around the problem I power down the gNB and restart it on band 77. Then I make the UE attach on band 77 without problems. Immediately afterwards I restart the gNB on band 78, and the UE is then able to attach to band 78 without issues. In other words, I first need to perform an attachment on band 77 and only after that can I attach on band 78.
Even when I run the same experiment with a different gNB (different software version, different antennas, etc.), the same problem occurs and I use the same workaround. So I suspect an issue in the UE. Two weeks ago none of this was happening; since last week I have been observing this odd behavior.
What should I investigate on my UE? Are there specific AT commands that could give me clues about the problem or even resolve it?
I’ve been analyzing this case over the past few days. When the modem fails to register on the 5G cell with band 78, the command AT+COPS=1,1,"00101" had previously failed. In other words, when the AT+COPS command fails, it returns nothing (there is no log message in this situation), and this implies that the modem will not be able to register on the cell. To work around this issue, I configure the modem to operate on band 77, and right after that the command AT+COPS=1,1,"00101" runs and returns a non-empty response. And this works even if there is no band 77 5G signal in the air. And to make it even stranger, right after that, when I configure the modem to operate with band 78 again, everything goes back to working normally. So I believe there might be some kind of bug in the modem. With this information, can you give me any advice?
Analyzing this case more deeply, I noticed the following behavior pattern:
AT+COPS=1,2,“00101” → works fine.
modem registers
AT+QPOWD=1 → modem powers off and automatically restarts
AT+COPS=1,2,“00101” → fails. No response
modem does not register
AT+QPOWD=1 → modem powers off and automatically restarts
AT+COPS=1,2,“00101” → works fine.
modem registers
AT+QPOWD=1 → modem powers off and automatically restarts
AT+COPS=1,2,“00101” → fails. No response
modem does not register
AT+QPOWD=1 → modem powers off and automatically restarts
AT+COPS=1,2,“00101” → works fine.
modem registers
AT+QPOWD=1 → modem powers off and automatically restarts
AT+COPS=1,2,“00101” → fails. No response
modem does not register
AT+QPOWD=1 → modem powers off and automatically restarts
In other words, the modem keeps alternating like this!!
What does this mean? What might I be doing wrong when using the modem??
Thank you very much for your attention. Best regards.
Dear @pimenta
After poweroff, do you check the status of SIM card? Or after register successfully, then execute AT+COPS=1,2,“00101”.
If no response, it means the operations was failed.