Don't register while doing a network search with +COPS=?

[klaasg]

Hi all,

We've been doing automatic network selection (+COPS=0) but are looking into moving to manual network selection.

When trying to search for available networks with +COPS=?, we see that the modem is already starting to connect to a network.

This seems not very wanted, especially if you read this:

When the modem is camped on a cell and properly registered, the manual search is done only in the current system. Scanning the other system would cause the modem to lose connection to the network, and it would not be able to receive paging from the network while scanning the other system.

https://devzone.nordicsemi.com/f/nordic-q-a/107865/at-cops-only-returning-nb-iot-networks-act-9-or-only-lte-m-networks-act-7
 

I know of a different modem that supports +COPS=2, meaning don't register do a network or deregister if you're on a network.

How would we properly go about listing all available networks and choosing one to connect to. If system mode is set to both LTE-M and NB-IoT, we want to see networks of both of those.

Thank you!

[dejans]

Hi,

Can you provide details about your use case?

What would be desired modem behavior in your case?

Best regards,
Dejan

[klaasg]

Hi.

In summary:

• We want to select a PLMN manually. We can do this with AT+COPS=1,2,"<PLMN>"
• To know what PLMNs are available, so we use AT+COPS=?. We need this because our devices travel to many countries.
• We see that the modem is registering on a network during the AT+COPS=? command. I think we don't want that because:
  • We might want to prefer a different network.
  • If it's connected on a NB-IoT network, it will not see LTE-M networks.

So our question is: can we search for available networks/PLMNs without registering on a network?

Thank you for your reply.

[dejans]

Hi,

Can you show your complete AT command sequence?

Best regards,
Dejan

[klaasg]

Our command sequence is:

// lte_lc_system_mode_set(LTE_LC_SYSTEM_MODE_LTEM_NBIOT, LTE_LC_SYSTEM_MODE_PREFER_NBIOT);

// turning on notifications
TX: AT+CSCON=1
RX: OK
TX: AT+CEREG=5
RX: OK
TX: AT%MDMEV=2
RX: OK
TX: AT+CGEREP=1
RX: OK

// starting search
TX: AT+CFUN=1
> Exit sleep
RX: OK
TX: AT+CFUN?
RX: +CFUN: 1
RX: OK
TX: AT+COPS=?

// all kinds on notifications
> LTE searching
> LTE cell changed: Cell ID: -1, LAC: -1
> LTE cell changed: Cell ID: 102623837, LAC: 19110
> Mode NB-IoT
> ECL 0
> RRC mode: Connected
RX: +CGEV: ME PDN ACT 0,0
> Event: Search done
> LTE registered roaming
> PSM update: TAU: 93600, Active time: 0
> RRC mode: Idle
> LTE cell changed: Cell ID: 102623836, LAC: 19110
> Enter PSM

// results
RX: +COPS: (1,"","","20601",9),(2,"","","20610",9),(1,"","","20620",9)

As you can see, the modem connects to an NB-IoT network and then the results of +COPS=? only include NB-IoT networks.