Roaming SIM, modem configuration and network attachement

[Kevin Barron]

We have purchased a radio fitted with the nRF9160 modem and fitted it with a roaming SIM for NB-IoT use, we are in UK and have Band 20 EE and Vodafone.

What are the initial radio AT commands used to select the MNO 

How is network selection determined?

In the event of a loss of an MNO. What thresholds are used to move the SIM to the 2nd MNO?

When a MNO is selected, on a power cycle, is that the 1st MNO checked therefore the radio should go back to previous MNO or does it rescan ?

[Syed Maysum Abbas Zaidi]

Hi,

Thanks for reaching out to us. Here are our response to your questions:

1. There is a +COPS command that can be set to select mobile network automatically or manually as mentioned here.

2. Network selection is governed by standard 3GPP rules (defined in 3GPP TS 23.122) as well as parameters configured on your SIM card. First modem try to attach to the last successfully registered PLMN and there are Preferred PLMN list as well like home PLMN, user-controlled and operator controlled preferred list which can effect the network selection during automatic procedure. For a roaming SIM, the operator controlled list is typically the key list, as it defines which visited networks (e.g. EE, Vodafone) are permitted and their priority. This list is programmed by the SIM provider.

3. I am not aware of specific exact signal thresholds (such as specific dBm levels for RSRP/RSRQ) that trigger an automatic switch from a lost MNO to a secondary roaming partner MNO (Can you tell exactly which thresholds are you referring, I can try to ask internally if needed). In general, in automatic mode, the modem will attempt to re-establish a connection with the lost network. If the connection fails permanently, the modem will perform periodic cell searches to find alternative available networks listed in your roaming SIM's profile. Whereas in manual mode, the modem will not automatically switch networks upon loss of service unless your application implements its own out-of-service recovery logic to release the lock.

4. Yes, upon a normal wakeup (such as from PSM) or power-up, the modem's priority is to avoid a full scan to optimize power. So it attempts to find and reconnect to the network that was serving the device before it went to sleep or was powered down.

Best Regards,
Syed Maysum

[Kevin Barron]

Hi Syed

Many thanks for the reply, that is very helpful in confirming my understanding, i have a few follow up questions:

3. when i worked in TETRA radio there were signal and quality thresholds which would trigger the device to look for an alternative radio carrier. If the thresholds were exceeded for a period of time the device would switch carriers. has the modem got such thresholds on which to operate? ie RSSI >100dBm + C/I >18dB for Xsecs would trigger a move. Is there anything like this in teh modem?

thanks.

Kevin

[Kevin Barron]

Hi Syed

Looking at the +COPs command, who programmes this , is it done by manufactuer?

The following command example selects the automatic network selection:

AT+COPS=0
OK