The 4G LTE Cat-M1 band and the '5G' NB-IoT band being rolled out with mobile phone 5G bands are the bands the networks intend you to be using for machine-to-machine (M2M) products. They offer the basic level of service required for these products and in return the networks charge very little for using them.
NB-IoT is not accessible using mobile phone SIM cards; you need SIM a dedicated IoT to access them. These SIMs won't be connected to the Public Switched Telephone Networks (PSTN) so dial-to-open with your cheap PAYG SIM is not an option on these modern networks. You need infrastructure like the Priory Electronics iot-portal.com.
Vodafone are bringing NB-IoT to the UK and O2 are providing Cat-M1 LTE. Vodafone have good coverage across the UK now but O2's Cat-M1 coverage is still mainly in the South East.
In the picture above we have one of of our Dial-to-Open Keypad systems fitted with a BG95-M3 module which offers NB-IoT, CatM1 and good old 2G GPRS.
Let's see what networks are available here in Liverpool in June 2021!
at
OK
The 'at' command just shows us the module is running OK
ati
Quectel
BG95-M3
Revision: BG95M3LAR02A03
The ati command just identifies the module
at+creg?
+CREG: 0,5
AT+CREG check to see if we're on any networks... and yes we're registered and roaming on our chosen network.
Now for the interesting part. The AT+COPS=? command will show us all of the networks available to us:
at+cops=?
+cops: (1,"vodafone UK","voda UK","23415",9),(2,"vodafone UK","voda UK","23415",0),(1,"O2 - UK","O2 - UK","23410",0),(1,"EE","EE","23430",0),,(0,1,2,3,4),(0,1,2)
Let's go through them
1,"vodafone UK","voda UK","23415",9
1 - means 'Operator available', Vodafone UK is the network name, 23415 is the network ID and country code for UK and Vodafone... and 9 is the band in this case NB-IoT!
2,"vodafone UK","voda UK","23415",0
2 - means we're currently using this operator which is again Vodafone but this time the '0' at the end means we're only using 2G GPRS.
1,"O2 - UK","O2 - UK","23410",0
The above also shows 2G O2 is available...
1,"EE","EE","23430",0
...as is EE 2G.
at+csq
+csq: 17,99
The AT+CSQ command returns the received signal strength from the mast to us. In this case on 2G Vodafone we see it is 17 which is quite good for our office.
So that's a bit of a shame we're not on NB-IoT. We just registered on 2G first because it's a faster network. However, we can force it to go to NB-IoT with the COPS command as follows:
at+cops=4,1,voda UK,9
OK
...after a few seconds we use the AT+COPS? command to see which network we're on:
at+cops?
+cops: 1,1,"VF",9
Great! We're on NB-IoT. So what's the signal like?
at+csq
+csq: 31,99
31/31! Perfect. This is to be expected as if we're close enough to have a decent signal on 2G we're going to get a perfect signal on NB-IoT which is a low power network.