LTE B28 causes EC25EUX to remain in Search state and unable to connect

IoT Modules LTE Standard Module
1

Hi everyone,

Recently, I have been using the EC25EUX module with a Taiwan Mobile SIM card.
Taiwan Mobile supported 4G bands: FDD B1/3/7/8/28 (2100/1800/2600/900/700MHz)
Module firmware:
at+qgmr
EC25EUXGAR08A15M1G_20.200.20.200
I observed that after the module powers on, if AT+QNWINFO shows LTE BAND 28, the module cannot register on the network afterward. However, if it shows other bands, it can register successfully.

at+cfun=1,1
OK
AT+QNWINFO
+QNWINFO: “FDD LTE”,“46697”,“LTE BAND 28”,9560

OK
at+cops?
+COPS: 0

OK
at+cops?
+COPS: 0

OK
at+cops?
+COPS: 0

OK
at+cops?
+COPS: 0

at+creg?
+CREG: 0,2

OK
at+cereg?
+CEREG: 0,2

OK
at+qeng=“servingcell”
+QENG: “servingcell”,“SEARCH”

I did the following test again: I turned off B28, and the module immediately connected.

at+COPS?
+COPS: 0

OK
AT+QCFG=“BAND”
+QCFG: “band”,0x93,0x1a0080800c5,0x0

OK

AT+QCFG=“band”,93,1a0000800c5
OK
AT+COPS?
+COPS: 0,0,“TW Mobile”,7

OK
AT+QNWINFO
+QNWINFO: “FDD LTE”,“46697”,“LTE BAND 3”,1275

OK

I added B28 back again, and the module went back into Search mode, still not connecting to any other BAND.

AT+QCFG=“band”,93,1a0080800c5
OK

at+cfun=1,1
OK
AT+QNWINFO
+QNWINFO: No Service

OK
AT+COPS?
+COPS: 0

OK

at+QNWINFO
+QNWINFO: No Service

OK

If LTE band 28 cannot be used to register on the network, the module should use another available band to connect. Is this a bug in the module’s firmware?

Please help. Thank you.

2

Hi Vincent,

Thank you for reaching to us.

After checking the module specification, the EC25-EUX variant supports Band 28A, which is a sub-set of the full LTE Band 28.

In your test location, the Taiwan Mobile base station is broadcasting Band 28 (full band). When the module initially camps on this B28 cell, it can detect the signal but cannot complete network registration because the cell is outside the supported Band 28a range.

This explains why the module registers normally when it starts on other LTE bands but fails when the first serving cell is Band 28.

Thank you and have a nice day!

3

Hi YangShuan,

Thanks for your reply.

Because the EC25EUX is on several of our devices, as long as the customer uses a Taiwan Mobile SIM card, there is a chance that it will be completely stuck without registering the network due to B28. Based on my previous experience in using LTE modules, if it cannot complete network registration, the module should try to connect to other Bands and should not be stuck? Has the new version of firmware solved this problem?