Hi!
We are developing a board with nRF9160 and want to use it on NB-IoT mode.
The development is made in Romania, Cluj-Napoca and here we have no problem with it. Even at -120 dBm we can connect to the network and change data with our UK server. Here we usually have -80 dBm inside the building and everything works just fine. We use a Vodafone UK SIM in Romania with the roamin enabled.
When we try to use the same hardware and software in UK things start changing. Inside the building (in central London), it never connects to the network. Outside things are better, but only when we have a straight line to the signal towers. But when this happen RSSI is very good, like -54 dBm. It is a strange behavior because for example, once we had -65 dBm near a building, but when we cross the corner it disconnected and never connected again in that spot, like the building absorbed all the signal from the cellular tower. The same behavior resulted when tested in Liverpool.
I should tell that Vodafone Romania used B20 for NB-IoT and Vodafone UK use B8 and B20 for NB-IoT according with this website https://halberdbastion.com/technology/iot/iot-protocols/nb-iot-lte-cat-nb1.
Also I will post few AT commands and the answers here just to clarify some things.
SENT: AT%XCBAND=?
%XCBAND: (1,2,3,4,5,8,12,13,17,19,20,25,26,28,66)
SENT: AT%XDATAPRFL?
%XDATAPRFL: 4
SENT: AT%XSYSTEMMODE?
%XSYSTEMMODE: 0,1,0,0
Vodefone UK recommended us to enable deep search using AT%XDEEPSEARCH=1, but with no changes (I don't understand exactly if we should enable it or not). Also they told us to search for neighbor networks using AT%NBRGRSRP, but from what I see this works only after a connection with the tower was established and we can't connect. Also when calling AT%COPS=? and the network mode is set to NB-IoT we get no results, or maybe sometime +CEREG: 2,"FFFE","FFFFFFFF",9,0,0,"11100000","11100000" is returned. When I send this command (AT%COPS=?) in Romania even without the SIM, it finds Vodafone. If we change to LTE-M in London and use AT%COPS=? a network is returned which I think is O2, but not sure because we are interested mainly on NB-IoT.
The hardware was reviewed by an engineer on DevZone and he found no problem. And we tested this with few external antennas and one chip antenna with the same results. Also nRF9160 DK is unable to connect to network when using the AT firmware and last modem firmware.
I hope we are setting something bad otherwise we should change the chip and this will cost us a lot because we already developed the code for this in Romania where everything worked fine, but the client is from UK.
Today I will test the board in different places in Cluj-Napoca just to eliminate the possibility that our office is placed very favorable and I will write a comment here if something is getting bad in Romania too.
Is there anyone that had the same problem? We done a lots of tests and we found nothing.
Thank you!
