about cellular band selection: whole picture needed

[Kai]

Hi,

I've been testing the sample code at_clent with Verizon wireless. I can send AT command to the DK via nRF Connect "LTE Link Monitor".

Q1. run AT%XCBAND=? to print the list of supported bands, it shows "3 4 13 20". How does the modem know the list of supported bands -- are they defined in the SIM card?

Q2. run AT%XCBAND to print the current band, it shows "13". If there are more than one band available in the air, what makes the modem select one band over others?

Q3. run AT%XBANDLOCK=2,"1000" to lock the band 4, then run AT%XCBAND to print the current band, it still shows "13". why it doesn't show "4"?

Best,

Kai

[Martin Lesund]

Hi Kai,

Q1. These are defined in the modem firmware which is stored in the modem side of the SIP. 

So when more bands are getting certified then you will be able to update your modem firmware to support the new bands.

Q2. The modem will try to search through the different bands and will use the first one that is available.

Q3. If you are using the Bandlock command you need to set this before activating the modem (AT+CFUN=1). And the permanent mask is written to (modem) flash if you power off the modem with AT+CFUN=0.

Best Regards,

Martin L.

[stevenminnick]

Had a follow up question.  Every time I have connected I am on channel 13.  Verizon, USA in my area. 

Using the AT client code.  Powered up the board.  Link Monitor and did a board reset. 

AT%XCBAND
%XCBAND: 0
OK

So that means it's not connected (or still powered off).

AT%XCBAND=?
%XCBAND: (3,4,13,20)
OK

This should be the list of bands it supports.

AT%XBANDLOCK=2,"10000001000000000000"
OK
AT%XCBAND=?
%XCBAND: (13,20)
OK
AT%XBANDLOCK=2,"00000000000000001100"
OK
AT%XCBAND=?
%XCBAND: (3,4)
OK

This all looks normal.  (yes I know in the second XBANDLOCK I can leave off the leading 0's).  But then if I power on the radio I think that means it will only use bands 3 and 4.  Yes?

AT+CFUN=1
OK
AT%XCBAND=?
%XCBAND: (3,4)
OK

AT+CFUN?

(then lots of stuff happens)

Takes a long time to connect, longer than normal.  I expected not to have a connection at all, but then it did connect and then:

AT%XCBAND
%XCBAND: 13
OK

I thought I locked out band 13.

AT%XCBAND=?
%XCBAND: (3,4)
OK

Does it try the bands we specify and then when it fails on that does it go against the lockout and try them all just to make sure it's connected?