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.

[Kai]

Hi Martin

Permanent change can be made by command  AT%XBANDLOCK=1,"0100" followed by AT+CFUN=0, then followed by a reboot.

After reboot:

AT%XCBAND
%XCBAND: 0
OK
AT%XCBAND=?
%XCBAND: (3)
OK

 As expected, band-3 has been locked out, and the modem hasn't been started.

AT+CFUN?
...
AT+CFUN?
...

Lots of stuff happens.

AT%XCBAND=?
%XCBAND: (3)
OK
AT%XCBAND
%XCBAND: 13
OK

Band-3 is still locked out, however band-13 is the current one.

I did similar experiment to lock out band-20 only. The result is: band-13 is the current one.

I did similar experiment to lock out band-4 only. The result is: the current band is 0.

Pretty confused..

Best,

Kai

 

[stevenminnick]

Kai,

I think you have it backwards when you said:

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

 As expected, band-3 has been locked out, and the modem hasn't been started.

I believe the response to

AT%XCBAND=?

Is the list of bands it can support.  The AT command document says that XCBAND returns a list of supported bands.  I thought I remember seeing that out of the box this chip supports bands 3, 4, 13, and 20 and on mine when I did that I get:

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

Well the AT command document for %XBANDLOCK doesn't specifically say if a 0 or 1 locks out or locks in those bands.  Assuming the XCBAND command is right and it appears it is, then 0's in the BANDLOCK command locks out and 1 means locks in (or is supported).

I'm confused too.  The document isn't specific in it's language in the BANDLOCK section.   But when you run it, and check with XCBAND it appears that way. 

And based on my testing above, you can lock out or in any band and it uses whatever it wants anyway. 

I've done:

AT%XBANDLOCK=2,"1000000000000"
OK
AT%XCBAND=?
%XCBAND: (13)
OK

AT+CFUN?

(then lots of stuff happens)

AT%XCBAND
%XCBAND: 13
OK

And then I did

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

(then lots of stuff happens)

AT%XCBAND
%XCBAND: 13
OK

So I'm confused too.  Or I might have stumbled into a bug. 

[Kai]

hi, Steven

The following is the corrected statement:

Permanent change can be made by command  AT%XBANDLOCK=1,"0100" followed by AT+CFUN=0, then followed by a reboot.

After reboot:

AT%XCBAND
%XCBAND: 0
OK
AT%XCBAND=?
%XCBAND: (3)
OK

 As expected, band-3 has been locked in, and the modem hasn't started.

AT+CFUN?
...
AT+CFUN?
...

Lots of stuff happens, meaning the modem has started. Then,

AT%XCBAND=?
%XCBAND: (3)
OK
AT%XCBAND
%XCBAND: 13
OK

Band-3 is still locked in, I expected the current band is 3, but it is 13.

Then:

I did similar experiment to lock in band-20 only. The result is: the current band is 13.

I did similar experiment to lock in band-4 only. The result is: the current band is 0.

Best,

Kai