Getting frequency band in use

[Bjørn Mork]

Marius Kotsbak <marius at kotsbak.com> writes:
> 2014-05-05 23:56 GMT+02:00 Marius Kotsbak <marius at kotsbak.com>:
>> 2014-05-05 23:29 GMT+02:00 Dan Williams <dcbw at redhat.com>:
>>
>> On Mon, 2014-05-05 at 22:49 +0200, Marius Kotsbak wrote:
>>>
>> Hmm, when trying to do that, it then worked to connect... :/ Anyway, I
>> then get this using mmcli:
>>
>>    Bands    |      supported: 'cdma-bc15-aws, dcs, egsm, pcs, u2100, u900,
>> eutran-i, eutran-iii, eutran-vii, eutran-viii, eutran-xx'
>>            |        current: 'cdma-bc15-aws, dcs, egsm, pcs, u2100, u900,
>> eutran-i, eutran-iii, eutran-vii, eutran-viii, eutran-xx'
>>
>> Isn't that just listing all enabled bands, not what is currently in use?
>>
>
> Seems so. Anyway, that let me force use of the 800 MHz band, by setting
> bands to "eutran-xx". I saw that it gave better signal strength, but slower
> transfer speed, so the modem probably did a good choice by using higher
> frequencies in this case.

I believe the network decides the band and cell priority.  The modem
just obeys.  See for example
https://sites.google.com/site/lteencyclopedia/cell-reselection-procedures-in-lte#TOC-LTE-Cell-selection-and-reselection-
for a simple intro.

As for the speed, that's probably best explained by the channel
bandwidth (which is so much easier to watch looking at the Sierra
AT!GSTATUS command - we need something like this for generic QMI
devices).

I only have 10 MHz channels when using B20 (800 MHz): 

at!gstatus?                                                                             
!GSTATUS:                                                                               
Current Time:  10660            Temperature: 43                                         
Bootup Time:   70               Mode:        ONLINE         
System mode:   LTE              PS state:    Attached     
LTE band:      B20              LTE bw:      10 MHz  
LTE Rx chan:   6400             LTE Tx chan: 24400
EMM state:     Registered       Normal Service 
EMM connection:RRC Idle       

RSSI (dBm):    -59              Tx Power:    0
RSRP (dBm):    -84              TAC:         79E1 (31201)
RSRQ (dB):     -7               Cell ID:     010B7D05 (17530117)
SINR (dB):      5.6


OK

or B3 (1800 MHz aka the apple band :-):

at!gstatus?                                                                             
!GSTATUS: 
Current Time:  10928            Temperature: 44
Bootup Time:   70               Mode:        ONLINE         
System mode:   LTE              PS state:    Attached     
LTE band:      B3               LTE bw:      10 MHz  
LTE Rx chan:   1450             LTE Tx chan: 19450
EMM state:     Registered       Normal Service 
EMM connection:RRC Connected  

RSSI (dBm):    -59              Tx Power:    -4
RSRP (dBm):    -83              TAC:         79E1 (31201)
RSRQ (dB):     -8               Cell ID:     010CAA02 (17607170)
SINR (dB):     24.4


OK


compared the nice 20 MHz channel in B7 (2600 MHz):

at!gstatus?                                                                             
!GSTATUS: 
Current Time:  10786            Temperature: 42
Bootup Time:   70               Mode:        ONLINE         
System mode:   LTE              PS state:    Attached     
LTE band:      B7               LTE bw:      20 MHz  
LTE Rx chan:   3050             LTE Tx chan: 24400
EMM state:     Registered       Normal Service 
EMM connection:RRC Idle       

RSSI (dBm):    -77              Tx Power:    0
RSRP (dBm):    -103             TAC:         79E1 (31201)
RSRQ (dB):     -7               Cell ID:     0103B200 (17019392)
SINR (dB):     15.6


OK



Bjørn