Cannot get RSRP values of multiple nearby NB-IoT base stations anymore with newer modem firmware

[Thomas]

Hi,

I am trying to do geolocation using the NB-IoT chip on the nRF9160 DK. Therefore, I need the PCI and RSRP from multiple nearby base stations.

After enabling the radio (AT+CFUN=1), I successfully received this data by sending the AT%NBRGRSRP command on a device with modem firmware version 1.0: 

%NBRGRSRP: 11,6400,59,179,6400,56,40,6400,48,200,6400,47

(thanks to these posts: https://devzone.nordicsemi.com/f/nordic-q-a/53189/nrf9160-cell-tower-information-for-geolocation-with-lte-and-cell-tower-id-s-limited-nbrgrsrp and https://devzone.nordicsemi.com/f/nordic-q-a/42310/nrf9160-zephyr-ncs-zte-m-nb-iot-multiple-cell-tower-rssi )

However, I upgraded the modem firmware to version 1.1.1 and now the only response I get from the AT%NBRGRSRP command is "OK". I am not able to downgrade the firmware, since I also use GPS to evaluate the localization accuracy and some GPS commands were not available in the older firmware version.

Am I missing something to get the command back to work? Otherwise, is it possible to get the AT%NBRGRSRP command to work again on newer firmware versions?

Thanks in advance!

[Håkon Alseth]

Hi,

 

Here's a log where I get both no response and response (modem fw v1.1.1):

AT%NBRGRSRP
OK
AT%NBRGRSRP%NBRGRSRP: 106,6446,47,105,6446,41
OK
AT%NBRGRSRP%NBRGRSRP: 106,6446,47,105,6446,41
OK
AT%NBRGRSRP%NBRGRSRP: 106,6446,46,105,6446,40
OK
%CESQ: 43,2,21,3
AT%NBRGRSRP%NBRGRSRP: 106,6446,46,105,6446,41
OK
%CESQ: 43,2,26,3
AT%NBRGRSRP%NBRGRSRP: 106,6446,47,105,6446,41
OK
AT%NBRGRSRP%NBRGRSRP: 106,6446,47,105,6446,39
OK

 

The reason why I'm getting no response at first is because the UE is not actively searching for neighboring cells. It only does that if the RSRP drops below a defined level, communicated to the UE from the eNB during the attach process. This level is configurable in the eNB, therefore it differs between carriers.

As a test: If you hold your hand over the antenna for 20 seconds, then issue the AT command, you should see neighboring cells.

 

Kind regards,

Håkon

[Thomas]

Hi,

Thanks for the quick reply! May I ask how that threshold parameter is called? In that way, we can ask our provider to what value that parameter is set.

Also, wouldn't it be possible to ignore the threshold that the eNodeB communicates and always scan on the device for nearby base stations?

Kind regards,

Thomas  

[Håkon Alseth]

Hi Thomas,

 

Unfortunately, I do not have detailed knowledge about the procedure, but if you're interested in looking into this, check out "automatic neighbor relation".

 

Kind regards,

Håkon