[srsran-users] srsue only working with --rat.eutra.dl_earfcn but not with --rat.eutra.dl_freq?

[Balthasar Indermuehle]

Dear all,

A quick background for my use case:

I've been using srsLTE since 2016 for base station detection at our remote
radio astronomy observatory in outback Western Australia. We normally don't
see any LTE stations there (which is what we want, hence the remoteness of
the site) but with tropospheric ducting the nearest cell 230km away becomes
decodable about 30% of nights in summer. I've been able to detect cells
from huge distances away, up to 900km. Ducting is an interesting phenomenon!

I've modified rrc.cc to extract and print PLMNID/TAC/CID and terminate upon
detection. Looking up that data with a location service allows geolocating
the towers.

The method by which I'm doing this is simple: use cell_search to find
active cells, then use my modified srsue to extract the MIB and SIB1 for
the aforementioned info.

Using the old srsLTE based srsue, I'd give it a downlink frequency to scan
as this parameter: --rf.dl_freq 778.0e6, also giving it an essentially
empty ue.conf file.

With the new srsue in srsRAN, it looks like this parameter has changed and
would now be substituted by --rat.eutra.dl_freq 778.0e6, again pointing at
an essentially empty ue.conf file (copied from the ue.conf.example but
commented the pre-set earfcn).

But, passing the new srsue the frequency as a parameter never decodes
anything. If, however, I'm passing the EARFCN like so:
--rat.eutra.dl_earfcn 46340 instead of the frequency, it works and decodes
the cell instantly.

yet, EARFCN 46340 corresponds to 778 MHz.

What am I missing? Do I need to specify additional parameters like a
frequency band identifier?

Thanks

Balthasar
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