Thuraya ARFCN

Johann T. johann.tzt at gmail.com
Thu Apr 30 12:52:18 UTC 2020


Dear all,

In the past weeks, I have been playing with the Osmocom GMR code. The code
has been successfully compiled and installed.

My intention is to listen to the broadcast channel of Thuraya in
the Netherlands. There are two spotbeams for NL namely 288 and 289. As I am
located at the border of the two beams, I have tried both options. So far I
couldn't see anything decoded in Wireshark.

I noted that the translation of ARFCN to frequency is slightly different in
the formula by Driessen (Practical cryptanalysis of the real world systems)
and in the ETSI standard (TS 101 376-5-5). There is a shift of half of the
channel bandwidth (31.25 kHz).

For your information, I am using Ubuntu 16.04, USRP B210, a wideband
antenna and LNA with about 20 dBi gain on L-band.

As mentioned by Sylvain in the mailing list, the gmr_multi_rx.py is
obsolete. I am using the gmr1_rx_sdr.py for my tests.

I ran the following commands (one each time) and with Wireshark listening
to lo interface while applying the gmr1.bcch filter.  Is this the right
approach as I don't see anything show up so far? Did I overlook something
here?

Spotbeam 289 (ARFCN 1007)
./gmr1_rx_sdr.py -s 10000000 -B L -f 1556484375 -a 1007 -g 45 (Driessen)
./gmr1_rx_sdr.py -s 10000000 -B L -f 1556468750 -a 1007 -g 45 (ETSI)

Spotbeam 288 (ARFCN 267)
./gmr1_rx_sdr.py -s 10000000 -B L -f 1533359375 -a 267 -g 45 (Driessen)
./gmr1_rx_sdr.py -s 10000000 -B L -f 1533343750 -a 267 -g 45 (ETSI)

Comments or suggestions are much appreciated. Many thanks in advance.

Best regards,
Johann
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