More on GR-GSM

Getting a PCAP instead

Instead of reviewing the frames through wshark, you might prefer to use tshark. For th at you have two solutions: tcpdump

    tcpdump -i lo -w 0C.pcap &
    grgsm_decode ...
    pkill tcpdump && echo killed

or wshark - save as PCAPNG

    Save As...      $arfcn.0C.pcapng

as a result you can use handy filters from the command line

    tshark -r 0C7S.pcap -Y 'FILTER' -V
    #-2 -R 'FILTER'

Prepare to watch live

Either take the frequency from grgsm_scanner’s output, or install arfcncalc for convenience

    tar xf arfcncalc.tar
    cp arfcncalc/arfcncalc /usr/local/bin/
    arfcncalc -h


    freq=`arfcncalc -a $arfcn -d`


    arfcncalc -b GSM1800 -p
    freq=`arfcncalc -b GSM1800 -a $arfcn -d`

Watch Live

With auto-scroll enabled

    wireshark -k -Y '!icmp && gsmtap' -i lo &

    echo $arfcn
    echo ppm=$ppm

    grgsm_livemon_headless --help
    grgsm_livemon_headless --fc=$freq --gain=34 --ppm="$ppm" --args=rtl=0

    grgsm_livemon_headless --args=hackrf=0 --fc=$freq --gain=18 --samp-rate=2e6

sometimes I get better results with the GRC flavor (define Parameter fc=)

    gnuradio-companion grgsm_livemon_headless.grc

Can you see some 2bs already? But only one FDMA channel at a time (unless you manage to send to differe nt port to lo). The livemon only gets 0C.

Nothing comes out at 299e3. Next available sample rate setting is 901e3.