Thanks for all answers . I understand better now I'll test and let you know Pascal

Le mer. 8 juil. 2020 à 10:50, Sylvain Munaut 246tnt@gmail.com a écrit :

Hi,

...

this line is working fine

./gmr1_rx_sdr.py --args airspy -a 927 -s 6000000 -B L -f 1553968750 -g 19

...

-b 40 then after ./gmr1_rx 4 /tmp/arfcn_927.cfile wireshark is giving all informations

I have "immediate assignment on ARFCN 928 929 930 931

I tried to do the same with 928 929 930 931 ./gmr1_rx_sdr.py --args airspy -a 929 -s 6000000 -B L -f 1554031250 -g 25 -b 40 with 1 Gb of datas, I can retrieve only 2 frames in wireshark

I'm sure there is traffic on these 4 channels

So to follow assignments to dedicated channels, you need to use the `live` branch of the code and use gmr1_rv_live binary.

Basically you can't decode _just_ the traffic channel (i.e. the 928 929 930 931 ARFCNs). You need to first lock to the BCCH ( 927 ) and then follow the assignment so you have the proper alignment etc ... Which means you need to be receiving both channels at the same time, using multiple `-a` arguments to gmr1_rx_sdr.py

And then you use the gmr1_rx_live binary which supports processing several channels in parallel and feed it all the data at once using something like :

gmr1_rx_live 4 927:/tmp/arfcn_927.cfile 928:/tmp/arfcn_928.cfile ...

Each of the argument after the '4' (which is the sample-per-symbol) is in the form ARFCN:FILE where ARFCN is the ARFCN number and FILE is the path where to find the data corresponding to that ARFCN number.

And then the code will be able to find the BCCH lock to it and when it sees an assignement command, it will look if it has a data file available for that ARFCN and if it does, it will follow the assignement and start decoding the dedicated channel as well.

...

Is "immediate assignment " means TCH3 and voice ?

Not all Immediate Assignement means TCH3/voice, they can be control channels or packet data or whatever else ... it just means a phone was assigned a dedicated channel, you need to look at what type and what mode of channel it is to know what it's going to carry.

...

I tried all branches on git hub with same result

What is usage of gmr1_process_recording.py ? and arguments

So this script doesn't really "do" anything. All it does is take the filename of a file recorded by the osmocom_fft program (which uses a filename pattern that includes the center frequency and sample rate) and then it prints the commands you can use to process that recording. Mostly it's going to be two commands, the first one that will take the .cfile recording and split it into a bunch of ARFCN channels and then another command that will process all those ARFCN channels.

But as I said, it won't run those commands, it just prints them, you need to cut&paste them and run them and/or adapt them to your needs.

...

What is usage of gmr1_ambe_decode and gmr1_rach_gen

• gmr1_rach_gen generate examples RACH bursts, it's used for internal

testing of the c-band monitoring stuff in gnuradio

• gmr1_ambe_decode decodes TCH3 data payloads into PCM audio

Cheers,

 Sylvain Munaut

--

Hi,

On Wed, Jul 8, 2020 at 2:19 PM Andi Kita akita@qmail.qcc.edu wrote:

What sdr are you using?

I am trying to use usrp b200 and I was not able to make it work. I have read the research paper wrote by sylvain but that's for the old code.

Research paper ? I don't think I've ever written any of those ...

Is there anything or any other hardware that I could use? I have a b210 b200 bladerf x115 and a limesdr full board. I don't want to spend any money on the cube dongle and usrp1 are not made anymore.

All of the above should work fine. But you need a good RF setup. That means a good directional antenna with the right polarization, a good line of sight to the satellite and preferably external filters and LNA. Here I have so much out-of-band interference from terrestrial signals that without the cavity filter( http://shop.sysmocom.de/products/filter-rf-l-band ) the signals is very bad. I also use a minicircuit LNA with very high linearity ( ~ 200 mA bias current IIRC ).

Then you can use the same command line as he did, just remove the `--args airspy` and replace with `--args uhd` for instance for a USRP. (you might have to select the right antenna as well make sure the LED light up where you have your stuff connected).

Cheers,

Sylvain