Sniffing and Analyzing GSM Signals with GR-GSM

Over a year ago we wrote a tutorial on how to analyze GSM cellular phone signals using a RTL-SDR, a Linux computer with GNU Radio, Wireshark and a GSM decoder called Airprobe. With this combination it is possible to easily decode GSM system messages. Setting up Airprobe is can be difficult as it is unmaintained and incompatible with the new version of GNU Radio without patches.

Now a new software package called gr-gsm has been released on GitHub which seems to be a newer and improved version of Airprobe. The gr-gsm software is also much easier to install, uses the newer GNU Radio 3.7 and seems to decode the system data with much less trouble than Airprobe did. We will soon update our tutorial to use gr-gsm, but the instructions on the GitHub are already quite good. The author of gr-gsm also appears to be actively adding new features to the software as well. The video below shows gr-gsm in action.

6 comments

  1. frog

    So i bought the RTL-SDR from you guys, and followed you instructions on the video. My flowchart does not look anything like that. just has two boxes. At the risk of saying you sent me a faulty unit, i’d like to resolve this issue.

    • admin

      The dongle itself has nothing to do with the software and can’t magically change the flowchart you are seeing. I’m guessing that you’re seeing the default GNU Radio flowchart, and the gr-gsm flowchart failed to load for whatever reason.

  2. josh

    I am trying to run gr-gsm with rtl-sdr or a Raspberry Pi-B, it decodes a couple of messages then it start showing overflow 00000. The same code and rtl-sdr works fine on a PC. I guess the issue is related to the 2MSps sampling rate. I tried to reduce it to 300 KHz (something above 270.03 KHz), but nothing works. Any help is much appreciated.

  3. Piotr

    rayn – can you show your test setup to measure sensitivity? I’m interested in replicating it in order to increase effectiveness of demodulation.

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