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TETRA


Overview

TETRA is an acronym for TErrestrial Trunked RAdio. Tetra is an open voice standard developed by the European Telecom Standards Institute (ETSI) and is in use primarally overseas and in Europe. The first users to implement TETRA are the European public safety and emergency services, i.e. police, fire brigades, EMS, border control officials, etc. The existing public safety networks are coming to the end of their economic lifetime and TETRA provides the key features like equiment standardisation, direct mode, encryption and last call set-up time for these services.

TETRA uses a 4-slot TDMA channel. Tetra systems uses both Voice and Control Channel. It can use strong encryption on the air interface, and this is usually used on sensitive traffic (police etc), but commercial networks are often unencrypted. There is currently no scanner available that can monitor TETRA Voice, however software to do it exists (telive, w-code, and probably others).

TETRA Modulation Characteristics
Property Value
Modulation π/4 DQPSK
Symbol rate 18000
Bit rate 36000
Slots/frame 4
Frame length 255 symbols (56.7ms)
Frame rate 17.65Hz

TETRA decoders

  • osmo-tetra - is a open source tetra decoder using linux, gnuradio and USRP1/2 for signal processing. The osmo-tetra project aims at implementing the sending and receiving part of the TETRA MAC/PHY layer. You can learn more about how TETRA works on its lowest level, but no decryption. Currently, it can receive, demodulate TETRA downlink signals of real-world TETRA networks display information about SYNC, SYSINFO, MM and CMCE PDUs.
  • telive - telive is a frontend for patched osmo-tetra and friends: osmo-tetra-sq5bpf, libosmocore-sq5bpf. Telive will display a console showing current SSI numbers, and have the option to log signalling information, decode some SDS messages, record traffic (and recompress it into OGG files), and do live listening. The program will decode some location protocols, and provide the decoded data in a KML file (readable by Google Earth and other software). The receiver uses an rtl-sdr dongle and gnuradio (3.6, or 3.7.5 or higher), but the software was also reported working with a funcube dongle and USRP. The software can process multiple channels at once, and gnuradio-companion receiver flowgraphs are provided to monitor multiple channels with one sdr dongle. Please read the documentation and the Tetra decoding Thread
on Radioreference. All software runs on linux and is fully opensource (except for the ACELP codec from ETSI).
  • w-code - W-CODE is commercial software from Wavecom, which can analyze and decode many modes, including tetra.

Links




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