gr-ais

An AIS receiver for GNU Radio 3.10. Decodes GMSK transmissions into NMEA !AIVDM sentences using coherent Viterbi demodulation, NRZI decoding, and HDLC deframing with CRC checks.

Build and test

The Ubuntu 24.04 devcontainer includes the build dependencies and development tools. Open the repository in VS Code and select Dev Containers: Reopen in Container, then follow its build instructions.

For a native Ubuntu 24.04 build:

sudo apt update
sudo apt install build-essential cmake ninja-build gnuradio gnuradio-dev \
    pybind11-dev python3-dev python3-numpy python3-packaging python3-pygccxml castxml
cmake -S . -B build/local -G Ninja -DCMAKE_BUILD_TYPE=Release \
    -DCMAKE_INSTALL_PREFIX=/usr/local -DPYTHON_EXECUTABLE=/usr/bin/python3
cmake --build build/local --parallel 2
ctest --test-dir build/local --output-on-failure
sudo cmake --install build/local
sudo ldconfig

Receive

Live reception requires GNU Radio's SoapySDR support and a driver for your SDR. For example, with an RTL-SDR:

ais_rx --args="driver=rtlsdr" --rate=250e3

The receiver tunes to 162 MHz and decodes both AIS channels. Use --singlechannel to tune to channel A at 161.975 MHz. Decoded sentences are printed to stdout.

Files and UDP streams accept raw interleaved float32 I/Q samples. Match --rate to the recording or stream; use samples centered at 162 MHz for both channels, or at 161.975 MHz with --singlechannel.

ais_rx --source=capture.cf32 --rate=250e3
ais_rx --source=udp:1234 --rate=250e3
ais_rx --help

Python blocks

Import blocks with from gnuradio import ais. The CLI uses the streaming ais_demod receiver. ais_burst_demod(samples_per_symbol) provides a separate data-aided receiver for isolated bursts at an integer number of samples per symbol. Its default permits adjacent single-slot bursts; set burst_slots for captures with known longer bursts. Frame length is not detected automatically.

License: GPL-3.0-or-later.