An AIS Decoder for MATLAB and the RTL-SDR

RTL-SDR.com reader Mike wrote in to us today to let us know that he has released his AIS decoder for MATLAB and the RTL-SDR. MATLAB is a technical computing language used by many scientists and engineers in the world. Mike writes the following about his work:

Automatic Identification System (AIS) is a communication standard that is used by commercial and recreational maritime vessels to report a ship’s ID, position, course and other information. This data is used for collision avoidance, search and rescue and many other applications. AIS has the following characteristics:

  • Access protocol: Self-organizing Time Division Multiple Access (SOTDMA)
  • Transmission frequencies: 161.975 MHz and 162.025 MHz
  • Transmit Power: 2 W or 12.5 W
  • Modulation: Gaussian Minimum Shift Keying (GMSK)
  • Data Rate: 9600 bits per second

An AIS decoder that uses the RTL-SDR and MATLAB to capture AIS transmissions is posted on MATLAB Central, the MathWorks file sharing exchange. The decoder has three main components

  1. Software to connect MATLAB to the RTL-SDR and bring IQ data directly into the MATLAB workspace (http://www.mathworks.com/hardware-support/rtl-sdr.html)
  2. Demodulation and decoding algorithms to convert the IQ samples into bits and decode the AIS data (http://www.mathworks.com/products/communications/)
  3. A user interface to configure the RTL-SDR, launch the capture and decoding process, and display the decoded messages (http://www.mathworks.com/matlabcentral/fileexchange/57600-ais-decoder)

The MATLAB Central post includes MATLAB source code for the AIS decoder, captured data files from Boston and San Francisco, an app for easy configuration and operation of the decoder, and instructions for installing the RTL-SDR Hardware Support Package and AIS Decoder app.

If you want to learn how AIS works, and how to write a decoder, then a MATLAB example like this is an excellent resource.

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