Ship Tracking Using AIS Signals

Required Hardware and Software

By default, this example runs using previously captured signals. Optionally, you can receive signals over-the-air. For this, you also need one of the following:

Overview

In marine transportation, vessel traffic services use AIS as a component of the marine traffic monitoring system. AIS performs these functions:

AIS has these attributes:

AIS transmission packets contain these fields:

This figure shows the AIS packet format

Receiver Structure

This block diagram shows the receiver code structure. The processing has three main parts: signal source, physical layer and data viewer.

Signal Source

Specify the signal source as one of these values

The example uses a signal symbol rate of 9600 Hz and 24 samples per symbol.

If you specify ''RTL-SDR'' as the signal source, the example searches your computer for an RTL-SDR radio at the radio address '0' and uses that radio as the signal source.

If you specify ''ADALM-PLUTO'' as the signal source, the example searches your computer for a Pluto radio at the radio address 'usb:0' and uses that radio as the signal source.

If you specify ''USRP'' as the signal source, the example searches your computer for a USRP radio at the radio address you specify and uses that radio as the signal source.

Physical Layer

The physical layer (PHY) processes the baseband samples from the signal source to produce packets that contain the ship position information and raw message bytes. This figure shows the PHY processing components.

AIS signal contains 64 specific message types. Ship position information is included in 11 of the message types. In this example, you decode all of the 11 message types that contain ship position information.

This example lists the ship position information including the ship ID, latitude, and longitude, as well as the associated date and time in a table. For decoding additional information from the messages, see [1].

Data Viewer

The data viewer shows the received messages on a graphical user interface (GUI). As data is captured, the application lists information that it decodes from these messages in a table.

Track Ships Using AIS Signals

The default configuration runs for a duration of 10 seconds and uses signal data from a captured data file, and outputs to a text file. To provide input values from the command line, you must change cmdlineInput to 1, then you will be prompted to enter the following information when you run the example:

cmdlineInput = 0;
if cmdlineInput
    % Request user input from the command-line for application parameters
    userInput = helperAISUserInput;
else
    load('defaultInputs.mat');
end
% Calculate AIS parameters based on the user input
[aisParam,sigSrc] = helperAISConfig(userInput);

% Create the data viewer object and configure based on user input
viewer = helperAISViewer('LogFileName',userInput.LogFilename, ...
                         'SignalSourceType',userInput.SignalSourceType);

% Launch map based on user input
if userInput.LaunchMap
    startMapUpdate(viewer);
end

% Log data based on user input
if userInput.LogData
    startDataLog(viewer);
end

% Start the viewer and initialize radio time
start(viewer)
radioTime = 0;

% Main loop for capturing and decoding the AIS samples
while radioTime < userInput.Duration  
    if aisParam.isSourceRadio       
        if aisParam.isSourceRTLSDRRadio         % For RTL-SDR
            [rcv,~,lost,~] = sigSrc();
            lostFlag = logical(lost);         
        elseif aisParam.isSourcePlutoSDRRadio   % For ADALM-PLUTO
            [rcv,~,lostFlag] = sigSrc();
        elseif aisParam.isSourceUSRPRadio       % For USRP
            [rcv,~,lostFlag] = sigSrc(); 
        end
    else                                        % For baseband file
        rcv = sigSrc();
        lostFlag = uint32(0);
    end

    % Recover the information by decoding AIS samples
    [info, pkt] = helperAISRxPhy(rcv,aisParam);

    % View decoded information on viewer
    update(viewer, info, pkt, lostFlag);

    % Update radio time
    radioTime = radioTime + aisParam.FrameDuration;
end

% Stop the viewer and release the signal source
stop(viewer)

release(sigSrc)

If you have the Mapping Toolbox, you can also observe AIS tracking of ships on a map.

Further Exploration

You can investigate AIS signals using the AISExampleApp. To launch the app, enter AISExampleApp in the MATLAB® Command Window. Use the app interface to select the signal source and change the duration.

You can explore the supporting functions and System objects for details of the physical layer implementation.

References

[1] Recommendation ITU-R M.1371-5. "Technical characteristics for an automatic identification system using time division multiple access in the VHF maritime mobile frequency band", International Telecommunication Union. https://www.itu.int/rec/R-REC-M.1371-5-201402-I/en