Airplane Tracking Using ADS-B Signals in Simulink
This example shows how to track planes by processing automatic dependent surveillance-broadcast (ADS-B) signals using Simulink® and Communications Toolbox™. You can use captured and saved signals, or receive signals in real time using an RTL-SDR radio, an ADALM-PLUTO radio or a Universal Software Radio Peripheral (USRP™) radio. You can also visualize the tracked planes on a map, if you have the Mapping Toolbox™ software.
Required Hardware and Software
To run this example using captured signals, you need Simulink® and Communications Toolbox™ software.
To receive signals in real time, you also need one of these SDR devices and the corresponding software add-on:
An RTL-SDR radio and Communications Toolbox Support Package for RTL-SDR Radio add-on
An ADALM-PLUTO radio and Communications Toolbox Support Package for Analog Devices® ADALM-PLUTO Radio add-on
A USRP radio and the corresponding Communications Toolbox Support Package for USRP Radio Add-On
For a full list of Communications Toolbox supported SDR platforms, refer to Supported Hardware section of Software Defined Radio (SDR) discovery page.
For an introduction on the Mode-S signaling scheme and ADS-B technology for tracking aircraft, refer to the Airplane Tracking Using ADS-B Signals MATLAB® example.
This diagram summarizes the receiver code structure. The processing has four main parts: signal source, physical layer, message parser, and data viewer.
You can specify one of these signal sources:
''Captured Signal''- Over-the-air signals written to a file and sourced using a baseband file reader block at 2.4 Msps
''RTL-SDR Radio''- RTL-SDR radio at 2.4 Msps
''ADALM-PLUTO''- ADALM-PLUTO radio at a sample rate of 12 Msps
''USRP Radio''- USRP radio at a sample rate of 20 Msps for all radios except N310/N300 radio, that uses 2.4 Msps sample rate
The extended squitter message is 120 micro seconds long, so the signal source is configured to process enough samples to contain 180 extended squitter messages simultaneously, and set
SamplesPerFrame of the signal property accordingly. The rest of the algorithm searches for Mode-S packets in this frame of data and outputs all correctly identified packets. This type of processing is reffered to as batch processing. An alternative approach is to process one extended squitter message at a time. This single packet processing approach incurs 180 times more overhead than the batch processing, while it has 180 times less delay. Since the ADS-B receiver is delay tolerant, you use batch processing in this example.
The physical layer (PHY) processes baseband samples from the signal source to produce packets that contain the PHY layer header information and the raw message bits. This diagram shows the physical layer structure.
The RTL-SDR radio can use a sampling rate in the range [200e3, 2.8e6] Hz. When the source is an RTL-SDR radio, the example uses a sampling rate of 2.4 MHz and interpolates by a factor of 5 to a practical sampling rate of 12 MHz.
The ADALM-PLUTO radio can use a sampling rate in the range [520e3, 61.44e6] Hz. When the source is an ADALM-PLUTO radio, the example samples the input directly at 12 MHz.
The USRP radios are capable of using different sampling rates. When the source is a USRP radio, the example samples the input directly at 20 MHz. For the N310/N300 radio the data is received at 2.4 MHz sample rate and interpolates by a factor of 5 to a practical sampling rate of 12e6.
For example, if the data rate is 1 Mbit/s and the effective sampling rate is 12 MHz, the signal contains 12 samples per symbol. The receive processing chain uses the magnitude of the complex symbols.
The packet synchronizer works on subframes of data that is equivalent to two extended squitter packets, i.e. 1440 samples at 12 MHz or 120 micro seconds. This subframe length ensures that the subframe contains the whole extended squitter. Packet synchronizer first correlates the received signal with the 8 microsecond preamble and finds the peak value. The synchronizer then validates the found synchronization point by checking if it confirms to the preamble sequence, [1 0 0 0 0 0 1 0 1 0 0 0 0 0 0], where a value of 1 represents a high value and a value of 0 represents a low value.
The Mode-S PPM scheme defines two symbols. Each symbol has two chips, where one has a high value and the other has a low value. If the first chip is high and the subsequent chip is low, then the symbol is 1. Alternatively, if the first chip is low and subsequent chip is high, then the symbol is 0. The bit parser demodulates the received chips and creates a binary message. The CRC checker validates the binary message. The output of bit parser is a vector of Mode-S physical layer header packets that contains these fields:
RawBits - Raw message bits
CRCError - FALSE if CRC passes, TRUE if CRC fails
Time - Time of reception in seconds, from the start of reception
DF - Downlink format (packet type)
CA - Capability
The message parser extracts the raw bits based on the packet type as described in [ 2 ]. This example can parse short squitter packets and extended squitter packets that contain airborne velocity, identification, and airborne position data.
The data viewer shows the received messages on a graphical user interface (GUI). For each packet type, the data viewer shows the number of detected packets, the number of correctly decoded packets and the packet error rate (PER). As the radio captures data, the application lists information decoded from these messages in a table.
Launch Map and Log Data
You can also launch the map and start text file logging using the two slider switches(Launch Map and Log Data).
Log Data* - When Log Data is On, it Saves the captured data in a TXT file. You can use the saved data for later for post processing.
Launch Map - When Launch Map is On, map will be launched where the tracked flights can be viewed. NOTE: You must have a valid license for the Mapping Toolbox if you want to use this feature.
These figures illustrate how the application tracks and lists flight details and displays them on a map.
International Civil Aviation Organization, Annex 10, Volume 4. Surveillance and Collision Avoidance Systems.
Technical Provisions For Mode S Services and Extended Squitter (Doc 9871)