Airplane Tracking Using ADS-B Signals in Simulink

Required Hardware and Software

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

Introduction

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.

Receiver Structure

This diagram summarizes the receiver code structure. The processing has four main parts: signal source, physical layer, message parser, and data viewer.

Signal Source

You can specify one of these signal sources:

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 referred 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.

Physical Layer

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:

Message Parser

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.

Data Viewer

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).

These figures illustrate how the application tracks and lists flight details and displays them on a map.

References