Required Hardware and Software

To run this example using captured signals, you need the following software:

To receive signals in real time, you also need one of the following SDR devices and the corresponding support package Add-On:

For a full list of Communications Toolbox supported SDR platforms, refer to Supported Hardware section ofSoftware Defined Radio (SDR) discovery page.

Introduction

For an introduction on the Mode-S signaling scheme and ADS-B technology for tracking aircraft, refer to theAirplane Tracking Using ADS-B SignalsMATLAB® example.

Receiver Structure

The following block diagram summarizes the receiver code structure. The processing has four main parts: Signal Source, Physical Layer, Message Parser, and Data Viewer.

Signal Source

This example can use signal sources from a:

Here 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 at once, and setSamplesPerFrame信号的相应属性。其余的e algorithm searches for Mode-S packets in this frame of data and outputs all correctly identified packets. This type of processing is defined 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, batch processing was used.

Physical Layer

The baseband samples received from the signal source are processed by the physical (PHY) layer to produce packets that contain the PHY layer header information and the raw message bits. The following diagram shows the physical layer structure.

The RTL-SDR radio is capable of using a sampling rate in the range [200e3, 2.8e6] Hz. When RTL-SDR radio is the source, the example uses a sampling rate of 2.4e6 Hz and interpolates by a factor of 5 to a practical sampling rate of 12e6 Hz.

The ADALM-PLUTO radio is capable of using a sampling rate in the range [520e3, 61.44e6] Hz. When the ADALM-PLUTO radio is the source, the example samples the input directly at 12 MHz.

With the data rate of 1 Mbit/s and a practical sampling rate of 12 MHz, there are 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 a whole extended squitter packet can be found in the subframe. Packet synchronizer first correlates the received signal with the 8 microsecond preamble and finds the peak value. Then, it 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 '1' represents a high value and a '0' represents a low value.

The Mode-S PPM modulation 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 followed by low chip, this corresponds to the symbol being a 1. Alternatively, if the first chip is low followed by high chip, then the symbol is 0. The bit parser demodulates the received chips and creates a binary message. The binary message is validated using a CRC checker. The output of bit parser is a vector of Mode-S physical layer header packets that contains the following fields:

Message Parser

The message parser processes 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 number of detected packets, the number of correctly decoded packets and the packet error rate (PER) is shown. As data is captured, the application lists information decoded from these messages in a tabular form.

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).

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

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