ads-b格式文档.pdf

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Table of Content

Introduction

ADS-B

ADS-B message types

ADS-B Checksum

Aircraft Identification

Airborne Positions

First, ``odd'' or ``even'' message?

CPR parameters and functions

Latitude/Longitude calculation

Altitude Calculation

The final position

Airborne Velocity

Decoding message subtype 1 or 2

Decoding message subtype 3 or 4

NIC / NAC

NIC and Rc

NAC and HFOM

Tips on ADS-B

The message structure

The CPR positions

Aircraft Identification

More than just ADS-B data

What's next?

Mode S Enhanced Surveillance (EHS)

Documents, code, and data

Contact

About us

References

ADS-B Decoding Guide Documentation Release 0.2 Junzi Sun July 08, 2016

Contents 1 Table of Content . . . . . . . . . . . 1.1 Introduction . 1.1.1 1.1.2 1.1.3 . . ADS-B . . ADS-B message types ADS-B Checksum . . . 1.2 Aircraft Identiﬁcation . . 1.3 Airborne Positions . . . . . . . . . . . 1.3.1 1.3.2 1.3.3 1.3.4 1.3.5 1.4 Airborne Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . First, “odd” or “even” message? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CPR parameters and functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Latitude/Longitude calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Altitude Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The ﬁnal position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Decoding message subtype 1 or 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Decoding message subtype 3 or 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5.2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tips on ADS-B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.2 1.6.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6.4 More than just ADS-B data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.7 What’s next? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8 Mode S Enhanced Surveillance (EHS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The message structure The CPR positions . . Aircraft Identiﬁcation . . . NIC and Rc . . NAC and HFOM . . 1.5 NIC / NAC . 1.4.1 1.4.2 1.6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Documents, code, and data 3 Contact 4 About us 5 References 3 3 3 4 4 4 5 6 6 7 9 10 10 10 12 13 14 15 15 15 15 15 16 16 16 17 19 21 23 i

ADS-B Decoding Guide Documentation, Release 0.2 This is a small research project conducted by Junzi Sun at TuDelft. While we were trying to work with ADS-B data col- lected from our receiver, we notice that there are very few documents available which can explain the ADS-B data com- prehensively. So, we created this guide, along with a decoder written in python (https://github.com/junzis/pyModeS). Have Fun! Contents 1

ADS-B Decoding Guide Documentation, Release 0.2 2 Contents

CHAPTER 1 Table of Content The main focus of the guide is on reading different types of messages, understanding the information in the message, and decoding/computing aircraft status. 1.1 Introduction 1.1.1 ADS-B ADS-B is short for Automatic Dependent Surveillance–Broadcast. it is a satellite based survillance system. Aircraft position, velocity, together with identiﬁcation are transmitted through Mode-S Extended Squitter (1090 MHz). Majority of the aircraft nowadays are broadcasting ADS-B messages constantly. There are many ways you can set up you own receiver and antenna to start tapping into those signals (DVB-T usb stick, ModeSBeast, Raspberry Pi, RadarScape, etc). An ADS-B message is 112 bits long, following is an example: BIN format: 10001101010010000100000011010110001000000010110011000011 01110001110000110010110011100000010101110110000010011000 HEX format: 8D4840D6202CC371C32CE0576098 This table lists the key bits of a message: Name Downlink Format Message Subtype ICAO aircraft address Data frame Parity check Bit from Bit to 1 6 9 33 89 Abbr. DF CA ICAO24 DATA PC 5 8 32 88 112 The type of the message can be identiﬁed by checking its Downlink Format (DF), bit 1 to 5. For ADS-B message, we need: DF = 17 (in decimal), or 10001 (in binary), Within the data frame, another import value is the Type Code. it tells what is inside of the data frame, it is located from bit 33 to 37 (5 bits) Bit from Bit to 33 37 Abbr. TC Name Type Code 3

ADS-B Decoding Guide Documentation, Release 0.2 1.1.2 ADS-B message types By looking at the DF and TC we can quickly understand what kind of information is contained in the data frame. The relations are listed as following: DF 17 17 17 17 17 17 17 17 17 17 17 17 Content Aircraft identiﬁcation Surface position Airborne position (Baro Alt) Airborne velocities TC 1 to 4 5 to 8 9 to 18 19 20 to 22 Airborne position (GNSS Height) 23 24 25 to 27 Reserved 28 29 30 31 Extended squitter AC status Target state and status (V.2) Reserved Aircraft Operation status Test message Surface system status Note that within different type of the messages, the conﬁgurations of the bits in data frame are different. In next chapter, those will be explained in detail. 1.1.3 ADS-B Checksum ADS-B uses cyclic redundancy check to validate the correctness of received message. The parity check bits are the last 6 bytes (bit 89 to 112) 1.2 Aircraft Identiﬁcation An aircraft identiﬁcation message has DF: 17, and TC: 1 to 4. For example: 8D4840D6202CC371C32CE0576098 The structure of the message is: | ICAO24 | | | |----|--------|----------------|--------| | 8D | 4840D6 | 202CC371C32CE0 | 576098 | DATA | | CA | | DF |-------|-----|--------------------------|-------|-----|--------------------------------------------------|--------------------------| | 10001 | 101 | 010010000100000011010110 | 00100 | 000 | 001011001100001101110001110000110010110011100000 | 010101110110000010011000 | | ICAO24 ADDRESS | Data | TC Note that TC is inside of the DATA frame. DF and TC can be easily calculated: DF: 10001 -> 17 TC: 0010 -> 4 Those two values conﬁrm that the message is good for decoding aircraft identiﬁcation. Next, we are decoding the data frame containing the aircraft callsign (identiﬁcation). In order to get the callsign, a look-up table is needed for mapping index numbers to letters: 4 Chapter 1. Table of Content

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