1. Jointly Presented by Australia and Hong Kong, China
GUILDANCE MATERIAL ON GENERATION, PROCESSING & SHARING OF ASTERIX CATEGORY 21 ADS-B MESSAGES
Jointly Presented by Australia and Hong Kong, China
ADS-B SITF/11
April 2012
Civil Aviation Department Hong Kong, China

2. Introduction
“All Purpose Structured Eurocontrol Surveillance Information Exchange” (ASTERIX) Category 21
A data format standard globally accepted by the Air Traffic Management (ATM) system manufacturing industry for sharing of ADS-B data with ATM automation systems
Used to convey ADS-B data from ADS-B ground stations to ATC processing and display system
Civil Aviation Department Hong Kong, China

3. ASTERIX Cat 21 in Asia Pacific (APAC) Regions
During the 16th APANPIRG Meeting held in August 2005
ASTERIX Category 21 version 0.23 which has incorporated DO260 standard was adopted as
the baselined ADS-B data format for deployment of ADS-B ground stations
sharing of ADS-B data in the APAC Regions
DO260A and DO260B standards have yet been fully defined during that period
Civil Aviation Department Hong Kong, China

4. Evolution of ASTERIX Cat 21
Asterix standard has been developed over many years
Undergone continuous revisions to incorporate the latest ADS-B link technology
November 2003
August
2005
August 2008
May 2011
16th APANPIRG adopted Version 0.23 as baselined version for APAC
Version 2.1
(incorporated DO260B standard)
Version 1.0
(incorporated DO260A
standard)
Version 0.23
(Incorporated DO260 standard)
Civil Aviation Department Hong Kong, China

5. Choice of ASTERIX Version Number
Asia Pacific decided to use V0.23 as the version for sharing ADS-B data between States in 2005
V0.23
Provides adequate information for ATC operational services
Can be used with DO260, DO260A and DO260B ADS-B avionics/ground stations to provide ATC operational services
Cannot fully support all enhanced capabilities offered by DO260A and DO260B
Civil Aviation Department Hong Kong, China

6. Choice of ASTERIX Version Number
Most of the special DO260A and DO260B data items cannot be reconstructed from a V0.23 data stream X
(V2.1 as representation of ASTERIX CAT 21 Version after V0.23)
Nearly all V0.23 data items can be reconstructed from a received V2.1 data stream
Civil Aviation Department Hong Kong, China

7. Support of DO260A/B using ASTERIX Cat 21 V0.23
V0.23 does not directly support DO260A/B
Ground station software can generate useful V0.23 Asterix data from DO260A/B reports using some techniques (e.g. generation of NUC value based on pre-defined table on combination of SIL, NIC and NAC)
A more recent version of Cat 21 is needed if there is a particular need for the ATC system to access to NIC/NAC or SIL or other data items that exist in DO260A/B
States are encouraged to review and determine additional DO260A/B fields beneficial to warrant adoption of newer versions of Asterix Cat 21
Civil Aviation Department Hong Kong, China

8. Specification of ASTERIX Message Processing
ASTERIX Cat 21 specification:
Defines characteristics of data on the interface including items as optional and mandatory on the interface
It does NOT specify the behaviour of the transmitting ground station nor behaviour of the receiving ATM automation system
Civil Aviation Department Hong Kong, China

9. Specification of ASTERIX Message Processing
ADS-B ground station specification:
Defines the Asterix standard to be adopted for outputting data and which optional Asterix data items are required to be delivered on the Asterix interface
indicates how the ground station processes and outputs every received DO260, DO260A and DO260B data element into an Asterix data element/field
indicates which and how each Asterix data element and field presented at the output are populated
Civil Aviation Department Hong Kong, China

10. Specification of ASTERIX Message Processing
ATM automation system specification:
Defines which received Asterix data element and fields are processed and how they are processed
Defines which Asterix optional data fields are required by the ATM automation system
Civil Aviation Department Hong Kong, China

11. Specification of ASTERIX Message Processing
ANSPs that specify ADS-B ground stations and ATM automation systems to consider carefully what they need to achieve
Specification which simply require compliance with a particular ASTERIX standard will be inadequate in most circumstances
Civil Aviation Department Hong Kong, China

12. Specification of ASTERIX Message Processing
ANSPs together with suppliers should:
Specify the Asterix standard version to be used
Defines the message formats that are placed on the link between ADS-B ground station and ATM automation systems
Specify the ADS-B ground station behaviour
When data is received from the aircraft, the ground station is required to fill appropriate optional Asterix data fields
Specify the ATM automation system behaviour and syntax checks applied to the Asterix data, including any triggers for the system to discard data
Civil Aviation Department Hong Kong, China

13. Generation of ASTERIX at an ADS-B Ground Station
Group 1 (Mandatory) – an Asterix Cat 21 message should not be transmitted unless the mandatory data items defined below are all present:
Data Items
Description
V0.23
V2.1
Remarks
I021/010
Data Source Identification X
Identifies source of data. Important if validity checks are performed as an anti spoofing capability
I021/030
Time of Day
Data received with a Time of Day too far in the past should be discarded
I021/071 or I021/073
Time of applicability of Position or Time of Message reception for position
Civil Aviation Department Hong Kong, China

14. Generation of ASTERIX at an ADS-B Ground Station
Group 1 (Mandatory)
Data Items
Description
V0.23
V2.1
Remarks
I021/040
Target Report Descriptor X
Indicates if report is a duplicate, on the ground, is a simulated target, is a test target. This needs to be checked by ATC system prior to processing.
I021/080
Target Address
Included in all 1090ES downlink messages, so always available. Used for report/report linkage in ATC tracking.
I021/090
Figure of Merit/Quality Indicators
Position cannot be used without quality indicator
I021/130
Position in WGS-84 co-ordinates
Report cannot be used without position
Civil Aviation Department Hong Kong, China

15. Generation of ASTERIX at an ADS-B Ground Station
Group 2 (Operationally Desirable) - should always be transmitted whenever data are received by the ground station from aircraft (if allowed by relevant Asterix standard chosen):
Data Items
Description
V0.23
V2.1
Remarks
I021/008
Aircraft operational Status X
TCAS capability, Target state reporting capability, CDTI capability, Single/dual aircraft antenna
I021/020
Emitter Category
Aircraft or vehicle type
I021/140
Geometric Altitude/Height
Useful for RVSM monitoring
I021/145
Flight Level
Flight level is an important information to ATC
Civil Aviation Department Hong Kong, China

16. Generation of ASTERIX at an ADS-B Ground Station
Group 2 (Operationally Desirable)
Data Items
Description
V0.23
V2.1
Remarks
I021/155
Barometric Vertical Rate X
Used for predictive tools and safety nets.
I021/157
Geometric Vertical Rate
I021/160
Ground Vector
Provides excellent vector to support extrapolation of positional data to time of display
I021/170
Target Identification
This is the callsign/Flight ID is extremely useful for ATC and matching to the flight plan (if any)
I021/200
Target Status
This is the emergency type and is highly desirable
Civil Aviation Department Hong Kong, China

17. Generation of ASTERIX at an ADS-B Ground Station
Group 3 (Optional) – remaining data items belong to this Group which may need to be transmitted depending on availability of such data from aircraft and/or other specific operational needs
Specification for ADS-B ground station should take into account:
Transmission of all Group 1 (Mandatory) and Group 2 (Operationally Desirable) data items
Whether Group 3 (Optional) data items will be transmitted should be configurable on item-by-item basis depending on specific operational needs and link bandwidth availability
Civil Aviation Department Hong Kong, China

18. Processing of ASTERIX ADS-B Data at ATC System
An Asterix Cat 21 message should not be accepted by the ATC System for processing unless it includes at least all Group 1 data items
The ATC system should process all received Asterix Cat 21 message data items that bring operational benefits. The ATC System should appropriately process those Group 2 data items depending on operational need
Whether the ATC system will process Group 3 optional data items will depend on specific operational needs
Civil Aviation Department Hong Kong, China

19. Data Sharing of ASTERIX ADS-B Data
Data items that should be included in data sharing:
Group 1 (Mandatory)
Group 2 (Operationally Desirable)
when such data are received from aircraft
Subject to mutual agreement between the two data sharing parties concerned, Group 3 (Optional) data items needs to be shared
Civil Aviation Department Hong Kong, China

20. ADS-B Format Conversion and Filter System
Evolution of 1090ES ADS-B link technology and avionics standards will continue
Asterix standards will continue to evolve
ATC systems need to be adaptable and be able to cope with new functionality requirements and new message standards
Civil Aviation Department Hong Kong, China

21. ADS-B Format Conversion and Filter System
Provides ADS-B format conversion between domestic and foreign ADS-B systems
Allows data meeting agreed sharing criteria to be passed through
Cost-effective way to provide the necessary protection and flexibility to adapt to new message standards
Civil Aviation Department Hong Kong, China

22. ADS-B Format Conversion & Filter System
ADS-B Ground Station
Asterix CAT 21
Version “XA”
ATM Automation
System
Asterix CAT 21
Version “YA”
ANSP “A”
Ver “XA”
Ver “YA”
ADS-B Format Conversion & Filter System
Asterix Format Converter : Domestic: Ver XA / Ver YA ; Foreign: Ver XA / Ver YB
Pass only data that meet sharing criteria
Security features
Agreed sharing format
Ver “YB”
Ver “YA”
ADS-B Format Conversion & Filter System
Asterix Format converter : Domestic: Ver XB / Ver YB ; Foreign: Ver XB / Ver YA
Pass only data that meet sharing criteria
Security features
Ver “YB”
Ver “XB”
ATM Automation
System
Asterix CAT 21
Version “YB”
ADS-B Ground Station
Asterix CAT 21
Version “XB”
ANSP “B”
Domestic Data
Foreign Data
Civil Aviation Department Hong Kong, China

23. Conclusion
To recognize differences between DO-260, DO260A, DO260B for ADS-B ground stations and Asterix Cat 21
To agree on proposed mandatory, desirable and optional ADS-B data fields for sharing of ADS-B data in Asterix Cat 21 format to ensure system interoperability and harmonize ADS-B implementation in APAC Regions
To take note of possibility of deploying ADS-B format conversion & filter (ADS-B FC&F) system in overall design and integration of ATM automation systems and ADS-B ground stations
To adopt this “Guidance Material on Generation, Processing and Sharing of Asterix Category 21 ADS-B Messages” for use by APAC States/Administrations
Civil Aviation Department Hong Kong, China

24. Thank you
Civil Aviation Department Hong Kong, China