Department of Science and Technology
Institutionen för teknik och naturvetenskap
Linköpings Universitet
Linköpings Universitet
Examensarbete
LITH-ITN-KTS-EX--02/34--SE
Technical Verification and
Validation of ADS-B/VDL Mode 4
for A-SMGCS
Matts Eriksson & Jonas Lundmark
LITH-ITN-KTS-EX--02/34--SE
Technical Verification and
Validation of ADS-B/VDL Mode 4
for A-SMGCS
Examensarbete utfört i Kommunikations- och
transportsystem vid Linköpings Tekniska Högskola,
Campus Norrköping
Matts Eriksson & Jonas Lundmark
Handledare: Christian Axelsson och Tobias Andersson
Examinator: Peter Värbrand
Rapporttyp Report category Licentiatavhandling X Examensarbete C-uppsats X D-uppsats Övrig rapport _ ________________ Språk Language Svenska/Swedish X Engelska/English _ ________________ Titel Title
Technical Verification and Validation of ADS-B/VDL Mode 4 for A-SMGCS
Författare
Matts Eriksson & Jonas Lundmark
Sammanfattning
Abstract
This report is a technical verification and validation of ADS-B (Automatic Dependent Surveillance – Broadcast) over VDL Mode 4 (Very High Frequency Data Link Mode 4) for the use in the surveillance element of an A-SMGCS (Advanced Surface Movement Guidance and Control System).
The main objective of this report is to examine if ADS-B/VDL Mode 4 fulfils the technical requirements for an implementation at Arlanda airport, Stockholm Sweden. The report also includes a FMECA (Failure Mode, Effects and Criticality Analysis), a theoretical background and methods for monitoring.
The process of making this report can be divided into three phases:
1. Preliminary Study. In this phase the requirements were examined and structured.
2. Verification. In this phase the system performance has been verified both theoretically and by several tests at Arlanda Airport. Simulation results have also been used.
3. Validation and documentation. The tests and verifications that were performed in phase 2 were validated in the third phase of the project. The final project document was also written in this phase.
The main conclusion from this analysis is that ADS-B/VDL Mode 4 is well suited for surveillance. ADS-B/VDL Mode 4 has the possibility to fulfil all considered requirements, apart from detecting all obstacles. But if all the requirements are going to be fulfilled depends both on the implementation and the operational environment.
The results from this verification and validation should be used as the technical subset in a future safety case, both in Sweden and internationally.
ISBN
_____________________________________________________ ISRN LITH-ITN-KTS-EX--02/34--SE
_________________________________________________________________
Serietitel och serienummer ISSN
Title of series, numbering ___________________________________
Nyckelord
Keyword
Datum
Date 2002-12-16
URL för elektronisk version
Avdelning, Institution
Division, Department
Institutionen för teknik och naturvetenskap Department of Science and Technology
Acknowledgements
We would like to thank all the people at SCAA ASD/MAC and our contacts at Linköpings universitet, Campus Norrköping for their support and assistance in developing this thesis.
Special thanks to:
• Tobias Andersson, supervisor at Linköpings universitet • Christian Axelsson, supervisor at SCAA ASD/MAC
• Niclas Gustavsson, SCAA ASD/MAC, giving us the opportunity to perform our Master Thesis at the SCAA
Programme/Area: TEN-T/DG TREN Project Number: 2001/EU/SE/GR-5003
Project Title: North European ADS-B Network Update Programme, Phase II (NUP II)
Document Id: SCAA_NUP_WP33_TVV_ADS-B_A-SMGCS_1.0 Internal Reference: NA Version: 1.0 Work package: 33 Date: Date: 2002-12-16 Status: Released Classification: Public
Author(s): Matts Eriksson and Jonas Lundmark/SCAA (matts.eriksson@lfv.se) (jonas.x.lundmark@lfv.se)
Technical Verification and Validation of
ADS-B/VDL Mode 4 for A-SMGCS
Document Identification
Programme: TEN-T/DG TREN Project Number 2001/EU/SE/GR-5003
Project Title: North European ADS-B Network Update Programme, Phase II Project Acronym NUP II
Chairman of Steering Committee Mr. Bo Redeborn, SCAA +46 1119 2388
bo.redeborn@lfv.se
Project Technical Manager Mr. Niclas Gustavsson, SCAA +46 1119 2273
niclas.gustavsson@lfv.se
Partners Swedish Civil Aviation Administration, SCAA NAVIAIR
Finnish Civil Aviation Administration, FCAA TERN
Norwegian Air Traffic and Airport Management, NATAM Scandinavian Airline Systems, SAS
Lufthansa, Deutsche Lufthansa, DLH Deutsche Flugsicherung GmbH, DFS DGAC/STNA
Airbus France Austro Control ADS-B Scatsta
EUROCONTROL Experimental Centre, EEC Belgocontrol
AVTECH Sweden AB
Document title Technical Verification and Validation of ADS-B/VDL Mode 4 for A-SMGCS
Document Id SCAA_NUP_WP33_TVV_ADS-B_A-SMGCS_1.0 Organisation Internal Reference NA
Work Package No 33 Version 1.0
Status Released Classification Public
Date Date: 2002-12-16
Author(s) Matts Eriksson and Jonas Lundmark/SCAA (matts.eriksson@lfv.se) (jonas.x.lundmark@lfv.se) Organisation maintaining document SCAA
File SCAA_NUP_WP33_TVV_ADS-B_A-SMGCS_0.1 Printed 2003-01-08
Abstract
This report aims to be a technical verification and validation of ADS-B/VDL Mode 4 for the use in an A-SMGCS at Arlanda Airport, Sweden. The purpose of the document is to make a foundation for future implementations of ADS-B
Distribution List
Name Organisation
ANDERSSON, Tobias Linköping University AXELSSON, Christian SCAA
BEVONIUS, Jörgen SCAA
CHAUDRY, Kashif Linköping University COLLIN, Bengt Eurocontrol
DANIELSSON, Lars SCAA ERIKSSON, Matts SCAA GUSTAVSSON, Niclas SCAA GRANBERG, Petter SCAA
HÖGBERG, Per ATA SCAA
KARADZA, Elma Linköping University VAN DER KRAAN, Pieter Eurocontrol
LI, Roger SCAA
LUNDMARK, Jonas SCAA
MALÈN, Harald SCAA
Control Page
This version supersedes all previous versions of this document.
Version Date Author(s) Pages Reason
0.0 2002-06-27 M.E, J.L/SCAA All New document 0.1 2002-10-02 M.E, J.L/SCAA All In Preparation 0.2 2002-11-13 M.E, J.L/SCAA All In Preparation 1.0 2002-12-16 M.E, J.L/SCAA Several Last review
Table of Contents
1. Introduction...12 1.1. Method...12 1.2. Audience...12 2. Fundamentals of report ...13 2.1. Objective...13 2.2. Scope ...13 2.3. Revision...13 2.4. Structure ...13 3. Explanation of terms ...144. Introduction to VHF Data Link Mode 4 ...16
4.1. The VDL Mode 4 vision ...16
4.2. Technical description...16
4.3. Frame and slot structure ...16
4.4. VDL Mode 4 Services...17
5. Introduction to the VDL Mode 4/ADS-B technical equipment...20
5.1. Ground station ...20
5.2. Transceiver...21
5.3. Ground Network ...22
6. Introduction to A-SMGCS ...24
6.1. A-SMGCS System Description...24
7. Requirements on A-SMGCS that VDL Mode 4/ADS-B should fulfil...26
7.1. Availability...27 7.2. Integrity...29 7.3. Continuity...30 7.4. Coverage ...30 7.5. Capacity...32 7.6. Velocity ...33 7.7. Direction of movement ...33 7.8. Reference point ...33
7.9. The Reported Position Accuracy...34
7.10. Update ...38
7.11. Latency ...38
7.12. Surveillance Detection...39
8. Failure Mode, Effects and Criticality Analysis (FMECA) ...40
8.1. Scope of FMECA...40
8.2. Contents of FMECA...40
8.3. FMECA for ADS-B/VDL Mode 4...42
9. Monitoring ...47
9.1. No input from mobile transceiver GNSS-antenna ...47
9.2. No GNSS-data to mobile transceiver ...47
9.3. Not correct GNSS-data to mobile transceiver ...47
9.4. No input from mobile transceiver VHF-antenna ...47
9.5. No output from mobile transceiver VHF-antenna...47
9.6. Loss of information on data link from transceiver to ground station...48
9.7. Loss of information on data link from ground station to transceiver...48
9.8. Distortion of data on the data link from transceiver to ground station...48
9.9. Distortion of data on the data link from ground station to transceiver...48
9.10. Loss of mobile transceiver power for less than 10 seconds ...48
9.11. Loss of mobile transceiver power for more than 10 seconds...48
9.13. Loss of Ground station external power for more than 4 hours...48
9.14. Loss of GRAS to mobile transceiver ...48
9.15. Not correct GRAS to mobile transceiver ...48
10. Conclusion ...50
11. Recommendations for further work ...51
11.1. Recommendations regarding availability ...51
11.2. Recommendations regarding integrity ...51
11.3. Recommendations regarding continuity...51
11.4. Recommendations regarding update ...51
11.5. Recommendations regarding latency...52
Appendix A – Test procedures ……….….54
Appendix B – Calculation methods ………..65
List of Figures
Figure 2-1 Scope of document inside blue circle... 13
Figure 4-1 VDL Mode 4 Frame structure (ref [6], chapter 5) ... 17
Figure 4-2 Traffic Information Service – Broadcast (TIS-B) (ref [6], chapter 3) ... 18
Figure 4-3 GRAS service level 1, 2, 3 and 4 ref [9]. ... 19
Figure 5-1 The Ground station at Arlanda airport... 20
Figure 5-2 Interior and location of the ground station at Arlanda airport... 21
Figure 5-3 VDL Mode 4 Transceiver ... 21
Figure 5-4 Ground Network... 23
Figure 7-1 Simplified logging... 26
Figure 7-2 Schematic logging... 27
Figure 7-3 Location of transceivers ... 28
Figure 7-4 Coverage test; the red line shows the route driven with the test vehicle... 31
Figure 7-5 Locations of the transceivers. ... 35
Figure 7-6 Histogram horizontal radius error... 36
Figure 7-7 Reported positions plot ... 37
Figure 8-1 Scope of FMECA ... 40
Figure 11-1 Update rate ... 52
List of Tables
Table 4-1 GRAS service level 1, 2, 3 and 4 ... 19
Table 5-1 VDL Mode 4 Transceiver... 22
Table 6-1 A-SMGCS Four Level Configuration ... 25
Table 7-1 Availability ... 29
Table 7-2 Continuity ... 30
Table 7-3 Horizontal radius error... 35
Abbreviations
ADS-B Automatic Dependent Surveillance – Broadcast
A-SMGCS Advanced Surface Movement Guidance and Control System ATC Air Traffic Control
ATIS Automatic Terminal Information Service ATM Air Traffic Management
CAPS Central Access Point Server
CNS Communication, Navigation and Surveillance CRC Cyclic Redundancy Check DGNSS Differential Global Navigation Satellite System DME Distance Measuring Equipment EUROCAE European Organisation for Civil Aviation Electronics FEC Forward Error Correction
FIS-B Flight Information Service - Broadcast FMECA Failure Mode, Effects and Criticality Analysis GFSK Gassuian Frequency Shifting Key
GNSS Global Navigation Satellite System GPS Global Positioning System
GRAS Ground-based Regional Augmentation System ICAO International Civil Aviation Organisation IEC International Electrotechnical Commission LAPS Local Access Point Server
LFV Luftfartsverket (SCAA)
MAC Managing ATM system Changes MAEVA Master ATM European Validation Plan MTBCF Mean Time Between Critical Failures MTBO Mean Time Between Outages N/A Not Applicable NEAN North European ADS-B Network NOTAM NOtice To Air Men
NUCP Position Navigation Uncertainty Categories NUP NEAN Update Programme
RAPS Regional Access Point Server
RPA Reported Position Accuracy RTK Real Time Kinematic
SCAA Swedish Civil Aviation Administration (LFV) SIS Signal In Space
SMGCS Surface Movement and Guidance Control System STDMA Self-organising Time Division Multiple Access TDMA Time Division Multiple Access
TIS-B Traffic Information Service - Broadcast UTC Universal Time Co-ordinated
VDL VHF Digital Link
References
Reports:
[1] "European Manual on A-SMGCS" Final Draft (version 10),
ICAO, 2001.
[2] “Validation Framework for the NUP Phase II” (Draft 0.4),
Blandine Lemaire, Eric Hoffman, Doc. Id: EEC_NUP_WP25_02-0.4, 2002.
[3] “Minimum Aviation System Performance Specification for Advanced Surface Movement Guidance and Control System”,
Doc. Id: ED-87A, EUROCAE, 2001. [4] “SMGCS”,
Doc. id: SMR0024, SCAA, 1999.
[5] “Manual of Air Traffic Services Data Link” First edition,
Doc. Id: 9694-AN/955, ICAO, 1999.
[6] “VDL Mode 4 in CNS/ATM, Master Document” Issue II,
SCAA, 2002.
[7] “Co-ordination of CNS Ground Station transmissions over VDL Mode 4”,
Fredrik Lindblom, Doc. Id: LiTH-ITN-KTS-14-SE, 2001.
[9] “Ground-based Regional Augmentation System (GRAS) based on VDL Mode 4”
Ottmar Raeymaeckers, Gunnar Frisk, Abdul Tahir, SCAA, 2000.
[11] ”Analysis techniques for system reliability – Procedure for failure mode and effects analysis (FMEA)”
Doc. Id: IEC 812, CEI (Commisson Electrotechnique Internationale), 1985.
[12] “Failure Modes, Effects and Criticality Analysis (FMECA) for VDL Mode 4” (Draft),
Tommy Bergström, Doc. Id: CNS-DD-484, CNS System, 2001. [13] “NUP Phase II Infrastructure Plan” (version 0.7),
Harald Malén, Doc. Id: SCAA_NUP_WP20_Infrastructure Plan_02_0.7, SCAA, 2002. [14] “ADS-B in VDL Mode 4” (version 0.5),
Christian Axelsson, Doc. Id: SCAA_NUP_WP33_ADS-B in VDL Mode 4, SCAA, 2002. [15] “Preliminary Safety Assessment report” Issue 2.1,
Doc. Id: NUP-1-2K-FR-PSA-SN-001, Airsys Navigation System s GmbH, 2001. [17] “Automatic Dependent Surveillance” Edition 1.3 (Working Draft)
Doc. Id: ADS/SPE/CR-TF-REQ/D1-08, Eurocontrol
Books:
[8] “Mobil radiokommunikation”,
Lars Ahlin, Christer Frank, Jens Zander, Studentlitteratur, Lund, ISBN 91-44-01916-5, 2001. [10] “Driftsäkerhet och underhåll”
Karl-Edward Johansson, Studentlitteratur, ISBN 91-44-39111-0, 1997.
Internet:
[16] ”The Math Forum @ Drexel” http://mathforum.org/dr.math/
Executive Summary
This report is a technical verification and validation of ADS-B (Automatic Dependent Surveillance – Broadcast) over VDL Mode 4 (Very High Frequency Data Link Mode 4) for the use in the surveillance element of an A-SMGCS (Advanced Surface Movement Guidance and Control System).
The main objective of this report is to examine if ADS-B/VDL Mode 4 fulfils the technical requirements for an implementation at Arlanda airport, Stockholm Sweden. The report also includes a FMECA (Failure Mode, Effects and Criticality Analysis), a theoretical background and methods for monitoring.
The process of making this report can be divided into three phases:
1. Preliminary Study. In this phase the requirements were examined and structured.
2. Verification. In this phase the system performance has been verified both theoretically and by several tests at Arlanda Airport. Simulation results have also been used.
3. Validation and documentation. The tests and verifications that were performed in phase 2 were validated in the third phase of the project. The final project document was also written in this phase. The main conclusion from this analysis is that ADS-B/VDL Mode 4 is well suited for surveillance. ADS-B/VDL Mode 4 has the possibility to fulfil all considered requirements, apart from detecting all obstacles. But if all the requirements are going to be fulfilled depends both on the implementation and the operational environment.
The results from this verification and validation should be used as the technical subset in a future safety case, both in Sweden and internationally.
1. Introduction
This report aims to be a technical verification and validation of the VDL Mode 4 (VHF Digital Link mode 4) as data link for ADS-B-messages (Automatic Dependent Surveillance Broadcast) (described in chapter 4) for the use in the ground segment on Arlanda airport (located nearby Stockholm, Sweden). The ADS-B messages contain information about an Aircraft/vehicles position, speed, heading etc that can be displayed for pilots and air traffic controllers to provide better situation awareness. This report is also meant to be a foundation for future ADS-B implementations in Sweden and internationally.
The work has been done in the NEAN Update Program II (NUP II) project at the department Managing ATM (Air Traffic Management) system Changes (MAC) at the Swedish Civil Aviation Administration (SCAA). NUP II is sponsored by the European Commission and includes a vast number of partners from ten European states.
The main objective of the NUP II program is to establish a European ADS-B network based on global standards supporting certified applications and equipment in synergy with the European ATM concepts providing benefits to ATM stakeholders.
1.1. Method
The main method for this verification and validation has been to compare VDL Mode 4/ADS-B with the surveillance element in an A-SMGCS (Advanced Surface Movement Guidance and Control System) (described in chapter 6). The performance of the system has been verified partly theoretically and partly with a number of tests at Arlanda airport.
The project has been executed in the phases, Preliminary study, Verification and finally Validation and
documentation. The validation framework established for validation activities within NUP II, ref [2], based on
the MAEVA (Master ATM European Validation Plan) project work, has been used throughout the project. • Phase 1: Preliminary Study
In order to find the different requirements on VDL Mode 4/ADS-B that should be fulfilled, documents from the International Civil Aviation Organization (ICAO), Eurocontrol, the European Organisation for Civil Aviation Equipment (EUROCAE) and the SCAA has been scrutinized. People at the SCAA with special knowledge in different areas in an A-SMGCS have also been consulted.
• Phase 2: Verification
The test and verification phase is where the tests to verify the performance, of the VDL Mode 4/ADS-B system as the surveillance element of an A-SMGCS, at Arlanda airport have been executed. Theoretical studies have also been performed in this phase.
• Phase 3: Validation and documentation
The results from the tests and verifications that were performed in phase 2 have been validated in the third phase of the project. The final project document was also written in this phase.
1.2. Audience
The audience for this document is primarily partners in NUP II, the Swedish Aviation Safety Authority and Linköpings Universitet.
2. Fundamentals of report
2.1. Objective
The objective of this work is to find out if VDL Mode 4/ADS-B fulfils the technical requirements for the implementation of an A-SMGCS surveillance element at Arlanda Airport. The document focuses on the technical performance requirements but it also takes into consideration the operational requirements that demand certain technical functions. For example does the operational requirement Reference Point (A
common reference Point on aircraft and on vehicles should be used) demand certain technical functions.
2.2. Scope
Issues addressed in this report are the performance of ADS-B/VDL mode 4 from aircraft to ground station and vehicles to ground station, and vice versa. Performance is measured in terms of availability, continuity, integrity, latency and accuracy. Issues related to other parts of the surveillance system, for example data transfer from ground station to Air Traffic Control (ATC) or display of surveillance data at ATC have not been addressed.
Figure 2-1 Scope of document inside blue circle
2.3. Revision
It is the responsibility of the SCAA to maintain and update this document.
2.4. Structure
The report consists of:
• Introductory part (chapter 1-3)
• One part describing used terms, VDL Mode 4 and A-SMGCS (chapter 4-6)
• The main part where all requirements on VDL Mode 4/ADS-B are presented, verified and validated (chapter 7)
• One part that considers Failure Modes and Monitoring (chapter 8,9) • Conclusions & Recommendations (chapter 10,11)
3. Explanation of terms
Aerodrome A defined area on land or water (including any buildings, installations, and equipment) intended to be used either wholly or in part for arrival, departure and surface movement of aircraft. Ref [2].
Alert Situation Any situation relating to aerodrome operations that has been defined as requiring particular attention or action. Ref [3], chapter 1.3.
Apron A defined area on a land aerodrome, intended to accommodate aircraft for purposes of loading or unloading passengers, mail or cargo, fuelling, parking or maintenance. Ref [2].
Control Application of measures to prevent collisions, runway incursions and to ensure safe, expeditious and efficient movement. Ref [1], Explanation of Terms.
Coverage Volume The Coverage Volume of an A-SMGCS is defined as that volume in space which encompasses all parts of the aerodrome surface where aircraft movements take place, together with those parts of the surrounding airspace which affect surface operations.
CRC Cyclic Redundancy Check is a technique to obtain data reliability. The transmitter appends an extra n- bit sequence to every frame called Frame Check Sequence (FCS). The FCS holds redundant information about the frame that helps the transmitter detect errors in the frame.
FEC Forward Error-Correction is a type of digital signal processing that improves data reliability by introducing a known structure into a data sequence prior to transmission or storage. This structure enables a receiving system to detect and possibly correct errors caused by corruption from the channel and the receiver. As the name implies, this coding technique enables the decoder to correct errors without requesting retransmission of the original information
Guidance Facilities, information and advice necessary to provide continuous, unambiguous and reliable information to pilots of aircraft and drivers of vehicles to keep their aircraft or vehicles on the surfaces and assigned routes intended for their use. Ref [1], Explanation of Terms.
Manoeuvring area That part of an aerodrome to be used for the take-off, landing and taxiing of aircraft, excluding aprons. Ref [2].
Monitoring/Alerting A function of the system that provides dynamic interpretation of the traffic situation, including the verification of planned events, as well as the detection and alerting of conflicts and other hazards. Ref [3], chapter 1.3.
aircraft, consisting of the manoeuvring area and apron(s). Ref [2].
Routing The planning and assignment of a route to individual aircraft and vehicles to provide safe, expeditious and efficient movement from its current position to its intended position. Ref [1], Explanation of Terms.
RTK Real Time Kinematics is a process where GPS signal corrections are transmitted in real time from a reference receiver at a known location to one or more remote rover receivers. The use of an RTK capable GPS system can compensate for atmospheric delay, orbital errors and other variables in GPS geometry, increasing positioning accuracy up to within a centimeter.
Surveillance A function of the system that provides identification and accurate positional information on aircraft, vehicles and obstacles within the required area. Ref [1], Explanation of Terms.
4. Introduction to VHF Data Link Mode 4
This chapter describes the data link VDL Mode 4 and the applications Automatic Dependent Surveillance – Broadcast (ADS-B), Traffic Information Service – Broadcast (TIS-B), Flight Information Service – Broadcast (FIS-B) and Ground-based Regional Augmentation System (GRAS). VDL Mode 4 also gives the opportunity to provide a vast number of applications that are not described in this document.
This chapter is based on ref [6], [7], [8], [9].
4.1. The VDL Mode 4 vision
The VDL Mode 4 vision is expressed in ref [6], chapter 4:
“Based on the Self-organising Time Division Multiple Access (STDMA) technology, VDL Mode 4 was developed to meet the requirements for a high capacity data link supporting demanding ATM applications. The capabilities of VDL Mode 4 aim to meet the following requirements:
• To operate from gate-to-gate, on the ground and in all types of airspace, with global implementation.
• To operate without the need for complex ground infrastructure, although additional benefits may be gained if this is available.
• To offer a solution for all user groups with appropriate cost-effectiveness and performance to meet different user requirements.
• To support a range of ATM applications across all CNS domains.
In line with this vision, VDL Mode 4 is an “open-ended” system, which can be adapted to new applications as requirements become available. The VDL Mode 4 concept can thus be described as a “toolkit”.”
4.2. Technical description
VDL Mode 4 is a time-critical Very High Frequency (VHF) data link. The data link provides communications between mobile stations and between mobile stations and fixed ground stations. Mobile stations are for example aircraft and airport surface vehicles. VDL Mode 4 was developed to provide efficient exchange of short repetitive messages. The data link transmits on a 25 kHz VHF channel, from 108.000 to 136.975 MHz. A unique feature of VDL Mode 4 is the use of Self-organising Time Division Multiple Access (STDMA), invented by Håkan Lans. Time Division Multiple Access (TDMA) divides the VHF channel into frames, which furthermore is subdivided into a vast number of time slots. TDMA gives the opportunity for every station to use the whole bandwidth for the, with respect to time, non-overlapping signals. A challenge with this method is to take care of the time synchronisation. In VDL Mode 4 the time slots are synchronised to Co-ordinated Universal Time (UTC) and every slot is an opportunity for a station to transmit. The term Self-organising describes that VDL Mode 4 uses a protocol, VDL Mode 4 Interface Protocol (VIP), that does not require a ground infrastructure because of the synchronisation to UTC.
4.3. Frame and slot structure
The frame (also called superframe in VDL Mode 4) has a duration of 60 seconds and consists of 4500 slots of equal length (see Figure 4-1). This gives 75 slots per second with a duration of 13.33 ms per slot.
Current superframe Current slot Slot 1 Slot 4500 Current superframe + 1 Slot 4501 Slot 9000 1 minute 13.33ms
Figure 4-1 VDL Mode 4 Frame structure (ref [6], chapter 5)
The Global Navigation Satellite System (GNSS) primary timing source is used as a reference to maintain synchronisation between mobiles and ground stations. Ground stations also co-ordinate their transmissions with other ground stations.
4.4. VDL Mode 4 Services
The data link VDL Mode 4 gives the opportunity to implement a number of different services. The core service in the VDL Mode 4 concept is ADS-B. Also described in this document are the three services TIS-B, FIS-B and GRAS.
4.4.1. Automatic Dependent Surveillance – Broadcast
ADS-B is as mentioned above, the core service in the VDL Mode 4 concept. It is also the enabler of other services (e.g. TIS-B, FIS-B and GRAS). The ADS-B function regularly broadcasts an aircraft or vehicles identity, position, altitude, time and state vector1. This gives the opportunity for an ADS-B equipped aircraft to display all other ADS-B equipped aircraft within its coverage volume.
“ADS-B is automatic because no external stimulus is required to elicit a transmission; it is dependent because it relies on on-board navigation sources and on-board broadcast transmission systems to provide surveillance information to other users. The aircraft or vehicle originating the broadcast may or may not have knowledge of which users are receiving the broadcast; any user, either aircraft or ground-based, within the range of this broadcast, may choose to receive and process ADS-B surveillance information.” Ref [6],
chapter 3.5.5.
4.4.2. Traffic Information Service - Broadcast
The fundamental service of TIS-B is to broadcast traffic information for aircraft that are not visible via ADS-B broadcasts. If not all aircraft in the vicinity are equipped with ADS-B, TIS-B can be used to uplink radar surveillance data from ground to aircraft (Figure 4-2). This will provide airborne situation awareness of aircraft that are not ADS-B equipped to aircraft that are equipped with ADS-B and a cockpit display. Accordingly ADS-B equipped aircraft can display all aircraft (both ADS-B equipped and not ADS-B equipped) in the vicinity on the cockpit display. TIS-B would not be needed in a fully equipped ADS-B environment, but is a very important service during an implementation of an ADS-B system.
TIS-B Ground Station Radar Ground Station Processing systems Radar surveillance data Broadcast of TIS-B surveillance information ADS-B Ground Station ADS-B data
Figure 4-2 Traffic Information Service – Broadcast (TIS-B) (ref [6], chapter 3)
4.4.3. Flight Information Service - Broadcast
Flight Information Service (FIS-B) is a service to support the pilot in various phases of the flight. Examples of messages that can be included are ATIS (Automatic Terminal Information Service), NOTAM (Notice To Airmen) and meteorological data. ATIS is a voice broadcast intended to relieve frequency congestions and air traffic controller workload by providing pertinent information to aircraft operations in the terminal area through a local broadcast. The information broadcast usually last less than one minute and includes weather conditions, operating procedures etc. NOTAM is a service that provides information about changes in the airport infrastructure and airspace. This information can be sent as text messages and stored for the pilot to read when needed instead of being sent by radio at a specific radio channel as it is done today. The use of FIS-B is very frequency efficient, due to that several ATIS can be sent on the same frequency.
4.4.4. Ground-based Regional Augmentation System
Ground-based Regional Augmentation System (GRAS) is a broadcast service that provides Global Navigation Satellite System 2 (GNSS) augmentation data to mobiles. GNSS augmentation is used to improve navigation, surveillance and airborne separation assurance in terms of accuracy, integrity, availability and continuity.
The method used when implementing GRAS, is to send DGNSS (Differential GNSS) correction messages from the ground station to all mobile GNSS users in its coverage area. The corrections are calculated by a system that consists of two GPS antennas/receivers that are located at two different but well-defined positions. The system compares the distance to each satellite, the pseudorange, according to the satellite almanac3 with the pseudorange measured by the two receivers. The calculated pseudorange-errors are then transmitted to all receivers so that they can correct their pseudoranges and get a more accurate position. The GRAS service can be divided into different service levels.
2 For example GPS (Global Positioning System)
3 The satellite almanac tells you where each satellite should be according to their orbit GRAS service level 1
Level 2
Level 3
Figure 4-3 GRAS service level 1, 2, 3 and 4 ref [9].
The different service levels can be used for several applications (Table 4-1) e.g. en-route, approach, landing and airport surface operations.
GRAS
service level Description Operation(s) Data volume
1 Integrity information En-route Low 2 Standard augmentation En-route / Terminal Area Medium 3 Advanced augmentation Approach and landing, airport surface operations High 4 Advanced augmentation Future critical operations High
5. Introduction to the VDL Mode 4/ADS-B technical equipment
The aim of this chapter is to briefly describe the technical equipment used for VDL Mode 4/ADS-B at Arlanda Airport, Sweden (see Figure 5-1 and Figure 5-2).
The VDL Mode 4/ADS-B system consists of (at least) one ground station on every equipped airport, one transceiver in every equipped vehicle (e.g. aircraft or car) and a ground network (that is not necessary for the system to work, but gives extended functionality).
5.1. Ground station
The VDL Mode 4 Ground station principally performs the following functions:
• Collecting ADS-B reports from equipped vehicles and distributing them to the Ground network (see chapter 4.4.1)
• Broadcasting TIS-B data (see chapter 4.4.2) • Broadcasting FIS-B data (see chapter 4.4.3)
• Generating and broadcasting GRAS data (see chapter 4.4.4)
Figure 5-2 Interior and location of the ground station at Arlanda airport
5.2. Transceiver
The VDL Mode 4/ADS-B transceiver (see Figure 5-3 and Table 5-1) mainly consists of a GPS-receiver, a VHF Transmitter and two VHF Receivers. The transceiver receives its position from the GPS-system and GRAS corrections (see chapter 4.4.4) from the ground station. After processing the data the transceiver broadcasts the position, velocity etc, in an ADS-B report, to other transceiver-equipped vehicles and to the ground station.
General
Power requirements 27.5 V DC 2 A GNSS Receiver 12 parallel channel
Transmitter specification Number of transmitters 1 Tuning range 112.000-136,975 MHz Channel spacing 25 kHz Frequency stability 0.0002% = 2 ppm TX to Rx turnaround time < 1 ms
Channel selection time < 13 ms
Baud rate 19200 bps
Modulation scheme GFSK
Carrier power (adjustable) 40 dBm into 50 Ω Adjacent Channel Power ICAO Annex 10 for VDL
Receiver specification Number of receivers Up to 4 Tuning range 108.000-136.975 MHz Channel spacing 25 kHz Frequency stability 0.0002% = 2 ppm Sensitivity -98 dBm CCI 10 dB Interfaces ARINC 429 Optional RS 232 or RS 422 3
Maintenance I/F RS 232/422 Yes
VHF Tx antenna 1
VHF Rx antenna 1
GNSS antenna 1
Physical characteristics
Form factor ATR 5.75“
Weight 2.8 kg
Cooling Not req.
Functions ADS-B Yes Point-to-point Yes DGNSS data Yes TIS-B Yes FIS-B Yes
Table 5-1 VDL Mode 4 Transceiver
5.3. Ground Network
The components included in the Ground Network are classified in a three level hierarchy. The Local Access Point Server (LAPS) at the lowest level followed by a Regional Access Point Server (RAPS) and at the top a Centralized Access Point Server (CAPS). Figure 5-4 below illustrates the network infrastructure.
Figure 5-4 Ground Network
A ground network implementation in Sweden could for example consist of one Ground station (two or more ground stations could be used at large airports) and one LAPS at every equipped airport. Further more every LAPS in northern Sweden could be connected to one RAPS and every LAPS in southern Sweden be connected to another RAPS. These two RAPS could be connected to one regional CAPS.
The main functions for the servers are: • The LAPS has three functions:
1. Receive ADS-B data and Keep-Alive data from the CNS Ground Stations 2. Filter duplicate ADS-B data
3. Forward ADS-B data to RAPS • The RAPS has two functions:
1. Filter duplicate ADS-B data received from different LAPS 2. Forward ADS-B data to the highest level, i.e. the CAPS • The CAPS has three functions:
1. Filter duplicate ADS-B data received from different RAPS
2. Handle connections to External Clients that wish to subscribe for ADS-B data. 3. Forward ADS-B to other CAPS (not yet implemented)
CAPS
Ground Station
NUP Ground Network for ADS-B data
CAPS RAPS RAPS LAPS LAPS Ground Station RAPS LAPS LAPS
6. Introduction to A-SMGCS
This chapter is based on ref [1] and [3].
Advanced Surface Movement Guidance and Control System (A-SMGCS) is the adopted term for the concept of an integrated aerodrome surface movement management system.
ICAO defines A-SMGCS as follows ref [1]:
“A-SMGCS is the term used to describe a modular system consisting of different
functions to support the safe, orderly and expeditious movement of aircraft and vehicles on aerodromes under all circumstances with respect to visibility conditions, traffic density and complexity of the aerodrome layout, taking into account the demanded capacity under various visibility conditions.”
or as:
“System providing routing, guidance, surveillance and control to aircraft and affected vehicles in order to maintain movement rate under all local weather conditions within the aerodrome Visibility Operational Level (AVOL) whilst maintaining the required level of safety.”
6.1. A-SMGCS System Description
The A-SMGCS system consists of four functional elements as described below (ref [3]): • Surveillance
Surveillance is the most fundamental function for any A-SMGCS. The aerodrome surface and the initial and final stages of flight should be covered by the surveillance function. The objective is that both identity and position should be provided for all traffic, including both aircraft and vehicles.
• Monitoring/alerting
The simplest form of monitoring/alerting consists of a situation display where the surveillance information is presented in a more complex A-SMGCS, automatic situation monitoring and alerting will be provided by the system, detecting runway incursions, taxiway alert situations and other hazardous scenarios.
• Guidance
Guidance can be performed manually by controllers using the surveillance and monitoring/alerting elements, or in more complex systems be fully or partially automated.
• Route planning
Route planning can be divided into strategic or tactical planning, where strategic planning can be done in advance. An example might be a plan for an aircraft to push back4 at a certain time. Tactical planning reacts in real time to the dynamics of the traffic situation. In an advanced system the route planning could be automated with the purpose to optimise the use of runway and taxiway resources.
A-SMGCS can be considered in several configuration levels. EUROCAE defines the configuration levels according to Table 6-1.
A-SMGCS
Configuration level Comprehensive surveillance monitoring/alertingAutomated Automated guidance Automated route planning
1 X 2 X X 3 X X X 4 X X X X
7. Requirements on A-SMGCS that VDL Mode 4/ADS-B should
fulfil
It is difficult to find general requirements for VDL Mode 4/ADS-B because different organisations have different requirements. The requirements stated in this report are primarily based on the system and the surveillance requirements in the ICAO document “European Manual on A-SMGCS”, ref [1]. Other sources have been used where the requirements in ref [1] has not been applicable or not satisfying. Requirements from more than one source are sometimes used to show that there are different opinions regarding that requirement.
The requirement that VDL Mode 4/ADS-B should fulfil are defined (if required, if not required marked with N/A) and after that divided into the three subheadings:
Subheading Purpose
Requirements State the requirement.
Verification Verify the VDL Mode 4/ADS-B system performance and describe the method used for the verification.
Validation Compare the system performance with the stated requirements.
To verify the performance of the VDL Mode/ADS-B system different tests and theoretical studies have been performed. Logging has been performed according to Figure 7-1 and Figure 7-2.
Figure 7-1 Simplified logging
Figure 7-1 shows a simplified logging arrangement. The purpose with this figure is to show that the logging of the ADS-B reports are made at the ground station, after been send over the VDL Mode 4 data link.
Transceiver Ground station LAPS CAPS VIP VIP FTP FTP FTP Data processing Data processing Data storing
Data compressing [WinRAR 3.10]
Data storing
Data decompressing [WinRAR 3.10]
Data decoding
SMTP
Data compressing [WinZIP 7.0]
Result Result
Data decompressing [WinZIP 7.0] Data processing PC/Linux SCAA decoding software PC/Windows Access Excel MATLAB PC/Windows Visualizing softwa re
Figure 7-2 Schematic logging
Figure 7-2 shows that the logging involves a lot of different computers, operative systems, programs and protocols.
7.1. Availability
Definition: Availability
The probability that a system or an item is in a functioning state at a given point in time. Ref [1], chapter 1.3
SCAA defines that the system is not available if (Critical failure):
1. the ground station fails to receive more than two consecutive ADS-B reports from the same transceiver situated on the manoeuvring area.
2. the ground station is not available for more than one second.
7.1.1. Requirements
The availability of an SMGCS (Surface Movement Guidance and Control System) should be sufficient to support the safe, orderly and expeditious flow of traffic on the movement area of an aerodrome down to its Aerodrome Visibility Operational Level (AVOL), ref [2], chapter 3.7.5.1.
The requirement for ADS-B data availability as stated by ICAO is 99.996 percent, ref [5], Appendix A, chapter 3.
The availability of the ADS-B system shall be 99.95%, ref [17].
7.1.2. Verification
To verify the availability, two transceivers have been placed on Arlanda Airport, Stockholm Sweden. For exact location see Figure 7-3. The transceivers have been configured to send 30 ADS-B reports per minute and frequency. This gives one ADS-B report per second when two frequencies are used. For detailed configurations and settings see Appendix A-1. The received ADS-B reports have been logged at the LAPS. A Cyclic Redundancy Check (CRC) is used to discover bit errors and assure the data link integrity. The CRC is an algorithm that creates a block of 16 bits that is added to the ADS-B message. The block contains information about the data in the message and is used to determine if the data is corrupted. The messages that have been sent but not processed by the ground station has either never been received or been discard due to the CRC check sum.
The availability has then been calculated in accordance to the definition of critical failure (see chapter 7.1) and the calculation methods described in Appendix B-1. This logging has been performed under several weeks with approximately the same result. The last two weeks of logging gives result according to Table 7-1.
Availability transceiver 1 [%] Availability transceiver 2 [%]
Week 1 99,97 98,01
Week 2 99,83 99,96
Table 7-1 Availability
7.1.3. Validation
The Availability requirements are not entirely fulfilled, but are fulfilled in some cases according to the requirement in ref [17]. These are not fully confirmed requirements and further tests are being performed to verify what availability VDL Mode 4 could obtain.
7.2. Integrity
Definition: Integrity
An attribute of a system or an item indicating that it can be relied upon to perform correctly on demand.
7.2.1. Requirements
The system design should preclude failures that result in erroneous data for operationally significant time periods, ref [1], chapter 3.7.3.1.
The Integrity for an ADS-B system shall be 10-7 on a per-report basis, ref [5], Appendix A, chapter 3. This
means that just one corrupt report out of 10 millions is allowed to pass thru the system.
7.2.2. Verification
A Cyclic Redundancy Check (CRC) is used to discover bit errors and assure the data link integrity. The CRC is an algorithm that creates a block of 16 bits that is added to the ADS-B message. The block contains information about the data in the message and is used to determine if the data is corrupted. A 16 bits CRC gives an integrity of 1.5⋅10−5.
7.2.3. Validation
The integrity provided by the 16 bits CRC is not good enough to meet the requirement 10-7 on a per report basis. A higher integrity can be achieved by one of the solutions described below.
The only solution that does not demand changes in the software is to monitor the data link through operational procedures. For example a cross checking with previous values for position, ground track, altitude etc, could be performed in order to detect abnormalities. The cross check would also detect faults that is not related to bit errors.
Other solutions can be to use a 24 bits CRC or even a Forward Error Correction (FEC) algorithm. FEC is much similar to CRC but it uses a different algorithm that makes it possible to corrected some errors. The 24 bits CRC gives an integrity of 6.0⋅10−8. The use of a FEC would not only give a higher integrity, it would
7.3. Continuity
Definition: Continuity
1. Continuity is the ability of an A-SMGCS to perform its required function without non-scheduled interruption during the intended operation in the A-SMGCS area, ref [1], chapter 5.7.4.1.
2. Continuity is defined as the probability that the data link can support the intended service over a defined exposure interval, given that the data link was operational (and could support the intended service) at the beginning of the exposure interval.
7.3.1. Requirements
The continuity probability of an ADS-B system shall be greater than 99.996 percent, ref [5], Appendix A, chapter 3.
The continuity of the ADS-B system shall be 99.98%, ref [17].
7.3.2. Verification
To verify the continuity, two transceivers have been placed on Arlanda Airport, Stockholm Sweden. For exact location see Figure 7-3. The transceivers have been configured to send 30 ADS-B reports per minute and frequency. This gives one ADS-B report per second when two frequencies are used. For detailed configurations and settings see Appendix A-2. The received ADS-B reports have been logged at the LAPS. The messages that have been sent but not processed by the ground station has either never been received or been discard due to the CRC check sum.
The continuity has than been calculated in accordance to the definition of critical failure (see chapter 7) and the calculation methods described in Appendix B-2. It has also been assumed that the critical time (exposure interval) is 15 seconds. This assumption is based on the time it takes for a vehicle to cross the runway and has been discussed with the air-traffic control.
The logging has been performed under several weeks with approximately the same result. The last two weeks of logging gives result according to Table 7-2.
Continuity Transceiver 1 [%] Continuity Transceiver 2 [%]
Week 1 99,86 99,85
Week 2 99,33 99,80
Table 7-2 Continuity
7.3.3. Validation
The continuity requirements are not fulfilled. The requirements for continuity are not fully confirmed and further tests are being performed to verify what continuity VDL Mode 4 could obtain.
7.4. Coverage
One definition of coverage used in radio communications is “The geographical area within which service
from a radio communications facility can be received.”
The coverage definition for ADS-B/VDL Mode 4 must be expanded to contain both VHF communication between the mobile transceiver and ground station and communication with GPS-satellites that gives sufficient positioning accuracy. This gives the following definition:
Definition: Coverage
The geographical area within which the mobile transceiver can have communication with at least one ground station and can receive GNSS information that gives sufficient positioning accuracy.
7.4.1. Requirements
The system should cover at least the movement area, ref [1], chapter 4.2.2.1.
Within the required area of the aerodrome, surveillance should be provided up to an altitude so as to cover missed approaches and low level helicopter operations, ref [1], chapter 3.5.1.4.
Surveillance should be provided for aircraft on approach to each landing runway direction, at such a distance that inbound aircraft can be integrated into an A-SMGCS operation and that aerodrome movements, including aircraft departures or aircraft crossing the relevant active runways can be managed, ref [1], chapter 3.5.1.5.
7.4.2. Verification
The test performed in order to determine how good the coverage of the system is at Arlanda Airport is presented in detail in Appendix A-3. Here follows a short description of the test procedure.
A vehicle equipped with a transceiver was driven around the major areas of the airport following the route displayed in
Figure 7-4. The data received at the ground station was logged.
The result from the test is plotted in Appendix C. The plot shows that all major areas of the airport are covered.
7.4.3. Validation
The test performed has shown that the coverage on ground is sufficient to support the use of ADS-B/VDL Mode 4 for surveillance at Arlanda airport. There has been no specific test to determine the coverage in approach and departure areas but results from tests performed in the Major terminal Area / En route in Kiruna, ref [15], chapter 12, indicates good coverage also in these area.
7.5. Capacity
Definition: Capacity
The System Capacity of an A-SMGCS is by ICAO defined as the maximum number of simultaneous movements of aircraft and vehicles that the system safely can support within an acceptable delay commensurate with runway and taxiway capacity at a particular aerodrome,
ref [3], chapter 3.1.2.
7.5.1. Requirements
The A-SMGCS should be able to handle all aircraft and vehicles that are covered by the A-SMGCS on the movement area at any instant in time, ref [1], chapter 4.2.3.1.
7.5.2. Verification
As mentioned in chapter 4.3, the VDL Mode 4 data link has 75 slots per second with a duration of 13.33 ms per slot. For ADS-B applications it is expected that a single position report from an aircraft will occupy one slot which gives that 75 positions could be updated every second. 75 slots per second give the possibility for
000 270 60 60
75⋅ ⋅ = reports per frequency channel to be sent during one hour.
7.5.3. Validation
The capacity of the ADS-B system is directly dependent on the update rate. A once per second update in all areas of the airport and for all vehicles is not necessary to maintain the safety. An example on a division of the airport with different update rates in different areas of the airport and for different vehicles can be found in Chapter 7.10. The divisions in that chapter are used to perform the following calculations. Some approximations about the rate of vehicles and movements on the airport have been done with the help of Air traffic controllers at Arlanda airport and they describe the situation during peak hour in the winter.
Vehicles:
70 vehicles with update rate 1 report every third second. 30 vehicles with update rate 1 report every second. Aircraft: 90 aircraft with no update (parked).
20 aircraft with update rate 1 report every second.
A vehicle with the update rate 1 report/ 3 seconds updates its position 1200 times during peak hour and a vehicle with update rate 1 report/ second updates its position 3600 times during peak hour. The total number of updates needed during peek hour is 70⋅1200+50⋅3600=264000reports. The VDL Mode 4 gives the possibility for 270 000 reports per frequency and hour. The capacity needed for the ADS-B service is 98% of the total capacity of one frequency. To be able to provide other services such as TIS-B, FIS-B and GRAS two frequencies are required. The use of two frequencies also gives other advantages, for example redundancy.
7.6. Velocity
Definition: Velocity
Velocity is the rate of change of displacement with time.
7.6.1. Requirements
The A-SMGCS should accommodate with sufficient accuracy all aircraft/vehicle velocities that will occur within the coverage area, ref [1], chapter 4.2.4.1.
Velocity accuracy: ±1 kts = 0.5 m/s, ref [1], chapter 4.2.4.5.
Should cover speeds between 0 and 250 kts = 128 m/s, ref [1], chapter 4.2.4.2.
7.6.2. Verification
The manufacturer of the GPS-receiver, Jupiter TU30-D400-021, in the transceiver claims the Velocity accuracy to be 0.1 m/s and that it can determine velocities up to 500 m/s. During the tests performed in this study, there has been nothing that indicates that the figures should be incorrect.
7.6.3. Validation
The Velocity accuracy of 0.1 m/s and cover up to 500 m/s claimed by the manufacturer is enough to fulfil the requirements. Since the performance stated by the manufacturer is much better than the requirement (5 times for accuracy and 4 times for coverage) and nothing during the tests performed has indicated differences, there has been decided not to perform any specific test to verify these figures.
7.7. Direction of movement
Definition: Direction of movement
Not Applicable
7.7.1. Requirements
The direction of movement should be determined with an accuracy of ±1°, ref [1], chapter 4.2.4.5.
7.7.2. Verification
The direction of movement was tested at Arlanda airport at the same time as the coverage test. The test was performed by driving a car along the centreline of the runway. This test was performed on all three runways. The car was equipped with a transceiver and the ADS-B messages were logged at the ground station. (For a detailed test procedure see appendix A-6) Analysing the logged data gives that the deviation from the direction of the runways has an average of 0,16 degrees and a maximum of 0,62 degrees.
7.7.3. Validation
The maximum deviation of 0,62 degrees and the average deviation of 0,16 degrees fulfil the requirement of ±1 degree.
7.8. Reference point
Definition: Reference point
The reference point is very important if the air traffic control should be able to separate aircrafts and vehicles on the ground. The ADS-B report includes only the position of the GPS antenna, which is not the same on all vehicles and aircraft.
7.8.1. Requirements
The reference point should be the centre of the aircraft or the vehicle, the mid-point of the longitudinal axis,
ref [1], chapter 4.3.2.2.
7.8.2. Verification
The ADS-B report includes the GPS antenna position, if this is known simple calculations can be used to determine the reference point. This can be done before the position is presented in the ATC.
7.8.3. Validation
The requirement of a defined reference point is more of an operational requirement (not in scope of this work) than a technical. It would not be any difficulties to fulfil with an ADS-B based surveillance system.
7.9. The Reported Position Accuracy
Definition: The Reported Position Accuracy
The difference at a specified confidence level, between the reported position of the target and the actual position of the target at the time of report, ref [3], chapter 3.2.1.2.
7.9.1. Requirements
The actual position of an aircraft, vehicle or obstacle on the surface should be determined within a horizontal radius of 7.5m, ref [1], chapter 4.3.3.1.
Altitude of aircraft when airborne should be determined within ± 10m, ref [1], chapter 4.3.3.2.
7.9.2. Verification
To verify the position accuracy, two different tests have been performed, one static and one dynamic. Here follows a short description of each of the two test methods. For a more detailed description see Appendix A-4 (dynamic) and Appendix A-5 (static).
7.9.2.1. Dynamic
To determine the position accuracy of a moving object, a dynamic test was performed. With the RTK (Real Time Kinematics) equipment a test track (Figure A-1) was produced and the certain positions where defined. A vehicle equipped with a transceiver was driven according to the test track and the ADS-B messages from the transceiver were logged at the ground station.
7.9.2.2. Static
In the static test, one transceiver was placed on location 1 in Figure 7-5. The position of the transceiver was defined with a RTK equipment to have a good reference point (down to seconds of a degree). After the position were defined the transceiver were left on the location for one week during which the ADS-B messages from the transceiver were logged at the ground station.
Figure 7-5 Locations of the transceivers.
The information from the static position accuracy tests was processed according to the calculation methods in appendix B and gave the results according to Table 7-3 and Figure 7-6. Maximum error measured is 15 meters.
Measurements [%] Within a horizontal radius [m]
99,99 7,5 99 4,8 95 3,6
Table 7-3 Horizontal radius error
-2 0 2 4 6 8 10 12 14 16 0 0.5 1 1.5 2 2.5 3x 10 5
Horizontal radius error [m]
F
requ
enc
y
Histogram
Figure 7-6 Histogram horizontal radius error
Figure 7-7 Reported positions plot
Figure 7-7 shows the reported positions as dots and the cross shows the actual position of the transceiver. Note that every dot could represent several ADS-B reports.
7.9.3. Validation
• Dynamic Coming in next version.
• Static
7.10. Update
Definition: Update
A renewal of target reports relating to all targets under surveillance, ref [3], chapter 1.3.
7.10.1. Requirements
All targets under surveillance should be updated at least every second, ref [1], chapter 4.3.5.1.
7.10.2. Verification
The VDL Mode 4 standard supports an update rate up to 60 reports/minute and frequency. 60 reports/minute equals an update rate of once every second (60 / 60 = 1).
7.10.3. Validation
The requirement of 1 report at least every second can be fulfilled with a VDL Mode 4 based A-SMGCS.
7.11. Latency
Definition: Latency
Latency is the time between when the position for the affected vehicle is valid and the time when the position is monitored in the ATC.
7.11.1. Requirements
The latency and validation of surveillance position data for relevant aircraft and vehicles should not exceed 1 second, ref [1], chapter 4.3.5.2.
The latency and validation of identification data for relevant aircraft and vehicles should not exceed 3 seconds, ref [1], chapter 4.3.5.3.
7.11.2. Verification
The latency from when the position is valid until it is sent to the ATC can be divided into the following parts:
Part time Definition of part time Note Latency [seconds]
Data age The time from when the position is valid until it is sent from the transceiver.
Data age is a standard parameter defined in VDL
Mode 4/ADS-B. 1,5 Propagation time The time from when the
ADS-B message is sent from the mobile transceiver until it is received at the ground station transceiver.
Data processing time in
the ground station The time from when the message is received until it is sent to the ATC.
0,1
Note: The latency between ground station and when the position is monitored in the ATC is not in the scope of this report but should be included in the total latency.
Data age is approximately 1,5 seconds. Propagation time and data processing time in the ground station is approximately 0,1 seconds, this gives a total latency of 1,6 seconds, the latency between the ground station and when the position is monitored in the ATC is not included.
7.11.3. Validation
The requirements (1 second) on latency and validation of surveillance position data for relevant aircraft and vehicles are not fulfilled.
The requirements (3 seconds) on latency and validation of identification data for relevant aircraft and vehicles are fulfilled. Latency between ground station and when the position is monitored in the ATC is not included.
7.12. Surveillance Detection
Definition: Surveillance Detection
N/A
7.12.1. Requirements
The surveillance function should be capable of detecting aircraft, vehicles and obstacles.
Methods should be employed to reduce to a minimum adverse effect as signal reflection and shadowing.
7.12.2. Verification
Every aircraft and vehicle equipped with a transceiver would be detected by the surveillance system. The transceiver sends identification and position with regular intervals.
7.12.3. Validation
The requirement of detecting aircraft and vehicles are fulfilled. The requirement of detecting obstacles is not fulfilled.
8. Failure Mode, Effects and Criticality Analysis (FMECA)
Failure Mode, Effects and Criticality Analysis (FMECA) is a method of reliability analyse intended to identify failures that have significant consequences and effects on the system performance in the application considered.
This FMECA follows ref [11], which is a standard document published by IEC (International Electrotechnical Commission).
8.1. Scope of FMECA
This FMECA includes failure modes that affect the transceiver, the ground station and the data link between the transceiver and the ground station. The transceiver and the ground station are being seen as black boxes that either works properly or not. A FMECA for the transceiver has been done in ref [12] and for the ground station in ref [15].
Figure 8-1 Scope of FMECA
8.2. Contents of FMECA
The FMECA consists of a number of different elements described below. • Equipment name
The name of the system element under analysis. • Function
Function performed by the system element. • Identity number
Identification number used for cross-references. • Failure modes
A failure mode is the effect by which a failure is observed in a system component. • Failure causes
The possible causes associated with each failure mode are identified and described. • Failure effect
The failure effect is divided into: o Local effect
The expression local effects refers to the effects of the failure mode on the system element under consideration.
o End effect
End effect describes the failure effect on the highest system level that is defined and evaluated in the FMECA.
• Failure detection
The method for detection of the failure mode is described. • Alternative provisions
Identification and evaluation of any design features at a given system level for other provisions to prevent or reduce the effect of the failure mode.
• Failure probability
The probability of failure are divided into four levels: o Very low
o Low o Medium o High
Note: The failure probability in this FMECA is only estimations and would need to be reworked in a future safety case.
• Criticality level
Not in scope of document. • Remarks
8.3. FMECA for ADS-B/VDL Mode 4
Failure effect Equipment
name Function Identity number Failure mode Failure cause Local effect End effect
Failure
detection Alternative provisions probability Failure Criticality level Remarks Mobil transceiver GNSS-antenna Provides transceiver with GNSS-data 1. No input from GNSS- antenna Cable
breakdown No position finding on own vehicle Loss of position finding on affected vehicle See chapter
9.1 N/A Low Not in scope of document N/A
2. Contact fault No position
finding on own vehicle Loss of position finding on affected vehicle See chapter
9.1 N/A Low Not in scope of document N/A
3. Covered
antenna No position finding on own vehicle Loss of position finding on affected vehicle See chapter
9.1 N/A Low Not in scope of document N/A
Transceiver GNSS data Provides transceiver with GNSS-data 4. No GNSS-data No GNSS satellites in view No position finding on own vehicle Loss of position finding on affected vehicle See chapter 9.2
N/A Low Not in scope
of document N/A 5. GNSS system down No position finding on own vehicle Loss of position finding on affected vehicle See chapter
9.2 N/A Very low Not in scope of document N/A
6. Not correct
GNSS-data Wrong data from GNSS-satellites Wrong position finding on own vehicle Not correct position finding on affected vehicle See chapter
9.3 N/A Very Low Not in scope of document N/A
Mobile transceiver VHF-antenna Provides communication between mobile and ground station 7. No input from VHF-antenna Cable breakdown No communication with ground station No communication between ground station and affected mobile See chapter
