VDL Mode 2 Capacity and Performance Analysis

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November 2015

VDL Mode 2 Capacity and Performance

Analysis

1. Introduction:

The objective of this paper is to deliver the background and results of the SESAR Joint Undertaking (SJU) study on VDL Mode 2 Capacity and Performance Analysis.

2. Background:

High quality data communications capabilities, consistent and dependable, are essential enablers to support the implementation of efficiency and capacity improvements required by the Single European Sky.

The mandated solution in Europe, Regulation (EC) No29/2009 as amended by Implementing Regulation (EU) 2015/310, is based on VDL mode 2 technology. However, as the operational use of VDL mode 2 for ACARS and CPDLC using ATN was progressively reaching the intended operational usage, certain performance degradation issues were observed that raised concerns on the overall usability of the system. These concerns led the European Commission to request EASA to investigate into the observed performance issues of this technology. The resulting EASA report included a ten point Action Plan involving proposals for simulations, performance assessment campaigns, flight trials and deployment planning needed before an informed decision on the future of VDL 2 implementation could be done.

In this context, the SJU launched two projects focusing on VDL Mode 2:

The “VDL Mode 2 Capacity and Performance Analysis” is an SJU initiative launched prior to the EASA investigation. It was conducted between June 2014 and July 2015. The main objective of the study was the identification of the time horizon by which VDL Mode 2 (assuming usage of up to 4 frequencies) should reach its operational limits in Europe. The study was performed by a consortium led by ENAV depicted in figure 1.

Figure 1: "VDL Mode 2 Capacity and Performance Analysis "Consortium

The results and conclusions are detailed in section 3 whilst the final report is available in the attachment (section 4). The strategic aim of this study was to assess the capability of VDL2 to support SESAR services on the long term and to determine the point in time by which the next generation datalink technology should be available.

The “VDL Mode 2 Measurement, Analysis, Testing and Simulation Campaign” (also referred to as the ELSA Consortium study) was launched by the SJU further to a European Commission request. It addresses the EASA recommendations 1 to 6 related to the identification of the problem root cause and the provision of potential fixes. It aims at further analyzing the end to end VDL Mode 2 issues experienced today (through simulation and flight testing campaigns), defining potential technical solutions for multi-frequency deployment and VDL Mode 2 potential improvement (protocol optimization, etc.). The project started in February 2015 and is due to deliver the final report mid-2016. It is performed by a consortium led by NATS and actively involving a wide representation of stakeholders. The consortium is depicted hereafter in figure 2.

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Figure 2: ELSA Consortium

3. Main findings of the VDL Mode 2 Capacity and Performance Analysis:

This section gives an overview of the VDL Mode 2 Capacity and Performance Analysis. It aims at and providing guidance on the interpretation of the results.

How to read the results:

The results of the capacity study are based on assumptions, detailed within the document, proposed by the consortium as representing the most realistic scenarios until 2040. The VDL Mode 2 protocol considered was the one currently used by many European ANSPs/CSPs and required by the European Commission Regulation (EC) No 29/2009 requirements on data link services for the Single European Sky. Multi-Frequency options are proposed by the consortium, in terms of frequencies usage for better utilization of the four VDL Mode 2 channels. The ongoing ELSA study is expected to further develop the Multi-Frequency options and to conclude within its report on the final Multi-Multi-Frequency solution.

It should be noted that the results of the study are valid within these assumptions. Dates where the VDL2 should reach the capacity limits highly depend on implementation options and on technical configurations. Changes to these assumptions (e.g., change of topology, introduction of more than 4 frequencies, and use of a complementary media to VDL2) are likely to impact the results.

The main findings:

Looking to a time window from “2015” until “2040” and considering various traffic growth expectations in Europe, the study defined the expected growth of ATS and AOC datalink traffic over that period. Based on in depth modelling of all the Air and Ground components, the simulation determined the VDL Mode 2 performance at the network level and also at each individual Ground Station level. The results enabled conclusions on where and when the VDL Mode 2 link would suffer from quality degradation making it no longer usable especially for ATS purposes.

The main conclusions and recommendations that emerge from this report are summarized hereafter.

These conclusions represent the main outcome of the VDL Mode 2 Capacity and Performance Analysis study and do not represent formal recommendations to the European Commission on the next steps.

o VDL2 over one single frequency would already reach its capacity limits in 2015. Therefore, Multi-frequency deployment in Europe is a “MUST” as of today (2015).

o A 4 frequencies implementation is a minimum requirement to support VDL2 deployment until 2025 in high density area.

o Further optimisation options under investigation by ELSA may extend the viability of VDL2 over 4 frequencies beyond 2025 in high density area.

o It is highly recommended to anticipate the evolution of the European datalink infrastructure in the ATM masterplan and to prioritize the development of the next generation datalink technology within SESAR.

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November 2015

4. The report:

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Performance Analysis

Document information

Project Title VDL Mode 2 Capacity and Performance Analysis Project Number SESAR_CFT_0096

Project Manager ENAV

Deliverable Name VDL Mode 2 Capacity and Performance Analysis Deliverable ID SESAR_CFT_0096

Edition 00.01.06 Template Version 03.00.00 Task contributors

ENAV (Project Manager of the consortium), University of Salzburg, ENAIRE, DFS, NATS, LFV and supported by: DSNA, EasyJet, Air France, Lufthansa, SITA and Airbus.

Abstract

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VDL Mode 2 Capacity and Performance Analysis

Authoring & Approval

Prepared By - Authors of the document.

Name & Company Position & Title Date Michele Carandente / ENAV Project Manager 26/05/2015 Carl-Herbert Rokitansky / Uni of Salzburg Project Member 26/05/2015 Reviewed By - Reviewers internal to the project.

Name & Company Position & Title Date Michele Carandente / ENAV Project Manager 26/05/2015 Carl-Herbert Rokitansky / Uni of Salzburg Project Member 26/05/2015 Jan Stibor / LFV Project Member 26/05/2015 Jerome Condis / Airbus Project Member 08/05/2015 Marc Speltens / SITA Project Member 08/05/2015 Luc Rochard / AirFrance Project Member 22/05/2015 Alan Pirovano / ENAC Reviewer 10/07/2015

Approved for submission to the SJU By - Representatives of the company involved in the project. Name & Company Position & Title Date Michele Carandente / ENAV Project Manager 26/05/2015 Carl-Herbert Rokitansky / Uni of Salzburg Project Member 26/05/2015 Raphael Pascal / Airbus Project Member 05/06/2015 Mario Garcia / ENAIRE Project Member 03/06/2015 Armin Schlereth / DFS Project Member 08/06/2015 Jan Stibor / LFV Project Member 26/05/2015 Marc Speltens / SITA Project Member 28/05/2015 Alan McNab / NATS Project Member 08/06/2015

Document History

Edition Date Status Author Justification

00.00.03 28/04/2015 Draft M.Carandente Monofrequency outputs 00.00.04 29/04/2015 Draft M.Carandente Refinement of the strawman 00.00.08 12/05/2015 Draft C.-H. Rokitansky Summary of Results 00.00.14 20/05/2015 Draft C.-H. Rokitansky Multi-Frequency results and

Update 00.01.00 26/05/2015 Draft M. Carandente Proposed Final

00.01.01 08/06/2015 Final M. Carandente Added reviews from partners 00.01.03 06/08/2015 Final

M. Carandente Max Ehammer C.-H. Rokitansky

Resolution of external comments (EASA, ECTL, ENAC, etc.)

00.01.04 07/08/2015 Final M. Carandente General review of the document

00.01.05 07/09/2015 Final M. Carandente Acknowledgement

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List of tables

Table 1 - SITA Ground Stations ... 21

Table 2 - ARINC Ground Stations ... 22

Table 3 - ENAV Ground Stations ... 22

Table 4 - Network subscription rate assumptions ... 22

Table 5 - Aircraft equipage rate assumptions ... 23

Table 6 - Frequency management assumptions... 24

Table 7 - Equipage rate with respect to all simulated flights ... 27

Table 8 - Alternative communication means assumptions ... 27

Table 9 - Brief resume of main assumptions ... 34

Table 10: Summary of parameter settings for simulation stream 01 – as discussed previously. ... 35

Table 11: Single Frequency (SF) Scenario compilation ... 35

Table 12: Summary of parameter settings for simulation stream 02 – as discussed previously. ... 36

Table 13: Multi Frequency Scenario compilation ... 36

Table 14 - Capacity Limitations values, Single-Frequency (SF), optimistic traffic growth, high traffic area ... 39

Table 15 - TRTD values, Single-Frequency (SF), optimistic traffic growth, high traffic area ... 40

Table 16 - Overall results, Single-Frequency (SF), optimistic traffic growth, high traffic area ... 40

Table 17 - Capacity Limitation values, Single-Frequency (SF), optimistic traffic growth with AOC Migration, high traffic area ... 41

Table 18 - TRTD values, Single-Frequency (SF), optimistic traffic growth with AOC migration, high traffic area ... 42

Table 19 – Overall results, Single-Frequency (SF), optimistic traffic growth with AOC migration, high traffic area ... 42

Table 20 - Capacity Limitations values, Single-Frequency (SF), median traffic growth, high traffic area ... 43

Table 21 - TRTD values, Single-Frequency (SF), median traffic growth, high traffic area ... 44

Table 22 – Overall results, Single-Frequency (SF), median traffic growth, high traffic area ... 44

Table 23 - Capacity Limitation values, Single-Frequency (SF), optimistic traffic growth with AOC Migration, high traffic area ... 45

Table 24 - TRTD values, Single-Frequency (SF), median traffic growth with AOC migration, high traffic area ... 46

Table 25 – Overall results, Single-Frequency (SF), median traffic growth with AOC migration, high traffic area ... 46

Table 26 - Capacity Limitation values, Single-Frequency (SF), optimistic traffic growth, medium traffic area ... 47

Table 27 - TRTD values, Single-Frequency (SF), optimistic traffic growth, medium traffic area ... 48

Table 28 – Overall results, Single-Frequency (SF), optimistic traffic growth, medium traffic area ... 48

Table 29 - Capacity Limitation values, Single-Frequency (SF), optimistic traffic growth with AOC Migration, medium traffic area ... 49

Table 30 - TRTD values, Single-Frequency (SF), optimistic traffic growth with AOC Migration, medium traffic area ... 50

Table 31 – Overall results, Single-Frequency (SF), optimistic traffic growth with AOC Migration, medium traffic area ... 50

Table 32 - Capacity Limitation values, Single-Frequency (SF), median traffic growth, medium traffic area ... 51

Table 33 - TRTD values, Single-Frequency (SF), median traffic growth, medium traffic area ... 52

Table 34 – Overall results, Single-Frequency (SF), median traffic growth, medium traffic area ... 52

Table 35 - Capacity Limitation values, Single-Frequency (SF), median traffic growth with AOC Migration, medium traffic area ... 53

Table 36 -TRTD values, Single-Frequency (SF), median traffic growth with AOC Migration, medium traffic area ... 54

Table 37 – Overall results, Single-Frequency (SF), median traffic growth with AOC Migration, medium traffic area ... 54

Table 38 - Capacity Limitation values, SF, Multi-Frequencies, optimistic traffic growth, high traffic area ... 60

Table 39 – TRTD values, SF, Multi-Frequencies, optimistic traffic growth, high traffic area ... 60

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Table 41 - Capacity Limitation values, SF, Multi-Frequencies, optimistic traffic growth with AOC

migration, high traffic area ... 63

Table 42 - TRTD values, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, high traffic area ... 63

Table 43 – Overall results, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, high traffic area ... 64

Table 44 - Capacity Limitation values, SF, Multi-Frequencies, median traffic growth, high traffic area ... 66

Table 45 - TRTD values, SF, Multi-Frequencies, median traffic growth, high traffic area ... 66

Table 46 – Overall results, SF, Multi-Frequencies, median traffic growth, high traffic area ... 67

Table 47 - Capacity Limitation values, SF, Multi-Frequencies, median traffic growth with AOC migration, high traffic area ... 69

Table 48 - TRTD values, SF, Multi-Frequencies, median traffic growth with AOC migration, high traffic area ... 69

Table 49 – Overall results, SF, Multi-Frequencies, median traffic growth with AOC migration, high traffic area ... 70

Table 50 - Capacity Limitation values, SF, Multi-Frequencies, optimistic traffic growth, medium traffic area ... 72

Table 51 – TRTD values, SF, Multi-Frequencies, optimistic traffic growth, medium traffic area ... 72

Table 52 – Overall results, SF, Multi-Frequencies, optimistic traffic growth, medium traffic area ... 73

Table 53 - Capacity Limitation values, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, medium traffic area ... 75

Table 54 - Capacity Limitation values, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, medium traffic area ... 75

Table 55 – Overall results, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, medium traffic area ... 76

Table 56 - Capacity Limitation values, SF, Multi-Frequencies, median traffic growth, medium traffic area ... 78

Table 57 - TRTD values, SF, Multi-Frequencies, median traffic growth, medium traffic area ... 78

Table 58 – Overall results, SF, Multi-Frequencies, median traffic growth, medium traffic area ... 79

Table 59 - Capacity Limitation values, SF, Multi-Frequencies, median traffic growth with AOC migration, medium traffic area ... 81

Table 60 - TRTD values, SF, Multi-Frequencies, median traffic growth with AOC migration, medium traffic area ... 81

Table 61 – Overall results, SF, Multi-Frequencies, median traffic growth with AOC migration, medium traffic area ... 82

Table 62: Expected number of flights of mobility scenarios from 2015 to 2040 ... 132

Table 63: Evaluated SITA network relevant for area of interest with high data link usage ... 134

Table 64: Evaluated ARINC network relevant for area of interest with high data link usage ... 134

Table 65: Evaluated SITA & ARINC network relevant for area of interest with low data link usage .. 135

Table 66: Parameters used for link budget calculation. ... 137

Table 67: Frequency Option 1: Single frequency. ... 137

Table 68: Frequency Option 2: Multi frequency deployment with two frequencies. ... 138

Table 69: Frequency Option 3: Multi frequency deployment with three frequencies. ... 138

Table 70: Frequency Option 4: Multi frequency deployment with four frequencies. ... 138

Table 71: ATS Communication profile B2 / B3 ... 142

List of figures

Figure 1 - Existing and possible future communication systems aligned with SESAR deployment ... 15

Figure 2 - High Level view of simulation tool chain ... 17

Figure 3 - Traffic Growth within ECAC Area ... 19

Figure 4 - European VDL Mode 2 GS topology and simulated reference area ... 20

Figure 5 - Number of flights within selected areas of interest ... 21

Figure 6 - Peak instantaneous aircraft count (PIAC) for the ECAC region ... 23

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Figure 8 - AOC percentage (%) – whole simulation zone (30N010W – 60N025E) – Optimistic Traffic

... 28

Figure 9 - AOC with migration % – whole simulation zone (30N010W – 60N025E) – Optimistic Traffic ... 28

Figure 10 - ATS and AOC data – High Traffic Area (Lille) – Optimistic Traffic (ScA) ... 28

Figure 11 - AOC percentage (%) – High Traffic Area (Lille) – Optimistic Traffic (ScA) ... 29

Figure 12 - AOC with migration % – High Traffic Area (Lille) – Optimistic Traffic (ScA) ... 29

Figure 13 - ATS and AOC data – Medium Traffic Area (Rome) – Optimistic Traffic (ScA) ... 29

Figure 14 - AOC percentage (%) – Medium Traffic Area (Rome) – Optimistic Traffic (ScA) ... 30

Figure 15 - AOC with migration % – Medium Traffic Area (Rome) – Optimistic Traffic (ScA) ... 30

Figure 16 - ATS and AOC data – whole simulation zone (30N010W – 60N025E) – Median Traffic .... 30

Figure 17 - AOC percentage (%) – whole simulation zone (30N010W – 60N025E) – Median Traffic . 31 Figure 18 - AOC with migration % – whole simulation zone (30N010W – 60N025E) – Median Traffic ... 31

Figure 19 - ATS and AOC data – High Traffic Area (Lille) – Median Traffic Growth (ScC) ... 32

Figure 20 - AOC percentage (%) – High Traffic Area (Lille) – Median Traffic Growth (ScC) ... 32

Figure 21 - AOC with migration % – High Traffic Area (Lille) – Median Traffic Growth (ScC) ... 32

Figure 22 - ATS and AOC data – Medium Traffic Area (Rome) – Median Traffic Growth (ScC) ... 33

Figure 23 - AOC percentage (%) – Medium Traffic Area (Rome) – Median Traffic Growth (ScC) ... 33

Figure 24 - AOC with migration % – Medium Traffic Area (Rome) – Median Traffic Growth (ScC) .... 33

Figure 25 - Capacity Limitations, Single-Frequency (SF), optimistic traffic growth, high traffic area ... 39

Figure 26 - Capacity Limitations, Single-Frequency (SF), optimistic traffic growth with AOC Migration, high traffic area ... 41

Figure 27 - Capacity Limitations, Single-Frequency (SF), median traffic growth, high traffic area ... 43

Figure 28 - Capacity Limitations, Single-Frequency (SF), median traffic growth with AOC Migration, high traffic area ... 45

Figure 29 - Capacity Limitations, Single-Frequency (SF), optimistic traffic growth, medium traffic area ... 47

Figure 30 - Capacity Limitations, Single-Frequency (SF), optimistic traffic growth with AOC Migration, medium traffic area ... 49

Figure 31 - Capacity Limitations, Single-Frequency (SF), median traffic growth, medium traffic area 51 Figure 32 - Capacity Limitations, Single-Frequency (SF), median traffic growth with AOC Migration, medium traffic area ... 53

Figure 33 –VDL Mode 2 ground station network performance - Single Frequency scenarios – years 2015, 2020, 2025, 2030, 2035 and 2040 ... 56

Figure 34 –VDL Mode 2 ground station network performance - Single Frequency scenarios – years 2015, 2020, 2025, 2030, 2035 and 2040 ... 58

Figure 35 - Capacity Limitations, SF, Multi-Frequencies, optimistic traffic growth, high traffic area .... 59

Figure 36 - Capacity Limitations, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, high traffic area ... 62

Figure 37 - Capacity Limitations, SF, Multi-Frequencies, median traffic growth, high traffic area ... 65

Figure 38 - Capacity Limitations, SF, Multi-Frequencies, median traffic growth with AOC migration, high traffic area ... 68

Figure 39 - Capacity Limitations, SF, Multi-Frequencies, optimistic traffic growth, high traffic area .... 71

Figure 40 - Capacity Limitations, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, medium traffic area ... 74

Figure 41 - Capacity Limitations, SF, Multi-Frequencies, median traffic growth, medium traffic area . 77 Figure 42 - Capacity Limitations, SF, Multi-Frequencies, median traffic growth with AOC migration, medium traffic area ... 80

Figure 43: VDL Mode 2 GS network performance – Optimistic Traffic - Single- (SF) and Multi-Frequency scenarios: FO2, FO3, FO4, MF4 – Year 2015 ... 84

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Figure 48: VDL Mode 2 GS network performance – Optimistic Traffic - Single- (SF) and

Multi-Frequency scenarios: FO2, FO3, FO4, MF4 – Year 2040 ... 90

Figure 49: VDL Mode 2 GS network performance – Median Traffic - Single- (SF) and Multi-Frequency scenarios: FO2, FO3, FO4, MF4 – Year 2020 ... 91

Figure 54 - VDL Mode 2 GS network performance – Optimistic Traffic - Single- (SF) and

Figure 65 - Capacity Limitations and TRTD values, SF, Multi-Frequencies, optimistic traffic growth, high traffic area ... 110

Figure 66 - Overall results, Single-Frequency (SF), optimistic traffic growth, high traffic area ... 110

Figure 67 - Capacity Limitations and TRTD values, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, high traffic area ... 110

Figure 68 – Overall results, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, high traffic area ... 110

Figure 69 - Capacity Limitations and TRTD values, SF, Multi-Frequencies, medium traffic growth, high traffic area ... 111

Figure 70 – Overall results, SF, Multi-Frequencies, median traffic growth, high traffic area ... 111

Figure 71 - Capacity Limitations and TRTD values, SF, Multi-Frequencies, medium traffic growth with AOC migration, high traffic area ... 112

Figure 72 – Overall results, SF, Multi-Frequencies, median traffic growth with AOC migration, high traffic area ... 112

Figure 73 - High Traffic Area - ARINC Stations – Baseline Year 2014/15 ... 113

Figure 74 - High Traffic Area - SITA Stations – Baseline Year 2014/15 ... 113

Figure 75 - Capacity Limitations and TRTD values, SF, Multi-Frequencies, optimistic traffic growth, medium traffic area ... 115

Figure 76 – Overall results, SF, Multi-Frequencies, optimistic traffic growth, medium traffic area ... 115

Figure 77 - Capacity Limitations and TRTD values, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, medium traffic area ... 116

Figure 78 – Overall results, SF, Multi-Frequencies, optimistic traffic growth with AOC migration, medium traffic area ... 116

Figure 79 - Capacity Limitations and TRTD values, SF, Multi-Frequencies, medium traffic growth, medium traffic area ... 116

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Figure 80 – Overall results, SF, Multi-Frequencies, median traffic growth, medium traffic area ... 116

Figure 81 - Capacity Limitations and TRTD values, SF, Multi-Frequencies, medium traffic growth with AOC migration, medium traffic area ... 117

Figure 82 – Overall results, SF, Multi-Frequencies, median traffic growth with AOC migration, medium traffic area ... 117

Figure 83 – Comparison of Offered Load for various scenarios – High traffic vs. Medium traffic area ... 118

Figure 84 - Medium Traffic Area - ENAV Stations – Baseline Year 2014/15 ... 118

Figure 85 - Work Breakdown Structure ... 121

Figure 86 - GANTT of the project ... 127

Figure 87: High Level view of simulation tool chain ... 128

Figure 88: Number of Flights within ECAC Area (peak day 2014; 2015 to 2050 (forecast)) ... 132

Figure 89: Number of flights on reference day (Aug. 29th 2014). ... 133

Figure 90: Simulated area including areas of interest with high and low data traffic. ... 134

Figure 91: Interference ... 136

Figure 92: Possible trigger events of a simulated flight. ... 139

Figure 93: Application instance and corresponding dialogues. ... 140

Figure 94: Calculation of maximum execution time for a dialogue ... 140

Figure 95: AOC application message exchanges for different subscriber levels. ... 143

Figure 96 - AOC messages assumed to be exchanged between air and ground for the years 2020 to 2040 ... 145

Figure 97: Markov Model to estimate Technical Round Trip Delay (TRTD) for end-to-end data traffic. ... 147

Figure 98: Simulation protocol stack of VDL Mode 2 performance and capacity study ... 149

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High quality data communications capabilities, consistent and dependable, are essential enablers to support the implementation of the Single European Sky.

The Commission Regulation (EC) No 29/2009, which lays down the requirements on Data Link Services for the Single European Sky (also known as the Data Link Regulation), entered into force on 6 February 2009, became applicable from 7 February 2013 and has subsequently been amended in February 2015. Its essential objective was to increase Air Traffic Control capacity by supplementing voice communication by air-ground data link communications. It addresses both the airborne and ground environment with obligations of data link capability for both operators of aircraft and air navigation service providers (ANSP's).

The mandated solution is based on VDL mode 2 technology. However, as the use of VDL mode 2 for ACARS over AVLC (AOA) and CPDLC using ATN has become more widespread, certain performance issues were observed that raised concerns on the usability of the system. These concerns led the European Commission to sponsor an EASA investigation into the observed performance issues of this technology. The resulting final report included a ten point Action Plan involving proposals for simulations, performance assessment campaigns, flight trials and deployment planning.

SJU launched two studies focussing on VDL Mode 2: the first one “the Capacity and Performance Analysis”, covered by this document, is dealing with the identification of the time horizon by which VDL Mode 2 should reach its operational limits in Europe, while the second study “VDL Mode 2 Measurement, Analysis” aims at further analysing the end to end VDL Mode 2 issues experienced today (through lab and flight testing campaigns) and to define potential technical solutions for multi-frequency deployment and VDL Mode 2 improvement (protocol optimization, etc). Both studies are complementary coordinated together.

The objective of the “VDL Mode 2 Capacity and Performance Analysis”, presented here, is the identification of the limits of the operational performance of VDL Mode 2 in terms of the Comparison Throughput to Offered Load and its operational usage for ATS purposes. Since the VDL mode 2 technology provides neither the mechanisms for separation of ATS and AOC traffic nor a prioritization scheme for messages with respect to parameters such as safety criticality, it is an accepted consensus that in its current implementation, the technology will at some point reach the limit of its usefulness as a technology from an ATC point of view. Air Traffic Management requires a robust, responsive and trustable datalink technology to help offload traffic off existing voice R/T channels whilst at the same time increasing the overall level of air safety.

Currently VDL Mode 2 is operating over one single VHF frequency. From a technical viewpoint, the study sought to reveal whether and if so, at what point, the VDL Mode 2 link, operating on up to 4 VHF frequencies, will reach a performance level commensurate with degradation of service that would objectively be judged as unacceptable for the purposes of the provision of ATC services. The reference document used for this evaluation is CFC/Datalink/PMP "Link 2000+ DLS CRO Performance Monitoring Requirements", Eurocontrol / Network Manager Directorate, David Isaac, Ed. 1.3, 19 May 2014.

Looking to a time window from “2015” until “2040” and considering various traffic growth expectations in Europe, the study defined the expected growth of ATS and AOC datalink traffic over that period. Based on in depth modelling of all the Air and Ground components, the simulation determined the VDL Mode 2 performance at the network level and also at each individual Ground Station level. The results enabled conclusions on where and when the VDL Mode 2 link would suffer from quality degradation making it no longer usable especially for ATS purposes.

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A cross-year analysis has also been detailed, to provide an understanding of how the VDL Mode 2 datalink performances will decrease in comparison to increases of usage.

Two areas of interest have been deeply analysed, one representing the busiest airspace in Europe (including London, Paris and Brussels airports and centred on Lille) and an area with medium traffic (centred around Rome).

The topology model for this simulation reflects the existing geographical location of the Ground Stations (GS) in Europe. Although, the simulation did not consider the geographical redistribution of the stations, performance details per antenna are provided and the GS that are not performing well can clearly be identified for further investigation.

The simulations produced a considerable wealth of technical data, amounting to thousands pages of simulation run results and available on SJU extranet for reference and detailed study.

The key findings of the study are that:

On the high density area, single frequency implementation is insufficient to service contemporary (2015) bandwidth demand. Progressive extension of VDL2 implementation to the four frequencies already allocated will alleviate the negative trend and postpone the bandwidth exhaustion horizon until 2025, or even later if a suitable network load balancing policy is implemented.

On the medium density area, single frequency implementation will support service demand for another few years but not beyond 2020. Multi-frequency implementation, utilizing dedicated channels per traffic type (Airport, TMA/En-route) as well as dual squitter solution now pioneered by ENAV will postpone the sunset date to at least 2030, perhaps more if a suitable network load balancing policy is implemented.

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1 ,QWURGXFWLRQ

1.1 Purpose of the document

In order to anticipate the evolution of the European datalink infrastructure, considering the expected ATS and AOC traffic growth from 2015 until 2040, this study identifies the time horizon by which VDL Mode 2 should reach its operational limits in Europe. Simulation scenarios considered the use of “one single frequency” as well as “up to four frequencies”.

The aim of this document is to summarize the results of the study and main findings. It provides clear evidences of the identified operational VDL Mode 2 limits, based on results coming from simulations.

1.2 Intended readership

The complete ATM community will be interested to check result of this study, so to better understand VDL Mode 2 limits and drive future investments.

Institutions can also identify well in advance which appears to be communication future needs for the European airspace, identifying perhaps which may be new technologies that may complement the VDL Mode 2 link and their required performances.

1.3 Inputs from other projects

This study has been done on such a way that is really not strictly related to any other study done in the past on this matter. Anyway, in order to identify the criteria that allowed us to determine VDL Mode 2 operational limits; we have used as reference some documents:

Link 2000+ DLS CRO Performance Monitoring Requirements, edition 1.3 – Eurocontrol

Requirements for monitoring through VDL Mode 2 channels edition, 0.4 - Eurocontrol

1.4 Acronyms and Terminology

Term Definition

ATM Air Traffic Management

ACARS Aircraft Communication Addressing and Reporting System

ACSP Air/Ground Communications Service Provider

AOC Aeronautical Operational Communications

APT Airport Domain

ATN aeronautical telecommunications network

ATS Air Traffic Services

CPDLC Controller-Pilot Datalink Communications

CSC Common Signalling Channel

DLS Data Link Service

ENR En-Route

FANS Future Air Navigation System

GS VDL Mode 2 Ground Station

i4D Initial 4D trajectory

LME Link Management Entity

MF Multi Frequency

OI Operational Improvements

PA Provider Abort

SESAR Single European Sky ATM Research Programme

SESAR Programme The programme which defines the Research and Development activities

and Projects for the SJU.

SF Single Frequency

SJU SESAR Joint Undertaking (Agency of the European Commission)

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Term Definition

Undertaking Agency.

TMA Terminal Area

TRTD Technical Round Trip Delay

USBG University of Salzburg

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2 &RQWH[WRIWKHVWXG\2EMHFWLYHV

Figure 1 - Existing and possible future communication systems aligned with SESAR deployment

Figure 1 depicts the SESAR communication infrastructure roadmap which is reflected in the European ATM master plan. This roadmap clearly shows the need to progressively transition from the existing infrastructure towards new datalink solutions. This transition is related to when the current (also called legacy) communication systems will become saturated and new communication systems need to be developed and deployed.

Therefore, it is important to identify when data link systems and especially VDL Mode 2 becomes saturated with respect to growing air traffic and new data based operations for ATM.

2.1 Objective of the study

The aim of this study is to match aircraft future ATS and AOC traffic requests with foreseen traffic growth, and so to determine when the VDL Mode 2 technology, on monofrequency or multifrequencies, will reach performances that are such to let the link considered as not usable for ATS purposes, that has more stringent requirement than AOC traffic.

Simulations provided an incredible amount of data that will be available as annex of this report. Other technical material will be uploaded on SJU extranet.

On the main body of this document, main results are summarized, with the help of graphs that give a clear understanding of when the study will foresee this VDL Mode 2 capacity limit.

The scope of the study address the capability of mono and multi-frequency VDL Mode 2 to support Datalink services across a number of scenarios. In particular, the analysis determines the capability (capacity and performance) of VDL Mode 2 to support the implementation of evolving datalink services within increasing traffic scenarios. It clearly demonstrated the point at which VDL Mode 2 will no longer be able to support the operational usage of ATS services foreseen within the SESAR Concept.

The results enable then the determination of the time horizon by when the introduction of more advanced datalink services will require greater datalink capacity & performance that VDL Mode 2 can offer. This addresses the evolution of traffic and datalink implementations.

Datalink services considered are:

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VDL Mode 2 Capacity and Performance Analysis • Airline Operational Communication (AOC) • ATN Baseline 2 (including initial 4D …)

The analysis addresses the time period 2015 through to 2040, with 5 year intervals.

The study is giving evidence of technical system loads/key parameters on typical aircraft, operating in dense continental airspace as well as a less busy continental airspace, in line with SJU call for tender requirements and KoM agreement. The following metrics are monitored (always minimum, maximum, average, 95 percentile, 99 percentile, standard deviation, sample count):

• Application Layer

o User Data Rate

o User Success Rate

o_{Application Delay}

o_{Application Loss / Drop Rate}

• Management Layer (VME)

o Logged on Aircraft

o Link Establishment Delay

o Hand Offs

o_{Broadcast Message Receivers}

• Data Link Services (DLS)

o_{Roundtrip Time} o AVLC Frames

• Medium Access Control (MAC)

o_{MAC Delay} o_{TM2 Occurences} o_{N2 Occurences} o T1 Occurences • Physical Layer o_{Channel Occupancy} o_{Offered Load} o_Throughput o Loss o Transmission Delay o_{Transmission Distance} o_{Signal Quality Parameter} o Collisions

o Cause of Failure

Taking account of services, link budgets, data volumes and timing, the predicted utilisation analysis clearly show how the evolution and take-up of services will drive utilisation and performance.

The analysis indicates clearly when VDL Mode 2 reaches its limitations, the consequence of reaching them and the assumptions being made.

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3 6LPXODWLRQVHWXS

Within this section we briefly describe the simulation methodology, assumptions and variants taken to assess the VDL Mode 2 capacity breakeven point – more detailed descriptions about the simulation modules and parameters used can be found in the annexes.

3.1 Methodology

During the introduction of new standards for data communication in aviation (i.e. mainly VDL mode 2, mode 3, and mode 4) a lot of research on the topic of VDL Mode 2 has been published; a paper called “characteristics and capacity of VDL Mode 2, 3, and 4 sub-networks” 1gave a good overview of the performance of each of those systems. Also, Eurocontrol conducted a study called “VDL Mode 2 Capacity Simulations” and published results in late 20062; USBG was part of this study.

Mobility Model .xml Topology Model

.txt .txt Ground-Station Information Topology Configuration Data VDL2 Protocol and Channel Simulator .xml VDL2 Report Generator .xml .xml

Seed 1 Seed 2 Seed n

Scenario Configuration Application Data Profiles .doc MS Word Report D 2.X .xml .xml .xml D 2.1 D 2. 2 D 2.X .doc

Input Data Final Report D3 .xls Air Traffic Growth Reports .xml .mdb Air Traffic in ECAC Area .txt .xls

Figure 2 - High Level view of simulation tool chain

1_{Steven C. Bretmersky, Robert R. Murawski, and Vijay K. Konangi. "Characteristics and Capacity of}

VDL Mode 2, 3, and 4 Subnetworks", Journal of Aerospace Computing, Information, and Communication, Vol. 2, No. 11 (2005), pp. 470-489.

2

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The approach of the VDL Mode 2 Capacity and Performance Analysis is based on a simulation tool chain where each element provides input to the next element of the chain. Each tool is based on a discrete event based simulation.

The first tool (NAVSIM3: Air Traffic Calculation) provides the mobility of aircraft of a complete day4 (i.e. 24 hours). The information of each aircraft is updated in discrete steps of 3 seconds5. Thereby, important aspects such as position (i.e. longitude, latitude, and altitude), vertical intent, current domain (i.e. APT, TMA, ENR, or ORP), and current sector information are provided. Aircraft are generated for the core area of Europe. The amount of aircraft is extrapolated to the desired scenario (i.e. year and growth scenario).

The second tool (VDL Mode 2 Topology Calculation) takes this information and calculates distances of individual aircraft to neighbouring aircraft and visible ground stations. The distances are updated in the same discrete steps as the granularity of the aircraft mobility model. Neighbouring aircraft are all aircraft which are within the radio horizon. The same is true for visible ground-stations. The second tool requires input data such as ground-station positions (latitude, longitude, and altitude), operating frequency, and parameters necessary for link budget calculation such as transmission power or antenna gain. Due to the geographical areas that have been assessed we did not consider any digital elevation model as obstacles are not expected within the evaluated area.

The third tool (VDL Mode 2 Protocol and Channel Simulation) takes the mobility, topology, data model, and additional scenario configuration parameters and produces VDL Mode 2 performance data. Each simulation scenario is simulated with multiple different initial seed settings, thus providing confidence intervals for all results. The gained performance data is stored for each seed in a separate xml file.

The fourth and final tool (VDL Mode 2 Report Generator) takes all performance data of a single scenario setup and calculates performance figures. These figures are then provided in separate simulation reports. These reports are auto-generated. For concluding comparisons the “VDL Mode 2 Report Generator” keeps data of interest for the final report.

3_{NAVSIM ATM/ATC/CNS Simulation Tool developed by Mobile Communications R&D (MCO) in}

close co-operation with University of Salzburg (USBG)

4

based on data provided by Eurocontrol/NM (former CFMU) for a reference day (whole ECAC area)

5_{might be simulated or derived (interpolated) from time steps of about 1 minute (e.g. Consolidated}

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3.2 Assumptions and variants

This subsection presents briefly the assumptions and variants taken to compile a representative set of scenarios. The following main simulation variants are taken into account:

• Air traffic growth

• Topology

• Network subscriber rate

• Simulation time period

• Equipage rate & data traffic

• Frequency deployment & management

• Alternative AOC communications means

3.2.1 Assumptions on air traffic growth

The air traffic reference (mobility) data has been provided on courtesy by Eurocontrol/NM. The following describes the main characteristics of the reference air traffic data:

Ͳ Reference Day: _{August 29}th_{, 2014 (last Friday in August; high/peak day of year 2014)}

Ͳ Type of Flights: _{All IFR Flights (within / to / from) ECAC area on reference day}

Ͳ Number of Flights: _{32.817 (within 24 hours)}

Figure 3 - Traffic Growth within ECAC Area

Main data provided for each flight:

Ͳ Callsign / Operator

Ͳ Type of Aircraft

Ͳ Departure and Destination Aerodrome

Ͳ ETD, CTD, ATD (Estimated, Calculated, Actual Time of Departure)

Ͳ ETA, CTA, ATA (Estimated, Calculated, Actual Time of Arrival)

Ͳ Flight Route by Point Coordinates (Latitude, Longitude and Altitude / FL)

Ͳ Flight Route by Air Space Profile (Entry / Exit Time)

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Figure 3 shows the expected number of flights within the whole ECAC area for the years 2014 to 2050; Scenarios A, C, and D) based on the reference day (August 29th) of year 2014. While scenario A is assumed to be optimistic, scenario C seems to be a realistic growth model for the coming years. Consequently, we decided to investigate those two scenarios.

Variants

Baseline Scenario: Year 2015

Air Traffic Growth Scenario A (years 2020, 2025, 2030, 2035 and 2040) Air Traffic Growth Scenario C (years 2020, 2025, 2030, 2035 and 2040)

3.2.2 Assumptions on topology

Figure 4 - European VDL Mode 2 GS topology and simulated reference area

Figure 4 gives an overview of the simulated reference area and the involved data link topology. The black lines indicate simulated air traffic tracks. The red ellipses show the areas of interest for a high data link usage environment (High density area) and a medium data link usage environment (Rome area), respectively. These areas are represented as ellipses as the Mercator projection distorts the circular area of interest with a radius of roughly 150 nautical miles. Each available VDL Mode 2 ground station within the simulated reference area is simulated, however, evaluated are only those which are located within the areas of interests for high and low data link usage, respectively. These ground station positions are represented as orange circles – the remaining ground stations are represented as green circles.

The areas of Lille and Rome have been selected to represent high and medium data link usage environments, respectively. The area with high air traffic density is the area with roughly 150 nautical miles (nm) radius around Lille, France. All major airports within the capital areas of London, Paris, Brussels and Amsterdam lay within this area. Figure 5 highlights the number of flights within selected

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areas of interest. This figure clearly shows that the High density area contains most flights across Europe while Rome reflects an area with comparably low air traffic.

Figure 5 - Number of flights within selected areas of interest

NOTE: Details on the link budget calculation is given in ANNEX B

Evaluated ground stations of SITA network in high data link usage environment:

Code City Airport Country OWNER FRQ Power

AMS7 Amsterdam Schiphol Netherlands SITA 136,975 20 W BRU7 Brussels National Belgium SITA 136,975 20 W CDG7 Paris CDG France SITA 136,975 20 W CDX Paris CDG France SITA 136,975 10 W DUS7 Düsseldorf Int’l Germany SITA 136,975 20 W LCY7 London City

Airport

UK SITA 136,975 20 W LGW7 London Gatwick UK SITA 136,975 5 W LHR7 London Heathrow UK SITA 136,975 20 W NWI7 Norwich Int’l UK SITA 136,975 20 W ORY7 Paris Paris

Orly France SITA 136,975 20 W PAR7 Paris No Airport France SITA 136,975 20 W PARU Paris No Airport France SITA 136,975 10 W

Table 1 - SITA Ground Stations

Evaluated ground stations of ARINC network in high data link usage environment:

AMS Amsterdam - Netherlands ARINC 136,975 20 W BRU Brussels - Belgium ARINC 136,975 20 W CDG Paris - France ARINC 136,975 20 W LGW London - UK ARINC 136,975 20 W LTN London - UK ARINC 136,975 20 W ORY Paris - France ARINC 136,975 20 W

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STN Paris - France ARINC 136,975 20 W

Table 2 - ARINC Ground Stations

NOTE: for all SITA and ARINC VDL Mode 2 ground station antennas a loss attenuation of -3dB is assumed.

Evaluated ground stations of SITA/ARINC network in low data link usage environment:

Ciampino - Italy ENAV 136,975 10 W Fiumicino ATCR-33S - Italy ENAV 136,975 10 W Fiumicino SMR-B - Italy ENAV 136,975 50 W Napoli - Italy ENAV 136,975 50 W

Table 3 - ENAV Ground Stations

NOTE: for all VDL Mode 2 ground station antennas in Italy a loss attenuation of -4.5 dB is assumed. NOTE: In Italy all ground stations are operated by ENAV and have been manufactured by Selex-ES. Those ground stations have adopted criteria named “Dual Squitter”: The MGS Multi-Squitter is able to manage traffic for all the supported services (ATS and AOC) and for all the aircraft connected regardless the ACSP they belong, on a single VDL Mode 2 radio channel. This will reduce concurrency/collisions and hidden terminals by factor of 2 (more or less). This is achieved thanks to the serialization of the uplinks (ATS, AOC ACSP1 and AOC ACSP2) over the same AVLC links, using a single radio and antenna. The MGS is configured to broadcast different GSIF in using the same VDL Mode 2 radio in order to reach and connect all the aircraft. The simulator has been setup in a way to consider this particular behaviour of ENAV antenna.

NOTE: The transmit power level of the VDL Mode 2 ground stations in Italy are either significantly higher (50 Watt for Fiumicino SMR-B and Napoli) compared to the transmit power level of maximum 20 Watt (for ARINC and SITA stations in the high traffic area (Lille)) or are at the low end (10 Watt for Ciampino).

Variants

No variants for the topology with respect to ground station positions and ground station transmission characteristics have been investigated.

3.2.3 Assumptions on network subscription rate

In Europe SITA and ARINC have different subscriber rates that have been considered in the following way, based on info received by SITA and with the assumptions that the difference between CSP subscriptions will evolve in the future.

2015 2020 2025 2030 2035 2040 SITA Subscribers 70 % 68 % 66 % 64 % 62 % 60 % ARINC Subscribers 30 % 32 % 34 % 36 % 38 % 40 %

Table 4 - Network subscription rate assumptions

Table 4 shows an expected slight shift of the market share of about 2% every 5 years up to the year 2040 with a share for SITA and ARINC of 60% and 40% respectively in year 2040. Due to the fact that we have not taken additional ARINC ground stations into account, the impact on the study is a further slight degradation of the VDL2 link performance for those stations. The VDL2 performance

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could be improved - especially for the multi-frequency scenarios - if additional ARINC VDL2 ground stations will be available in the future.

Variants

No variants for different subscriber rates of ARINC and SITA users have been investigated

3.2.4 Assumptions on simulation time period

Figure 6 shows the peak instantaneous aircraft count (PIAC) for the ECAC region based on data as described previously. The figure shows maximum aircraft counts for different time frames during the day. It shows that the time frame between 10:00Z and 12:00Z is the one with most aircraft and the one with least variance. Therefore, this time frame has been selected to evaluate the performance and capacity demands of VDL Mode 2.

Figure 6 - Peak instantaneous aircraft count (PIAC) for the ECAC region

Variants

No variants for the evaluation time frame have been investigated.

3.2.5 Assumptions on aircraft equipage rate

The aircraft equipage rate reflects the relative amount of aircraft that are equipped with VDL Mode 2 transceivers. This does not mean that these aircraft are actively using the VDL Mode 2 equipment as communication means.

Year 2015 2020 2025 2030 2035 2040 2025 2030 2035 2040

VDL Mode 2 EQ

80 % 100 % 100 % 100 % 100 % 100 % 100 % 100 % 100 % 100 %

Table 5 - Aircraft equipage rate assumptions

Variants

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3.2.6 Assumptions on frequency management

Because there is not a standard yet on how to use the 4 frequencies assigned to VDL Mode 2 datalink, the consortium have elaborated options that came from a consultation of experts, as well as workshops done in Eurocontrol. The idea to use the frequencies “shared”, means based on domains, appears to be the most optimized way to use such frequencies.

So, in order to address multi frequency options 4 different possibilities are assumed (together with the option of the single frequency):

Channel Data traffic carried by frequency

FRQ Option16 FRQ 1

Ͳ Common Signalling Channel (CSC) data

Ͳ Data traffic of aircraft that stay in the airport (APT) domain

Ͳ Data traffic of aircraft that are flying in the TMA/ENR domain

FRQ Option 27 FRQ 1

Ͳ Data traffic of aircraft that are flying in the TMA/ENR domain FRQ 2 Ͳ Data traffic of aircraft that stay in the airport (APT) domain

Ͳ

FRQ Option 38

FRQ 1

Ͳ Data traffic of aircraft that are flying in the TMA/ENR domain FRQ 2 Ͳ Data traffic of aircraft that stay in the airport (APT) domain FRQ 3 Ͳ Data traffic of aircraft that are flying in the TMA/ENR domain

FRQ Option 49

FRQ 1

Ͳ Data traffic of aircraft that are flying in the TMA/ENR domain FRQ 2 Ͳ Data traffic of aircraft that stay in the airport (APT) domain FRQ 3 Ͳ Data traffic of aircraft that are flying in the TMA/ENR domain FRQ 4 Ͳ Data traffic of aircraft that stay in the airport (APT) domain

FRQ Option 510

FRQ 1

Ͳ Data traffic of aircraft that are flying in the TMA/ENR domain FRQ 2 Ͳ Data traffic of aircraft that stay in the airport (APT) domain and

Ͳ Data traffic of aircraft that are flying in the TMA/ENR domain

Table 6 - Frequency management assumptions

The algorithm for Frequency Options 2 to 4 to select one of the (up to 4) VDL Mode 2 frequencies in the Multi-Frequency (MF) scenarios is implemented as follows:

6

marked as SF (Single Frequency) in the VDL Mode 2 results charts (Chapter 5)

7_{marked as FO2 (CSC/APT/TMA/ENR + APT frequency) in the VDL Mode 2 results charts (Chapter}

5)

8_{marked as FO3 (CSC/APT/TMA/ENR + APT + TMA/ENR frequencies) in results charts (Chapter 5)} 9

marked as FO4 (CSC/APT/TMA/ENR + APT + TMA/ENR + APT frequencies) in charts (Chapter 5)

10

marked as MF4 (CSC/APT/TMA/ENR + 3 APT/TMA/ENR frequencies) in results charts (Chapter 5). This option is purely theoretical and is based on observations that University of Salzburg have done during simulation runs.

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An airborne VDL Mode 2 station (aircraft) always logs into the VDL Mode 2 network via the Common Signalling Channel (CSC; 136.975 MHz) responding to the periodically transmitted Ground Station Information Frames (GSIF).

Then the VDL Mode 2 ground station decides on which frequency the further communication data exchange is carried out.

For all aircraft in the airport domain (APT) either the CSC or one of the APT frequencies is chosen. This selection is based on the lowest number of aircraft11 allocated to a specific ground station. In case that the airborne VDL Mode 2 station (aircraft) is within the TMA/Enroute domain during the initial establishment of the VDL Mode 2 connection via the Common Signalling Channel (CSC) - on request of the VDL Mode 2 ground station – the aircraft is either handed over to the VDL Mode 2 frequency foreseen to handle TMA/Enroute data traffic or stays on the CSC. As explained above, this decision is based on the current lowest number of aircraft allocated to the VDL Mode 2 ground stations in question.

In case that the domain in which an aircraft is already in (either airport (APT) domain or TMA/Enroute domain) changes, that is either from APT domain to TMA/Enroute domain (initial phase of a flight) or from TMA/Enroute domain to APT domain, the VDL Mode 2 ground station decides whether a handover has to be carried out as follows:

Current domain Next domain Current frequency Next frequency Remark

APT TMA/ENR CSC CSC or TMA/ENR

APT TMA/ENR APT CSC or TMA/ENR

TMA/ENR APT CSC CSC or APT APT could be one of two APT frequencies TMA/ENR APT TMA/ENR CSC or APT APT could be one

of two APT frequencies The decision which VDL Mode 2 frequency to choose (CSC, APT or TMA/ENR) again depends on the lowest number of aircraft currently allocated to the target (next) frequency.

Variants

SF Single Frequency – Frequency deployment option 1 FO2 – Frequency deployment option 2

FO3 – Frequency deployment option 3 FO4 – Frequency deployment option 4 MF4 – Frequency deployment option 5

3.2.6.1 VDL Mode 2 Multi-Frequency Selection with load balancing

In addition to the VDL Mode 2 Multi-Frequency allocation and selection strategy described above, it has also been considered whether a different VDL Mode 2 Multi-Frequency approach would show benefits:

This consideration is based on the following: if an aircraft starts from some departure aerodrome and is landing on some destination aerodrome it would carry out communications over VDL Mode 2 during each phase of the flight:

• Start phase: comms at departure gate, during taxiing and take-off

• TMA/Enroute phase: during climb phase (TMA), enroute and arrival phase (TMA)

11_{further investigations (outside the scope of this study) could use the lowest data traffic load (or}

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• Final phase: during final approach, landing, taxiing and comms at destination gate.

By applying any of the VDL Mode 2 Multi-Frequency allocation and selection strategies described above (Frequency Options FO2, FO3 and FO4), the following frequency handovers would12 occur, during the flight phases mentioned above:

• Frequency Options FO2:

Ͳ during start phase: possible transition from Common Signalling Channel (CSC) to APT frequency

Ͳ during transition from start phase to TMA/enroute phase: from APT frequency to CSC

Ͳ during transition from TMA/enroute phase to Final phase: from CSC to APT

• Frequency Options FO3 and FO4:

Ͳ during start phase: possible transition from Common Signalling Channel (CSC) to APT frequency

Ͳ during transition from start phase to TMA/enroute phase: from APT frequency to TMA/ENR frequency

Ͳ during transition from TMA/enroute phase to Final phase: from TMA/ENR frequency to APT frequency

Conclusions: for all frequency options FO2, FO3 and FO4 a maximum of 3 frequency hand-offs are likely and will often occur: CSC > APT > TMA/ENR (or CSC) > APT

Instead of using the VDL Mode 2 Multi-Frequency selection strategy described above the following Multi-Frequency hand-off strategy (= Frequency Option 5) could be applied:

One (instead of up to three) frequency transition (if any) only from the CSC to any other of the available VDL Mode 2 frequencies (based on random selection or load balancing) is carried out; a reasonable number of VDL Mode 2 frequencies (2,3,4 or more13) could be made available, e.g.:

• MF2: possible transition (if any) from CSC to the other available frequency;

• MF3: possible transition (if any) from CSC to one of the other two available frequencies;

• MF4: possible transition (if any) from CSC to one of the other three available frequencies.

In addition to the Frequency Options FO2, FO3 and FO4 described above, this Frequency Option 5 (=MF4) with "load balancing" have been simulated for the high traffic area (Lille) and the medium traffic area (Rome) and the promising results are presented and discussed in Chapter 5 of this study.

3.2.6.2 ATS datalink program equipage rate

Current air traffic control is based on voice exchanges between aircraft crew and air traffic controllers. In order to introduce data link communication for air traffic control purpose, aircraft and air traffic control centres need to be equipped in terms of hardware and software. Currently the vision is that data link will be introduced for air traffic control in 3 phases. These phases are realized through programs called “ATN B1”, “ATN B2”, and “ATN B3”.

Assumptions with respect to ATS datalink program:

• 100 % ground equipage rate. That is, if aircraft are capable to use ATN B 1/2/3 data link message exchanges, they is able to use it at any time.

• If aircraft are capable to use ATN B2 they will use only the defined set of message for ATN B2.

• If aircraft are capable to use ATN B3 they will use only the defined set of message for ATN B3.

12

Note: there is always a chance, that a frequency handover does not occur and the VDL Mode 2 airborne station stays on the Common Signalling Channel CSC.

13_{Note: Only 4 available VDL Mode 2 frequencies have been simulated; larger numbers of available}

VDL Mode 2 Capacity and Performance Analysis