Interference on the B-VHF Overlay System

Transcription

1 REPORT D-09 Interference on the B-VHF Overlay System PROJECT NUMBER: PROJECT ACRONYM: PROJECT TITLE: INSTRUMENT: THEMATIC PRIORITY: AST3-CT B-VHF BROADBAND VHF AERONAUTICAL COMMUNICATIONS SYSTEM BASED ON MC-CDMA SPECIFIC TARGETED RESEARCH PROJECT AERONAUTICS AND SPACE PROJECT START DATE: DURATION: 30 MONTHS PROJECT CO-ORDINATOR: FREQUENTIS GMBH (1) (FRQ) A PRINCIPAL CONTRACTORS: DEUTSCHES ZENTRUM FÜR LUFT UND RAUMFAHRT E.V. (2) (DLR) D NATIONAL AIR TRAFFIC SERVICES (EN ROUTE) PLC (3) (NERL) UK LUFTHANSA GERMAN AIRLINES (4) (LH) D BAE SYSTEMS (OPERATIONS) LTD (5) (BAES) UK SCIENTIFIC GENERICS LTD (6) (SGL) UK UNIVERSITEIT GENT (7) (UGent) B UNIVERSIDAD POLITECNICA DE MADRID (8) (UPM) E PARIS LODRON UNIVERSITAET SALZBURG (9) (UniSBG) A DEUTSCHE FLUGSICHERUNGS GMBH (10) (DFS) D UNIVERSIDAD DE LAS PALMAS DE GRAN CANARIA (11) (ULPGC) E DOCUMENT IDENTIFIER: D-09 REVISION: 1.1 DUE DATE: SUBMISSION DATE: LEAD CONTRACTOR: FREQUENTIS DISSEMINATION LEVEL: PU - PUBLIC DOCUMENT REF: 04A02 E Project funded by the European Community within the 6 th Framework Programme. ( )

2 History Chart Issue Date Changed Page (s) Cause of Change Implemented by DRAFT DC All sections New document Frequentis DRAFT DC 02 DRAFT DR 01 DRAFT DR 02 DRAFT DR 03 DRAFT DR 04 DRAFT DR Section 7 and Section 9 Updates from DLR and UniSBG Most sections Review comments provided by DLR Most sections Review comments from EC and FRQ Some changes in Sections 2,4,7, and Executive Summary and Section 7 Internal Review Update Section 8 Updates from UniSBG Most sections Consortium review Section 9 Further review comments provided by EC Frequentis Frequentis Frequentis UniSBG, Frequentis Frequentis Frequentis Frequentis DLR Authorisation No. Action Name Signature Date 1 Prepared Bernhard Haindl, Michael Schnell Approved Miodrag Sajatovic Dieses Dokument ist elektronisch freigegeben. This document is released electronically. 3 Released Christoph Rihacek The information in this document is subject to change without notice. All rights reserved. The document is proprietary of the B-VHF consortium members listed on the front page of this document. No copying or distributing, in any form or by any means, is allowed without the prior written agreement of the owner of the proprietary rights. Company or product names mentioned in this document may be trademarks or registered trademarks of their respective companies. Copyright B-VHF Consortium Page: I

3 Contents 1. Introduction Executive Summary Scope Structure of the VHF NAV Band Utilization in the band MHz Band MHz Band MHz Instrument Landing System Frequency assignment planning criteria for ILS Characteristics and basics of ILS Localizer Signal VHF Omni-directional Range Navigation System Characteristics and basics of VOR signals Ground-based Augmentation System Impact of B-VHF transmission on aircraft navigation systems Structure of the VHF COM Band Usage of VHF Frequencies VHF Frequency Planning Criteria Services and frequency protection volumes Aerodrome Approach En route Other functions Characteristics of VHF Radios and Signals Characteristics of VHF Signals in Space Propagation of VHF Signals Propagation Models Copyright B-VHF Consortium Page: II

4 Free Space Propagation Model Aeronautical Standard Propagation Model Doppler Specifications Offset-carrier Operation B-VHF Interference Modelling Scope of Interference Scenarios Narrowband Interference Modelling Interference Classification Characterization of Interference Signals Threshold P Threshold Air Traffic / ATC & CNS Simulation Tool (NAVSIM) COM and ATC Sector Data Bases Used as Input for NAVSIM Approach for VHF Channel Occupancy Evaluation Determination of ATC Sector B-VHF Interference Modelling with NAVSIM Link Budget Characteristics Observation Points for B-VHF Interference Modelling VHF Channel Occupancy / Interference Results and Statistics Comparison of VHF Channel Occupancy Calculations and Measurements Comparison of VHF Channel Occupancy Calculations with B-VHF Measurement Flights Comparison of Measured and Calculated Received Signal Power Example Discussion and Verification of Measured and Calculated Received Power Statistics of Comparison between Calculations and Measurements Conclusions for Validation Assessment of B-VHF System Performance using NAVSIM B-VHF Capacity Analysis Results from Worst-case Simulations with NAVSIM B-VHF System Design with Respect to Interference Avoidance Towards Legacy Systems Estimation of Available B-VHF System Capacity Copyright B-VHF Consortium Page: III

5 9.4. Measures for B-VHF Capacity Improvement Summary and Conclusions References Abbreviations Appendix A Link Budget Analysis System parameter description Required carrier power-to-noise ratio Link budget calculation Transmission Power Sector Size Assumed System Parameters: Copyright B-VHF Consortium Page: IV

6 Illustrations Figure 1-1: B-VHF Project Work Breakdown Structure Overview Figure 4-1: Horizontal Antenna diagram of an ILS localizer Figure 6-1: Radio Horizon Sketch Figure 7-1: Interference basic chain Figure 8-1: VHF Channel Occupancy Calculation for Brussels/National Airport (1) Figure 8-2: VHF Channel Occupancy Calculation for Brussels/National Airport (2) Figure 8-3: VHF Channel Occupancy Calculation for Brussels/National Airport (3) Figure 8-4: VHF Channel Occupancy Calculation for Brussels/National Airport (4) Figure 8-5: VHF Channel Occupancy Calculation for Brussels/National Airport (5) Figure 8-6: VHF Channel Occupancy Calculation for Brussels/National Airport (6) Figure 8-7: B-VHF Flight from Southend to Bornemouth on Sep. 1, Figure 8-8: Comparison of calculated VHF Channel Occupancy and measured Results Figure 8-9: Comparison of calculated and measured received power (1) Figure 8-10: Comparison of calculated and measured received power (2) Figure 8-11: Comparison of calculated and measured received power (3) Figure 8-12: Comparison of calculated and measured received power (4) Figure 8-13: Comparison of calculated and measured received power (5) Figure 8-14: Comparison of calculated and measured received power (6) Figure 8-15: Comparison of calculated and measured received power (7) Figure 8-16: B-VHF Flight from Tees-Side to Southend, on July 8, 2004, 16:12; feet Figure 9-1: Calculation of the maximum allowed B-VHF transmission power and the resulting SIR at a B-VHF receiver for a B-VHF cell radius of 20 nm and an interference power threshold of -75 dbm Figure 12-1: BER as a function of Eb/N Figure 12-2: BER vs Eb/N0 for QPSK Modulation with different coding rates Copyright B-VHF Consortium Page: V

7 Tables Table 4-1: Table of required separation distances [CEPT ARC] Table 4-2: Table of required D/U signal ratios for GBAS [CEPT ARC] Table 4-3: Required D/U signal ratios for GBAS to VOR and vice versa [CEPT ARC]. 4-5 Table 5-1: ICAO EUR VHF Frequency Allocation Table 6-1: Parameters of Ground and Airborne VHF Transmitters and Receivers Table 6-2: Signal-in-space Characteristics of VHF Signals Table 6-3: Doppler Specifications for Aeronautical Communications Systems Table 6-4: ICAO Proposed Offsets and Stability for 25 khz CLIMAX Operation Table 7-1: Scope of Interference Scenarios Table 8-1: VHF Station Link Budget Parameters used in NAVSIM Table 8-2: Table 9-1: Table 9-2: Table 9-3: Table 9-4: Table 9-5: Median of Measured and Calculated Received Power of ATIS and Airport VHF Stations EIRP levels of the different transmitter types as used in NAVSIM simulations Results from the worst-case simulations with NAVSIM for B-VHF cells with different cell size evaluated at different flight levels at Munich airport Results from the worst-case simulations with NAVSIM for B-VHF cells with different cell size evaluated at different flight levels at Brussels airport Results from the 1 st measurement flight performed on different orbits, i.e., flight level and radius, within Bovingdon VOR, UK Maximum allowed B-VHF transmit power (aircraft and ground station) as well as resulting SNR and SIR at the B-VHF aircraft for different scenarios at Munich airport Table 12-1: Forward/Reverse Link Power Budget for B-VHF en-route sector Table 12-2: Forward/Reverse Link Power Budget for B-VHF TMA sector Table 12-3: Forward/Reverse Link Power Budget for B-VHF airport sector Copyright B-VHF Consortium Page: VI

8 1. Introduction Air transport has been identified as a dominant factor for sustainable economic growth of the European Union. The "Vision 2020" clearly points out the cornerstones of a future air transport system and the Advisory Council for ATM Research in Europe (ACARE) elaborates these requirements in depth in their "Strategic Research Agenda". A/G communication is the key enabler for achieving an Air Transport System that is capable of meeting future demands. The communications in the VHF aeronautical communications (COM) band ( MHz) are particularly attractive as they provide adequate coverage with moderate equipment power and acceptable price. Today, an analogue VHF voice communications system is still used for tactical aircraft separation and guidance. This communications technology has been introduced in the '40s and generally utilises the available VHF spectrum in an inefficient and inflexible manner. A small part of the COM spectrum is used by several types of aeronautical data links (ACARS, VDL Mode 2, and VDL Mode 4) for safety-related data link communications. After 2010, the VHF COM band in Europe is expected to become progressively saturated. This is expected to happen in spite of the recent introduction of the 8.33 khz DSB-AM voice system and the VDL Mode 2 data link that both use the VHF spectrum in a more efficient manner than the "old" solutions. The main reason for the saturation is the traditional ATM operational concept based on the tactical control of aircraft that generates increased demand for voice communications channels proportional to the increase in air traffic itself. The problem can only be solved by adopting new ATM concepts. Strategic European documents and recent studies indicate that a relief after 2010 may be achievable with intensive usage of the aeronautical data link. The tactical Air Traffic Control (ATC) will shift towards strategic Air Traffic Management (ATM), and at the same time the demand for new VHF voice communications channels would be reduced. Today s VHF solutions including VDL Mode 2 data link - cannot fulfil performance and capacity requirements of future data link applications. As there are no plans to deploy VDL Mode 3 system in Europe, VDL Mode 4 remains as only European option to replace VDL Mode 2 data link in the future. VDL Mode 4 as a pure data link technology without support for voice communications is capable to solve only a part of the congestion problem. In order to provide expected data link capacity, VDL Mode 4 would require multiple VHF channels that are difficult to find and coordinate. As there are still some unresolved architectural issues, there is no guarantee that VDL Mode 4 airborne radio can be operated without interference with analogue VHF voice radios. EUROCONTROL s Communications Strategy clearly points out the need for alternative communications systems. Air Traffic Service Providers (ATSPs) prefer keep on using their existing ground communications facilities, so an integrated voice-data system in the VHF range would be highly appreciated, being capable of using same physical locations of ground stations and same interconnecting infrastructure as the current VHF system. Therefore, more and more attention in Europe is directed towards broadband VHF technologies. Within the course of the B-VHF project bottom up research on multi-carrier technology (MC) for aeronautical communications is carried out. This work will result in the definition of a new future MC broadband VHF (B-VHF) system, which is able to support Single Copyright B-VHF Consortium Page: 1-1

9 European Sky, Free Flight and other advanced concepts and programmes, leading far beyond 2015 into Vision The B-VHF project is conducted under Priority #4/ Aeronautics and Space of the Sixth Framework Programme (FP6) of the European Commission (EC). The target technology is MC-CDMA, a highly innovative, high capacity technology that is also discussed for fourth generation (4G) mobile communications systems. However, the project will investigate possible implementation outside the VHF range, as well as non- CDMA access schemes. The B-VHF system has the potential to exploit the mobile VHF aeronautical channel better than any currently discussed VHF communication alternative. It increases voice and data capacity and addresses security and safety issues, promising a service level that is today unknown to the aeronautics user. Moreover, it has the potential to preserve the excellent inherent cost-range characteristics of the VHF band. It may eventually be applied as an overlay system and co-exist with the available VHF infrastructure, providing smooth transition and rollout scenarios. The proposed B-VHF system will support both voice and data link communications. The main expected benefits of the future B-VHF communications system are:! High spectral efficiency - the broadband B-VHF system uses VHF spectral resources more efficiently than today's narrowband VHF communications systems! High communication capacity - the total capacity of the B-VHF system is higher than the aggregate capacity of VHF systems deployed today or planned for a near future! Flexibility - the B-VHF system may be easily adapted to provide support for new operational and communications requirements! Security - the B-VHF system is inherently resistant against narrowband jamming and provides mechanisms supporting end-to-end data security! Sound transition path - the B-VHF system uses the knowledge about the current usage of VHF spectrum and may be able to share the VHF spectrum with legacy narrowband VHF systems without adverse interfering effects The high-level goal of the B-VHF project - proving the feasibility of the broadband MC- CDMA technology and demonstrating its benefits to the aeronautical community - requires a series of interrelated tasks that have been encapsulated as five separate workpackages in the B-VHF project:! WP 0 "Project Management and Quality Assurance"! WP 1 "B-VHF System Aspects"! WP 2 "VHF Band Compatibility Aspects"! WP 3 "B-VHF Design and Evaluation"! WP 4 "B-VHF Testbed" Figure 1-1 summarises the detailed work breakdown of the B-VHF project, including main work packages and all sub-work packages: Copyright B-VHF Consortium Page: 1-2

10 WP 0 Project Management and Quality Assurance WP 1 B-VHF System Aspects WP 2 VHF Band Compatibility Aspects WP 3 B-VHF Design and Evaluation WP 4 B-VHF Testbed WP 0.1 Project Management WP 1.1 B-VHF Operational Concept WP 2.1 Theoretical VHF Band Compatibility Study WP 3.1 VHF Channel Modelling WP 4.1 Baseband Implementation WP 0.2 Validation and QM WP 1.2 Reference Environment WP 2.2 VHF Channel Occupancy Measur. WP 3.2 PHY Layer Design & SW Implementation WP 4.2 VHF Frontend Development WP 0.3 Knowledge Management WP 1.3 B-VHF Deployment Scenario WP 2.3 Interference Modelling WP 3.3 DLL Layer Design & SW Implementation WP 4.3 B-VHF Testbed Evaluation WP 3.4 Protocol Design & SW Implementation Project Management Research, technological development and innovation WP 3.5 B-VHF Evaluation Figure 1-1: B-VHF Project Work Breakdown Structure Overview WP 0 "Project Management and Quality Assurance" comprises all activities that are essential to all work packages. It takes care of achieving high quality results throughout the whole project. It covers all management activities on Consortium level, in particular the information exchange and co-ordination with the European Commission and with the partners. A separate sub-work package has been destined for the validation and quality control which reflects the importance of maintaining high quality outputs in all project phases. Another sub-work package is dedicated to manage new knowledge generated within the B-VHF project in terms of intellectual property rights and dissemination strategies. WP 1 "B-VHF System Aspects" establishes the necessary connection between the scope and goals of the B-VHF project and the high-level objectives of the EC, European and global aeronautical community. Starting at the very beginning of the B-VHF project, this work package will produce high-level requirements for the B-VHF system, describe the reference aeronautical environment and produce the B-VHF Operational Concept document. By the end of the B-VHF project, the WP 1 will produce the B-VHF Deployment Scenario document, describing technological, operational and institutional issues of the B-VHF initial deployment, transition and operational usage. Copyright B-VHF Consortium Page: 1-3

11 WP 2 "VHF Band Compatibility Aspects" assesses by theoretical (modelling) and practical (measurements) means probably the most critical aspect of the future B-VHF broadband channel: its capability to be installed and operated "in parallel" with legacy narrowband channels, sharing the same part of the VHF spectrum, but remaining robust against interference coming from such legacy narrowband VHF systems. The investigations will also address the conditions for interference-free operation of the B-VHF system towards legacy narrowband VHF systems. The Theoretical VHF Band Compatibility Study developed in the WP 2 will provide inputs to the WP 1 required for the development of the B-VHF Deployment Scenario. Together with the B-VHF Interference Model developed in the WP 2, the Theoretical VHF Band Compatibility Study will also be used as input for the B-VHF system design and evaluation (WP 3). WP 3 "B-VHF Design and Evaluation" covers B-VHF system design tasks, starting with developing the model of the broadband VHF channel, and proceeding with the development and implementation of the SW representing the physical (PHY) B-VHF layer, DLL layer, higher protocol layers and representative aeronautical applications. The design and implementation tasks will be augmented by the development of detailed evaluation plans and corresponding simulation scenarios. The B-VHF Evaluation Reports produced in the WP 3 will provide necessary feedback to the B-VHF Deployment Scenario task of the WP 1. The WP 3 will also produce as a deliverable a complete set of the B-VHF System Design and Specification documents. The prime objective of the B-VHF project - demonstrating the capabilities of the MC-CDMA technology - will be achieved within the scope of the WP 3 by using intensive and layered simulation trials. This task will start with investigating the capabilities and performance of the B-VHF physical layer and will proceed by adding/integrating the DLL and upper protocol layers, respectively. The "generic" B-VHF technology validation will be concluded by considering specific requirements coming from the aeronautical environment and applications. The WP 3 will develop and implement a SW set of representative communications applications and verifies by simulation means that the B-VHF system can support a mix of such applications under nearly-realistic loading, while fulfilling the Quality of Service (QoS) and other requirements of each particular application. WP 4 "B-VHF Testbed" covers the baseband implementation and evaluation of a first B-VHF testbed for both the forward- and the reverse-link. The implementation is carried out in DSP technology and is restricted to the physical layer, which is the most critical part of the B-VHF development. The B-VHF baseband implementation is interfaced to the low-power broadband VHF frontend, thus, enabling testbed evaluation not only in the baseband but also in the VHF band. Testbed evaluation in the baseband is performed using channel and interference models, which are also implemented in DSP technology. The VHF band evaluation is carried out in the laboratory using actual VHF systems as interference sources and victim receivers, respectively END OF SECTION Copyright B-VHF Consortium Page: 1-4

12 2. Executive Summary The B-VHF project develops and validates basic functional principles and architecture of completely new VHF communications air ground sub-network technology, capable to support both current aeronautical communications needs and estimated future demands. The project deliverable D9 addresses together with deliverables D10, and D11 the interference aspects upon an overlay system. While deliverable D10 and D11 describe the requirements resulting from the overlay concept and the operating issues relating to system coexistence, respectively, D9 is focused on description of the VHF signals in space for the purpose of modelling the interference between the B-VHF system and legacy narrowband systems. Additionally, it provides a theoretical determination of the expected received power in each narrowband VHF channel in a future B-VHF cell in order to get a first estimation of the available bandwidth. The approach for this detailed VHF channel occupancy evaluation was done by using an adapted version of the ATM/ATC & CNS simulation tool NAVSIM. This tool uses a database, which contains all relevant information of the European airspace in order to simulate worst case scenarios for a specific area around a defined reference point. The result of this occupancy evaluation is used as input for a first analysis about the available bandwidth that can be used for the B-VHF overlay system. This estimation together with the B-VHF robustness against narrowband interferer will primarily influence the decision on the used transition scenario. In addition, the «Interference on the B-VHF Overlay System» document (D9) provides the following information:! The utilization of the VHF NAV band and the signal characteristics of the ILS and VOR system, respectively.! Requirements for the B-VHF system caused by the VOR system in the adjacent NAV band.! Description of the VHF COM band and the usage of VHF frequency resources by the current VHF systems.! Characteristics of aeronautical VHF radio systems and signals in space, which are possible narrowband interferers for the B-VHF system, including the detailed transmission power, spectral mask and frequency assignment.! Brief description of the propagation models used for the worst case interference simulation.! Explanation of the approach used by ATC & CNS Simulation Tool NAVSIM for the VHF channel occupancy and interference modelling.! Description of the comparison between VHF Channel Occupancy Calculations and flight measurements. By this comparison the verification of NAVSIM Simulator has been carried out.! Determine the interference power levels in each of the 760 VHF channels of 25 khz bandwidth in the VHF band range from ,975 MHz within a specific geographical range.! First estimation of the available bandwidth within the VHF COM band and definition of upper limits and constrains for the B-VHF system design. Copyright B-VHF Consortium Page: 2-1

13 ! Link budget analysis of a B-VHF system for three specific scenarios and determination of the power density threshold value for potential interference from the B-VHF system to existing VHF systems and vice versa END OF SECTION Copyright B-VHF Consortium Page: 2-2

14 3. Scope The purpose of the project deliverable D9 «Interference on the B-VHF Overlay System» is to provide necessary information for the B-VHF system design, interference modelling, as well as for the development of the B-VHF Operational Concept (D7) and B-VHF Deployment Scenario (D27). Main goal is to determine in a theoretically approach the expected received power in each narrowband VHF channel and with that the number of available VHF channels for the B- VHF system. Other important goal is describing the VHF signals in space for the purpose of modelling the interference between the B-VHF system and legacy narrowband systems. The document is divided into following sections:! Section 1 provides an overview of the B-VHF project, its goals and position within European ATM research framework and provides a brief summary of the deliverable D9 itself.! Section 2 gives a short review of the essential statements and information covered by this document.! Section 3 (this section) presents the purpose and structure of the D9 deliverable.! Section 4 describes the structure of the NAV band.! Section 5 describes in detail the structure of the VHF COM band.! Section 6 characterises VHF Radios and Signals.! Section 7 provides additional information on the procedure how the Interference Simulation and Modelling have been performed.! Section 8 covers the description of the used Air Traffic / ATC & CNS Simulation Tool, called NAVSIM.! Section 9 gives a first estimate of the VHF bandwidth available for the B-VHF system.! Section 10 captures reference documents used for producing this deliverable D9.! Section 11 lists abbreviations used throughout this document.! Section 12 (Annex A) gives a detailed overview about the B-VHF Link Budget Analysis performed for three different scenarios END OF SECTION Copyright B-VHF Consortium Page: 3-1

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16 4. Structure of the VHF NAV Band This section describes the usage of the VHF NAV band from ( MHz). This spectrum is currently used by the following VHF navigation systems:! VHF Omni-directional Range Navigation System (VOR),! Instrument Landing System (ILS),and! Ground-based Augmentation System (GBAS). Although the B-VHF project is focused on the VHF COM band and at present (in this project) there is no intention to extend the proposed MC based system to the NAV band it was decided to describe the structure and signals of the services in the NAV band. The decision was made especially for the following reasons:! As VHF NAV Band is adjacent to the VHF COM Band the impact of a B-VHF transmission on VHF NAV services has to be analysed.! Setting the basis and checking the pre-requisites for a possible future extension of the B-VHF system to the NAV band. This would be an expansion of the present MHz A/G communications band to support the transition to, and future growth of, the next-generation VHF A/G communications system for air traffic services. Of course this is only a thought experiment in order to check this scenario in principle, without any intention to propose a rearrangement of the NAV band, It has to be noticed that within this project no interference tests were planned to verify an operational impact from the proposed B-VHF system onto any system in the Navigation band Utilization in the band MHz The assignment of the frequency band MHz shall be as follows: Band MHz! ILS Localizer! GBAS The operation of VHF Data Broadcast (VDB) is not part of the baseline equipment. However, as VDB (GBAS) is expected to be introduced in the future, this information is important. VDB is intended to be assigned in the upper VOR band. The GBAS system is planned to use a channel spacing of 25 khz. The frequency assignment planning criteria to ILS and VOR are described in Annex 10 Volume I, paragraphs 3.1 and Attachment C [ANNEX10].! VOR provided that " No harmful adjacent channel interference is caused to ILS " Only frequencies ending in even tenths or even tenths plus a twentieth of a megahertz are used. The band MHz is used by ILS Localizer, VOR and GBAS (a Global Navigation Satellite System (GNSS) element), on different channels and the ILS Glide Copyright B-VHF Consortium Page: 4-1

17 Path is using the band MHz. Within the band MHz, channels on odd multiples of 100 khz (108.10, ) are used for ILS. Normally channels spaced 100 khz are used, however, in congested areas also the intermediate channels (50 khz) may be used Band MHz VOR: For regional assignment planning, the frequencies for VOR facilities shall be selected in the following order:! Frequencies ending in odd tenths of a megahertz in the band MHz! Frequencies ending in even tenths of a megahertz in the band MHz! Frequencies ending in even tenths of a megahertz in the band MHz! Frequencies ending in 50 khz in the band MHz! Frequencies ending in even tenths plus a twentieth of a megahertz in the band MHz Instrument Landing System The operational service area of an ILS Localizer is defined in Annex 10 and often formed as a "key-hole" out to 25 nm. The ILS Glide Path has shorter range and the frequency is fixed in relation to the ILS Localizer. For the co-channel case, the wanted signal must be at least 20 db stronger than an unwanted signal. The distance from the edge of the service area of the wanted station to another ILS on the same frequency should be more than 80 nm. Another ILS on the first adjacent channel (50 khz) should not be closer than 5 nm Frequency assignment planning criteria for ILS! Frequencies for ILS facilities should be selected from the list at [ANNEX10], Volume I, in accordance with the regional agreement permitted under [ANNEX10], Volume V, ! The co-channel and adjacent channel geographical separations between ILS Localizers and between ILS Glide Path installations should be as specified in Annex 10, Volume I, Attachment C, 2.6 for ILS Localizers designed for 50 khz channel spacing and for ILS Glide Paths designed for 150 khz channel spacing.! The geographical separations between ILS and VOR installations where they share the same channel or operate on an adjacent frequency should conform to the criteria stated at [ANNEX10], Volume I, Attachment C, 3.5. Copyright B-VHF Consortium Page: 4-2

18 Equipment Frequency Separation Minimum separation between second facility and the service volume of the first facility (nm) Localizer Glide Path Co-Channel 50 khz Co-Channel 150 khz Table 4-1: Table of required separation distances [CEPT ARC] Characteristics and basics of ILS Localizer Signal The ILS system (localizer and glide slope facility) provides vertical and horizontal navigational (guidance) information during the approach to landing at an airport runway. The localizer facility and antenna are typically located feet beyond the stop end of the runway and provides a VHF signal. The localizer system is based on the evaluation of two coherent amplitude modulated tones, which are transmitted via an antenna array (shown in Figure 4-1). Figure 4-1: Horizontal Antenna diagram of an ILS localizer The ILS information is drawn from amplitude modulation index of two continuous tones at 90 and 150 Hz. The difference in depth of modulation (DDM) allows determining the deviation from the centre line VHF Omni-directional Range Navigation System The band MHz is used by ILS Localizer and VOR, on different channels, while the band MHz is used only by VOR. Within the band MHz, all channels on even multiples of 100 khz (108.20, ) are used for VOR. Normally channels spaced 100 khz are used, however, in congested areas also the intermediate channels (50 khz) may be used. The VOR channels in this sub-band are usually used for terminal VOR, with short range. Within the MHz portion of the band all channels (100 and 50 khz) are available for VOR services (see [ANNEX10]). The designated operational coverage of a VOR can vary from 25 nm to approximately 200 nm and the protected altitude up to between feet and feet. Any unwanted signal must be at least 20 db lower than the signal from the desired station. If sectorization of the coverage is used, the range is not equal in all directions. Copyright B-VHF Consortium Page: 4-3

19 Characteristics and basics of VOR signals A VOR transmits two 30 Hz modulations resulting in a relative electrical phase angle equal to the azimuth angle of the receiving aircraft. A cardioid field pattern is produced in the horizontal plane and rotates at 30 Hz. A non-directional (circular) 30 Hz pattern is also transmitted during the same time in all directions and is called the reference phase signal. The variable phase pattern changes phase in direct relationship to azimuth. The reference phase is frequency modulated while the variable phase is amplitude modulated. The receiver detects these two signals and computes the azimuth from the relative phase difference. The VOR Signal can be described in the time domain as: x VOR (t) = Uˆ c cos( ω mt +ϕ VOR ) + cosω pt + x ref (t) cosωct circular _ pattern identifier reference signal (4.1) where ω m = 2π 30Hz, ω p = 2π 1020Hz and ω c = 2π fc. In this time domain representation is assumed that the identifier can be considered as a time invariant signal. The reference signal is frequency modulated with a hub of ±480Hz. The phase reference signal x (t)is ref ( ) x = cos ω t +ηcosω t, ω = 2π 9.96KHz ref ref m ref (4.2) 4.4. Ground-based Augmentation System The GNSS ground-based augmentation system VHF data broadcast frequency band is 108 to MHz. The lowest assignable frequency is MHz and the highest assignable frequency is MHz channel spacing is 25 khz. This band is also used for ILS (below 112 MHz) and for VOR. GBAS VDB applies a time division multiple access (TDMA) technique with 8 time slots which are repeated every 0.5 seconds. The signal timing is synchronised with UTC. The GBAS precision approach coverage is defined relative to the runway. However, it is recommended to use an omni directional designated operational coverage with a range of 23 nm and up to a height of feet above threshold. The GBAS positioning service coverage is dependent upon the specific operations intended. Undesired signals from cochannel GBAS or VOR stations must be at least 26 db below the desired GBAS signal. Adjacent channels up to ±100 khz must be considered in the compatibility assessment.! The signal ratios between desired and undesired signals (D/U) to protect GBAS precision approach VDB in the presence of an other GBAS station are: Copyright B-VHF Consortium Page: 4-4

20 Frequency offset 0 khz (co-channel) 26 db ±25 khz (first adjacent channel) -18 db ±50 khz (second adjacent channel) -43 db ±75 khz (third adjacent channel) -45 db Minimum D/U ratio required Table 4-2: Table of required D/U signal ratios for GBAS [CEPT ARC]! The signal ratios between desired and undesired signals (D/U) to protect GBAS receivers in the presence of a VOR signal and VOR receivers in the presence of a GBAS signal are: Frequency offset 0 khz (co-channel) 26 db ±25 khz (first adjacent channel) 0 db ±50 khz (second adjacent channel) -34 db ±75 khz (third adjacent channel) -46 db ±100 khz (fourth adjacent channel) -65 db Minimum D/U ratio required Table 4-3: Required D/U signal ratios for GBAS to VOR and vice versa [CEPT ARC] 4.5. Impact of B-VHF transmission on aircraft navigation systems Under the premise that the B-VHF system using the VHF COM band, it is essential to investigate the influence of the B-VHF system on aircraft systems working at adjacent frequency bands. At the current project it is too early to determine this impact by simulation or measurement tests, since the B-VHF system design is still in progress and there are too much system parameters undefined. Nevertheless it is important to take the issue of coexistent usage of both systems into account. Thus the following approach is applied to define on a first step some very rough requirements, which should be considered at the System Design. More accurate simulation or measurement test should be done in a possible follow-up project. For the impact of B-VHF transmission on VHF aircraft navigation system it was drawn on existing test with VDL Mode 2 interference tests [AMCP/WGB11]. As VOR band is adjacent to the VHF band, the tests aim in [AMCP/WGB11] was to study the spectrum spreading over the adjacent band and its operational impact, during VDL2 transmissions. With the results of these tests and the definition of following requirements for B-VHF it could be guaranteed that there are no operational impacts on the existing VOR and ILS equipment. Requirements on the B-VHF system: 1. The transmission spectrum mask of a B-VHF transmitter should be below the mask of a VDL Mode 2 Transmitter. 2. The power density of a B-VHF system should be less than of a VDL Mode 2 system Copyright B-VHF Consortium Page: 4-5

21 3. The antenna separation between a B-VHF and an aircraft navigation system must be at least as high as between present VDL Mode 2 and navigation system END OF SECTION Copyright B-VHF Consortium Page: 4-6

22 5. Structure of the VHF COM Band This section describes the usage of VHF frequency resources (channels) by the current VHF communications systems: DSB-AM voice, ACARS, VDL2 and VDL4 data link systems Usage of VHF Frequencies [EUR_FM_man] defines the allocation of VHF frequencies in Table 5-1. Block Frequency Allotment (MHz) A inclusive World- wide utilisation International / national AMS Special applications or remarks for Europe and reserved for regional guard supplementary tower and approach services; and reserved for regional light aviation B Emergency frequency Guard band required 1 C D inclusive inclusive International / national aerodrome surface communications National AMS - E Auxiliary frequency SAR Guard band required 2 F inclusive National AMS - G 123,45 Air-to-air communications Only for flights over some remote and oceanic areas H I inclusive inclusive International/ national AMS - National AMS - - J K inclusive inclusive International/ national AMS reserved for operational control communications; and reserved for ACARS data link; reserved for operational control communications, but no new assignments to be made (FMG/5) International/ national AMS A/G data link communications and reserved for ACARS until 2003; reserved for VDL Mode 4 tests; reserved for VDL Mode 2 Table 5-1: ICAO EUR VHF Frequency Allocation 1 Channels , , , , , are not assignable 2 Channels and are not assignable, except for ATIS Copyright B-VHF Consortium Page: 5-1

23 Note: 8.33 khz channel spacing is not to be used for frequencies MHz inclusive ([ANNEX10], Volume V, Note 1 to paragraph ). Some sub-bands are reserved for special purposes.! From to MHz only ground-ground communication is allowed, typically for communications between the TWR and taxiing aircraft.! The bands to MHz and to MHz are used by airlines for OPC according to special rules. Prior to co-ordination advice should be sought from EUROCONTROL.! The top four channels ( MHz) are reserved for data link.! In several states, common frequencies are used for applications such as light aviation, gliding and ballooning activities, etc. The sub-band MHz has initially been proposed for the initial implementation of the 8.33 khz spacing in European upper space. The information (data base) about current European 8.33 khz allocations has been provided by the EUROCONTROL [EUROC_VHF]. This data base uses abbreviations from the [EUR_FM_man] VHF Frequency Planning Criteria The band MHz is allocated to the aeronautical mobile service. It is used mainly for air/ground voice communications and, to some extent, air/ground data communications. The frequency implementation at the particular radio site is subject to the careful frequency engineering: the frequency itself, as well as the associated radiated RF power, must be allocated in such a way that interference-free operation is guaranteed under normal conditions within so called protected service volumes. The frequency protection volume of a service is usually identical to the Designated Operational Coverage (DOC). It defines the airspace where the frequency assignment planning process provides protection from other assignments. The ICAO planning criteria presented in [EUR_FM_man] do not provide protection against interference phenomena which may occur if communication facilities are co-located (e.g. interference caused by intermodulation). It is therefore possible that a proposed frequency is not acceptable due to specific local conditions. Depending on the type of service, the protected range can be from 16 nm to 260 nm or defined by the border of a FIR or sector. The protected altitude can vary from feet up to feet. Basically, for the voice communications two criteria apply, one for the implementation of the same frequency f 0, another one for the implementation of the adjacent frequency f 0 ± f, where f corresponds to the applicable frequency raster (25 khz or 8.33 khz). Protection by distance separation has in the past been achieved by making sure that any other transmitter (ground or airborne) is below the radio horizon. Alternatively, a recently introduced change to [ANNEX10] allows the regional use of a desired to undesired signal ratio of 14 db, equivalent to a 5 to 1 distance ratio, if this separation distance is shorter than the distance to the radio horizon. Copyright B-VHF Consortium Page: 5-2

24 Dedicated frequencies for operational control (OPC) purposes should be assigned to those aircraft operators who are required to maintain a system of Operational Control under the provisions of Annex 6, Part I. The [ANNEX10] provisions for frequency protection should not apply to OPC frequencies used in the EUR region (instead, these frequencies shall be shared by different operators) Services and frequency protection volumes The designations and abbreviations for different types of services [EUR_FM_man] are indicated below: Aerodrome! TWR Aerodrome control service! AS Aerodrome surface communications! PAR Precision approach radar! AFIS Aerodrome flight information service Approach! APP Approach control service! ATIS Automatic terminal information service En route! FIS Flight information service! ACC Area control service Other functions! A/A Air-to-air! A/G Air-to-ground! EMERG Emergency! OPC Operational control! SAR Search and rescue! VOLMET Meteorological broadcast for aircraft in flight END OF SECTION Copyright B-VHF Consortium Page: 5-3

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26 6. Characteristics of VHF Radios and Signals This section provides information about the characteristics of aeronautical VHF radio systems and signals in space. It comprises both voice and data link radio sub-systems of the VHF communications system Characteristics of VHF Signals in Space The reference [AMCP8-WP51] provides information about different narrowband VHF systems - DSB-AM, VDL2, VDL3 and VDL4 - for the purpose of developing frequency planning criteria in the aeronautical VHF band. Table 1 of [AMCP8-WP51] summarises parameters of air- and ground radio transmitters and receivers as used for purposes of interference assessment between airborne and ground radio equipment. The document [AMCP8-WP51] states, that the values for the radio frequency signal in Table 1 are to be used in the testing of equipment and the development of separation criteria for VDL. However, the proposed value for the ground DSB-AM transmitter power (100W) and the calculated EIRP value (80W) may be too pessimistic, as the calculated interference would always be very high, while the ground equipment with such high power may only be found at some specific locations outside UK. Note: Typical state-of-the-art en-route and TMA transmitters are specified for 50 W operation, whilst airport transmitters typically operate with 10W RF power. Additionally, not the TX declared power, but the EIRP radiated from the TX antenna is relevant for the B-VHF interference calculation. EIRP in turn additionally depends on the antenna gain (typical value is 2,15 dbi) and the (variable) feeder losses. The comparison of [AMCP8-WP51] values with practical representative values (UK) shows that 50 W of TX power combined with 3 db feeder loss could produce a more realistic EIRP value for the en-route and TMA ground systems. NOTE: Even if some equipment may be in operation in Europe with carrier power exceeding 50W, the EIRP at such locations may be the same as for 50W TXs, as the coverage requirements are comparable and the increased transmitter power mainly covers increased antenna feeder losses. For the purposes of the B-VHF project, original values from the [AMCP8-WP51] Table 1 for the transmitter power and EIRP have been corrected in Table 6-1 as follows:! En-route TX Power = 50W EIRP = 46 dbm! TMA TX Power = 50 W EIRP = 46 dbm! Airport TX Power = 10 W EIRP = 39 dbm As the interference modelling in the B-VHF project should be aligned with other aeronautical activities, it is proposed to use the values from Table 6-1 already including above corrections as representative for airborne and ground radios. NOTE: Table 6-1 also contains data about the VDL Mode 3 radios, however these are outside scope of the B-VHF project (as it is not very likely that VDL Mode 3 would Copyright B-VHF Consortium Page: 6-1

27 be implemented in Europe and the functional scope of B-VHF project extends the functional scope of the VDL Mode 3). NOTE: In the [AMCP8-WP51] feeder losses have (incorrectly) been given as negative values. This has been corrected in Table 6-1. Supplementary information about the characteristics of different VHF signals is given in Table 6-2, together with the references (in square brackets). Copyright B-VHF Consortium Page: 6-2

28 Parameter DSB-AM DSB-AM VDL-M2 VDL-M2 VDL-M3 VDL-M3 VDL-M4 VDL-M4 TRANSMITTER Airborne Ground 3 ) Airborne Ground Airborne Ground Airborne Ground Output power transmitter 44 dbm (25 W) 47/47/40 dbm (50/50/10 W) 42 dbm (16 W) 44 dbm (25 W) 44 dbm (25 W) 44 dbm (25 W) 43 dbm (20 W) 45 dbm (32 W) Feeder loss (assumed) 3 db 3 db 3 db 3 db 3 db 3 db 3 db 3 db Antenna gain (assumed) 0 db 2 db 0 db 2 db 0 db 2 db 0 db 2 db EIRP 41 dbm (12.5 W) 46/46/39 dbm (40/40/8 W) 39 dbm (8W) 43 dbm (20 W) 41 dbm (12.5 W) 43 dbm (20 W) 40 dbm (10 W) 44 dbm (25 W) Adjacent channel emission (Transmitter) 1 st adj ch. (16 khz bandwidth) -18 dbm -18 dbm -18 dbm -18 dbm -18 dbm -18 dbm 2 nd adj ch. (25 khz bandwidth) -28 dbm -28 dbm -28 dbm -28 dbm -28 dbm -28 dbm 4 th adj ch. (25 khz bandwidth) -38 dbm -38 dbm -38 dbm -38 dbm -38 dbm -38 dbm 8 th adj ch. (25 khz bandwidth) -43 dbm -43 dbm -43 dbm -43 dbm -43 dbm -43 dbm 16 th adj ch. (25 khz bandwidth) -48 dbm -48 dbm -48 dbm -48 dbm -48 dbm -48 dbm 32 nd adj ch. (25 khz bandwidth) -53 dbm -53 dbm -53 dbm -53 dbm -53 dbm -53 dbm RECEIVER Min signal at receiver antenna Annex 10, Vol. III 75 µv/m (-82 db m ) part II µv/m (-93 dbm) part II µv/m (-82 dbm) part I µv/m (-93 dbm) part I µv/m (-82 dbm) part I µv/m (-93 dbm) part I µv/m (-88 dbm) part I µv/m (-88 dbm) part I Feeder loss 3 db 3 db 3 db 3 db 3 db 3 db 3 db 3 db Antenna gain 0 db 2 db 0 db 2 db 0 db 2 db 0 db 2 db Min. signal at receiver input -85 dbm -94 dbm -85 dbm -94 dbm -85 dbm -94 dbm -91 dbm -89 dbm 3 Separate TX power and EIRP values proposed for En-route/TMA/Airport environment Copyright B-VHF Consortium Page: 6-3

29 Out-of-band immunity performance of receiver as per Annex 10, Volume III, Part I, paragraph (VDL) and Volume III, Part II, paragraph (DSB- AM). 1 st adj. Ch -40 db -40 db -40 db -40 db -40 db -40 db 4 th adj. Ch -50 db -50 db -60 db -60 db -60 db -60 db -60 db -60 db Table 6-1: Parameters of Ground and Airborne VHF Transmitters and Receivers Signal-in-space Type DSB-AM (25 khz) DSB-AM (8.33 khz) ACARS VDL-M2 VDL-M4 Modulation type A3E (double sideband AM with full carrier) A3E (double sideband AM with full carrier) A3E/MSK (13K0A2D, DSB-AM with in-band MSK modulation) D8PSK; see [RTCA-DO224A] Pulse shaping filter Raised cosine, α = 0,6; see [RTCA-DO224A] Modulation index 0,85; see [SPG/CP0108] 0,85; see [SPG/CP0108] 0,85; see [ARINC_618] Modulating signal type voice voice MSK; see [ARINC_618] Modulating signal frequency 0,3 2,7 khz; see [SPG/CP0108] 0,3 2,5 khz; see [DO-186A] 1200/2400 Hz tones; see [ARINC_618] Bit rate (kb/s) - - 2,4; see [ARINC_618] Burst duration 0 23 sec; see [VOCALISE_2] 0 23 sec; see [VOCALISE_2] 0,8 1,6 sec; see [WGB16/WP19] digital 31,5; see [RTCA-DO224A] 0,01 0,12 sec; see [WGB16/WP19] GFSK; see [ETSI_VDL4] Gaussian, BT = 0,28; see [ETSI_VDL4] - 0,25; see [ETSI_VDL4] digital ,2; see [ETSI_VDL4] 12 4 msec (see [DFS_VDL4]) 1 sec; see [ETSI_VDL4] 4 In [ETSI VDL2], the 1.3 % duty cycle has been proposed for single-slot messages (one Sync burst transmission in one slot every second). This value leads to the RF burst duration of 12 ms for single-slot broadcast messages. Such a burst would be followed by 988 ms of off status. In case of two-slot messages, the duty-cycle would be defined as 12 ms active status, followed by 1,25 ms off, then again 12 ms and finally 974,5 ms off. Maximum value of 1 s for the VDL4 physical burst has been specified bearing in mind long ATN frames and is not applicable to broadcast scenarios. Copyright B-VHF Consortium Page: 6-4

30 Signal-in-space Type DSB-AM (25 khz) DSB-AM (8.33 khz) ACARS VDL-M2 VDL-M4 Average burst duration Transmitter spectral mask (Attenuation from the unmodulated carrier level in dbc versus frequency offset from carrier in khz) TX frequency stability GND TX TX frequency stability - AIR TX 3,3 sec; see [VOCALISE_2] ±20 ppm; see [SPG/CP0108] ±30 ppm; see [DO-186A] 3,3 sec; see [VOCALISE_2] - 0 dbc between 0 2,5 khz; linear reduction from 0 dbc & 2,5 khz to 45 dbc & 3,2 khz; -45 dbc between 3,2 5 khz; -60 dbc above 5 khz; see [DO-186A] ±1 ppm; see [SPG/CP0108] ±5 ppm; see [DO-186A] ±20 ppm; see [SPG/CP0108] ±30 ppm; see [DO-186A] See Table 6-1 See Table 6-1 ±2 ppm; see [ETSI VDL2] and [SPG/CP0108] ±5 ppm; see [VDL2_AIR] ±2 ppm; see [ETSI_VDL4] ±5 ppm; see [VDL4_AIR] Table 6-2: Signal-in-space Characteristics of VHF Signals Copyright B-VHF Consortium Page: 6-5

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32 6.2. Propagation of VHF Signals Propagation Models Free Space Propagation Model The propagation loss for line of sight (LOS) wave propagation is defined by 4 π d L bf = log λ where: L bf : free space transmission loss, d: distance (m), and λ: wavelength (m) 20 (6.1) Equation (1) can also be written using the frequency instead of the wavelength L bf = log f + 20 logd (6.2) where: f: frequency (MHz), and d: distance (nm) Aeronautical Standard Propagation Model Aeronautical standard propagation model (ASPM) is derived from the ITU-R Recommendation P.528. For distances up to the radio horizon, free space propagation is assumed. Beyond the radio horizon, a constant attenuation factor a, which depends on the frequency band under consideration, is used. The distance to the radio horizon can be calculated using the following formula. RH E ( h h ) d = 2 k R + Tx Rx (6.3) where: d RH : distance to the radio horizon, k: effective Earth radius factor, R E : Earth radius. The Earth radius is R E = 6360km and if the atmospheric conditions are assumed to be normal then effective Earth radius factor k = 4/3, h TX : height of transmitting antenna above Earth s surface, and h RX : height of receiving antenna above Earth s surface Copyright B-VHF Consortium Page: 6-7

33 T x h Tx d RH R x h Rx k R E Figure 6-1: Radio Horizon Sketch If heights h TX and h RX are expressed in feet (ft) and the distance d in nautical miles (nm), the earth radius R E = 6360 km and if the atmospheric conditions are assumed to be normal (effective earth radius factor k = 4/3) the following practical formula can be used: ( ) d = 1,23 h + h (6.4) RH Tx Rx The propagation loss between two isotropic antennas, in a perfectly dielectric, homogeneous, isotropic and unlimited environment can be calculated as follows: L logd + 20 log f if d d RH bf ( d) = (6.5) a( d drh ) + L( drh ) if d > drh where: L bf (d): transmission loss between transmitter and receiver as a function of distance (db), d: distance between transmitter and receiver (nm), d RH : distance to the radio horizon (nm), f: frequency (MHz), and a: constant attenuation factor beyond radio horizon (db/nm). In the band MHz the variable a equals to 0.5dB/nm Doppler Specifications Relative velocities from 0 to 1200 knots between transmitter and receiver must be accommodated. The corresponding Doppler shifts will range between zero and ± 243/282 Hz at 118/137 MHz, respectively, with Doppler shift being proportional to the carrier frequency. The corresponding Doppler rates are 0 to 7,8 Hz/s for a 2g aircraft turn at frequency of 137 MHz, with Doppler rate being proportional to the acceleration. Copyright B-VHF Consortium Page: 6-8

34 Table 6-3 gives some examples calculated for 137 MHz. Aircraft velocity (mph) Aircraft height over GS (feet) Max. Doppler offset (Hz) ,2 17, Max. Doppler rate (Hz/s) Table 6-3: Doppler Specifications for Aeronautical Communications Systems Offset-carrier Operation [CLIMAX_TECH] summarizes ICAO recommendations on frequency offsets and provides information on required TX stability for CLIMAX operation on 25 khz channels: No. Of Climax legs Leg 1 frequency Leg 2 frequency Leg 3 frequency Leg 4 frequency Leg 5 frequency Stability 2 fc + 5 khz fc 5 khz ± 2 khz 3 fc khz fc fc 7.3 khz ± 0.65 khz 4 fc khz fc khz fc 2.5 khz fc 7.5 khz ± 0.5 khz 5 fc + 8 khz fc + 4 khz fc fc 4 khz fc 8 khz ± 40 Hz Table 6-4: ICAO Proposed Offsets and Stability for 25 khz CLIMAX Operation END OF SECTION Copyright B-VHF Consortium Page: 6-9

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36 7. B-VHF Interference Modelling In this section a first narrowband B-VHF Interference model is elaborated. This model is only used for the B-VHF bandwidth evaluation and therefore only reduced functionality is required, in comparison to interference models used for simulating transmission on the physical layer. A more detailed description about the interference model will be found in B-VHF project deliverable D14 «Software Implementation of the Interference Model». ([B-VHF D14]). Additional a classification of the interferer and a description of the used interference scenarios are given Scope of Interference Scenarios If a new system is phased in by an overlay concept then the following interference scenarios could be identified: Nb Scenario Comments 1 N to B_A 5 An airborne B-VHF receiver at the frequency range f B is jammed by the sum of airborne and ground narrowband transmitters (Inter-system interference). 2 N to B_G A ground B-VHF receiver at the frequency range f B is jammed by the sum of airborne and ground narrowband transmitters (Inter-system interference). 3 B to N_A An airborne narrowband receiver operating on the sector frequency is jammed by the sum of airborne and ground B-VHF transmitters (Inter-system interference). 4 B to N_G A ground narrowband receiver operating on the sector frequency is jammed by the sum of airborne and ground B-VHF transmitters (Inter-system interference). 5 B to B_G A ground B-VHF receiver at the frequency range f B is jammed by other airborne and ground B-VHF transmitters operating at the same frequency band (Co-Channel and Multi Access Interference). 6 B to B_A An airborne B-VHF receiver at the frequency range f B is jammed by other airborne and ground B-VHF transmitters operating at the same frequency band (Co-Channel and Multi Access Interference). Table 7-1: Scope of Interference Scenarios For evaluation of the available bandwidth for the B-VHF system only worst case simulations of scenario 3 and 4 of Table 8-1 should be taken into account. These scenarios characterize the impact of the B-VHF system on the existing systems in the VHF COM band. Since there are no B-VHF transmitters available the simulations in Section 8 were implemented with the current VHF DSB-AM system. This is possible because the propagation conditions in the aeronautical channel allow for predicting the received power for any given location in a simple manner, and therefore a simple link budget analysis is used to evaluate the interference power at a victim receiver. 5 The abbreviation N terms narrowband system and B terms B-VHF system, respectively. The subscription A and G is the abbreviation for ground and airborne, respectively. Copyright B-VHF Consortium Page: 7-1

37 Based on these worst-case simulations, the actual received interference power of scenario 3 or 4 can be calculated by replacing the DSB-AM system parameters with B- VHF system parameters Narrowband Interference Modelling A general interference model is typically based on the following scheme: Figure 7-1: Interference basic chain In Figure 7-1 above, the three different signals shown are the transmitted. The transmitted signal is represented with power P S, the added noise with power P N, and the interference itself, with a power P I. The signal i(t), corresponding to the interference, is calculated as follows, 760 k= 1 () jk ( 1) 0 ω t k k f i(t) = α i t e, 0 t T The different terms present in the last equation correspond to:! α k : estimated power in the corresponding channel.! ω 0 : narrowband channelization. This value should be 25 KHz, but is an input parameter to the Simulator.! i k (t): baseband interference over the k-channel. This signal is power normalized, T f 1 2 that is ik () t dt = 1. T f 0! ( k 1) ω t : frequency shifting to the corresponding channel, where 1, N ) j 0 e ( ch k.! T f : frame time interval. The received power of each "narrowband spectral line" (corresponding to the particular sector frequency), as seen by the victim receiver, will vary with time, dependent on which user at which distance is currently active on the channel. For the estimation of the available bandwidth for B-VHF system the interference chain in Figure 7-1 can be simplified. In this application an active transmitter for each channel is located at the worst case location (typically the nearest distance to the victim receiver). So the received power α k is dependent on the (calculated) LOS distance between the appropriate transmitter and the victim receiver. For each discrete narrowband jamming frequency a "time interference profile" (as seen by the victim receiver) could be constructed, consisting of the contributions of the particular worst case user. Copyright B-VHF Consortium Page: 7-2

38 7.3. Interference Classification Characterization of Interference Signals Since the B-VHF system is designed as an overlay system there must be some criteria to differ between available and reserved bandwidth. The anticipated operating concept for the B-VHF system is based on the a-priori knowledge about which VHF channels are active and operated within a given region. Due to the fact that the frequencies in the VHF COM band must be carefully planned, it is a-priori known, which ATC frequencies are locally used within a given geographical region. Dependent on this, some ground- or airborne stations can be considered as "strong/local" interferers, while the others belong to the "weak/ distant" category. Based upon the a-priori knowledge about "strong" interferers the local B-VHF system(s) would decide which of the ATC frequencies within the MC-CDMA frequency band are "available" at this particular location and which ones are not. The spectrum, which was nominally allocated to the weak narrow-band signals, would be re-used (overwritten) by the broadband MC-CDMA system, while the spectral areas occupied by the "strong" local signals would be selectively excluded. For this purpose two distinct types of interferers shall be defined within the B-VHF project (with respect to the maximum level of power they produce at the victim receiver):! Strong interferers (coming from the current and adjacent sectors), with a maximum possible power P > P Threshold! Weak interferers (coming from distant aircraft and ground stations), with a maximum possible power P < P Threshold The primary purpose of the threshold P Threshold is to allow determining which VHF channels are potentially available to the local B-VHF system and which are not. An aircraft or ground station at a distance corresponding to x > x Threshold cannot produce notable interference towards the B-VHF system. It the received interference power on such a frequency remains below P Threshold over the whole observation time T, such a channel would be available to the B-VHF system. Such a narrowband channel will not be disturbed in the opposite direction (assuming that the B-VHF transmitter power density received by the NB receiver within the NB bandwidth over given distance is lower than the power density the B-VHF receiver would receive from the NB transmitter over the same distance in the same bandwidth NB ). The B-VHF transmitter power will have to be adjusted to produce the minimum required SNIR at the B-VHF receiver input under total received interference power on all NB channels within the B-VHF bandwidth Threshold P Threshold The particular importance of identifying strong interferers is that the B-VHF system will have to consider such narrowband channels as close ones that require special treatment at the B-VHF transmitter and receiver that is not required for the weak interferers. Since the exact threshold is dependent on some B-VHF parameters (e.g. power density) and should be considered during system design, a range between -75 dbm to 85 dbm has been assumed in the simulations in Section END OF SECTION Copyright B-VHF Consortium Page: 7-3

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40 8. Air Traffic / ATC & CNS Simulation Tool (NAVSIM) One of the major tasks to support the B-VHF system design is to determine the available percentage of 25 khz channels in the VHF band (see Section 5 above), which can be used for the MC-CDMA overlay concept. In this section the modelling approach to determine the VHF channel occupancy of legacy VHF systems using an adapted version of the ATM/ATC & CNS simulation tool NAVSIM 6 is described. The results of the VHF occupancy evaluation based on NAVSIM simulations are important for a first B-VHF bandwidth analysis as outlined in Section 9 of this document COM and ATC Sector Data Bases Used as Input for NAVSIM In order to study the interference impact of legacy VHF systems on the B-VHF system and to carry out a detailed VHF channel occupancy evaluation the following input data are required:! Complete list of VHF radio stations / assigned VHF frequencies within the area of relevance 7 (Europe), including the following characteristics for each station: " Assigned VHF frequency (in the range to MHz) " Geographical position (in WGS84 co-ordinates) " Altitude " Transmit power, antenna gain and feeder loss " Type of station (Airport, TMA, En-route) " Supported service (e.g. TWR, APP, ACC, ATIS, VOLMET, OPC, etc.) " Assigned ATC sector.! Complete list of ATC sectors within the area of relevance (Europe), including the following characteristics for each ATC sector: " Borders of ATC sector (e.g. polygon or other structure, using WGS84 geographical co-ordinates as reference points) " Type of ATC sector (five different types are used: CTR, TMA, ACC low, ACC high, Other) " Assigned VHF frequency (in the range to MHz) " Upper altitude limit of ATC sector (e.g. FL 245) " Lower altitude limit of ATC sector (e.g. FL 100) 6 The Air Traffic / ATC & CNS Simulation Tool "NAVSIM" has been developed by "MCO Mobile Communications Research & Development Forschungsgesellschaft mbh, Salzburg" in co-operation with University of Salzburg. 7 Due to the fact that not only high dense areas like Brussels (EBBR), London Heathrow (EGLL) or Frankfurt (EDDF) are of interest for the B-VHF system design, but also areas with less dense air traffic (e.g. Munich (EDDM), etc.), NAVSIM has been adapted to allow VHF occupancy evaluation for any point in the three-dimensional airspace over Europe. Copyright B-VHF Consortium Page: 8-1

41 For the VHF channel occupancy and interference evaluations, data from various data bases ([NERL_GS], [EUROC_VHF] and data already available in NAVSIM, i.e. Swissair Flight Information System (SFS), Digital Aeronautical Flight Information and JEPPESEN NavData) are used in the NAVSIM tool:! NAVSIM Data (more than records): contain all the En-route and TMA/Airport frequencies, and all CTR, TMA, Approach, CTA/ATC Sectors, with lower and upper altitude / FL level, indicating the vertical airspace structure for which the specified ATC sector is valid; however it does not contain a direct mapping between the VHF frequencies and the ATC sector in which a specific VHF frequency is used. It specifies all ATC sectors accurately (e.g. also with arcs), which makes it however more complex for the ATC sector evaluation, as all airspaces had to be converted to corresponding polygons.! [EUROC_VHF] Data: contain all VHF frequencies and several ATC Sectors (mainly ACC sectors) for Europe. For a subset of VHF frequencies the corresponding ATC sector(s) (specified as polygons) is indicated. As a main drawback, the altitudes, for which a sector is valid in vertical direction is not indicated in the [EUROC_VHF] data base.! [NERL_GS] Data: contain accurate positions of radio stations; however there are several divergences between the [NERL_GS] data and the NAVSIM and [EUROC_VHF] data Approach for VHF Channel Occupancy Evaluation In this subsection it is explained how the NAVSIM tool has been adapted for the VHF channel occupancy and interference evaluations, taking the baseline data (described in 8.1 above) into account. In order to evaluate the VHF channel occupancy situation for a given airspace around a reference point in the three-dimensional airspace over Europe, the following stepwise approach is carried out:! Define a reference point (e.g. Brussels Airport (EBBR)) at a specific altitude (e.g feet (FL250)).! Define a range of interest around the reference point (eventually corresponding to a possible size of a B-VHF cell) by specifying a range ( 0 8, 20, 60, 100, 150, 200 nm around the reference point). Note, that for this area the VHF channel occupancy situation will be evaluated by placing a number of observation points within the area.! Place a victim receiver at the specified altitude at several observation points within the range of interest. Thus, a victim receiver with airborne VHF station characteristics (see Table 6-1) is placed either: " Directly at the reference point at the altitude corresponding to the GND level 8 In case of a range of 0, the area of interest is reduced to the single observation reference point, i.e. the position of the victim receiver corresponds to the reference point. Copyright B-VHF Consortium Page: 8-2

42 " At a specific altitude directly above the reference point, e.g feet (FL 050; see Figure 8-3 in Subsection 8.6 below), , , , , , and feet. " At a number of observation points at a certain altitude within the specified range of interest around the reference point. One point is placed directly above the reference point, 12 points are equally spaced (with a bearing of 0, 30, 60, 330 degrees, in 30 degree steps) on the perimeter of the circle with the radius of 20 nm, additional 12 points on the circle with radius 60 nm e.t.c. The largest circle carrying the last 12 observation points corresponds to the specified range of interest. When considering interference coming from the airspace above or below a range of interest, additional observation points are placed directly above each ground station found within a range of interest. Note: The altitude (in feet) of the victim receiver is indicated in the header of the VHF channel occupancy result graphics as depicted in Figure 8-1 to Figure 8-6 in Subsection 8.6 below. A stepwise approach is applied when calculating the VHF occupancy, separately for each VHF frequency and each observation point within a range of interest. Note: The radio horizon has been determined by assuming the Earth to be an ideal sphere, without taking terrain profile into account. Note: A free-space propagation model is used, as described in Subsection 6.2.1, taking EIRP, VHF frequency, distance, receiver antenna gain and feeder loss into account (see Table 6-1). For all VHF channels supporting ATC sectors/functions:! Check whether the VHF ground station (airport, TMA, en-route) involved with this VHF channel lies within the radio horizon as seen from the current observation point/victim receiver. For each VHF ground station which supports a specific ATC sector/function (e.g. Tees-side Tower, Southend Approach or London ACC), is lying within the radio horizon and is contained in the data base, calculate received signal power (dbm) at the input of the victim receiver placed at the current observation point, taking into account position/altitude of a victim receiver, position 9 and altitude of interfering GS, distance between the interferer and the victim receiver, EIRP of the interfering transmitter, dependent on the type of the transmitting station (as listed in Table 8-1), victim receiver antenna gain and feeder loss (see Table 6-1). Store the maximum calculated received signal power (across all GSs for a given VHF channel).! In each ATC sector put a representative interfering A/C at a worst case position (on the sector perimeter, at the highest possible altitude within this sector and at the closest possible lateral distance to the victim receiver). As for ground stations, only representative interfering A/C appearing within the radio horizon - as seen from the observation point/victim receiver - are considered. Representative interfering A/C in the sectors above/below the current observation point are placed at the closest possible vertical distance (directly above/below the current 9 For non-uk GSs, where the exact position of the VHF station is not available in the data base, the GS is assumed to be located in the centre of the footprint of the ATC sector it supports. Copyright B-VHF Consortium Page: 8-3

43 observation point). Calculate the received signal power (dbm) at the input of the victim receiver dependent on the type of the transmitting station by using the same set of parameters as used for calculating interference power produced by the GS. Store the calculated received signal power for a given 25 khz VHF channel.! Select the higher of above two values as a representative peak value for a given VHF channel at a given observation point.! Repeat the procedure for all other observation points within the range of interest and determine the overall maximum peak value as representative for this VHF channel. Note: One observation point is always put directly above each GS found within a range of interest, producing the worst-case with respect to interference coming from that GS.! Repeat for all other 25 khz VHF channels that are associated with ATC sectors/functions. For all VHF channels/ services other than ATC sectors/functions:! Check whether the VHF ground station involved with this VHF channel lies within the radio horizon as seen from the current observation point/victim receiver.! Calculate for all VHF ground stations contained in the data base, which support some particular service (e.g. ATIS, VOLMET, OPC) different than ATC sector/function the received signal power (dbm) at input of the victim receiver placed at the current observation point, taking the same factors into account as when considering interfering ground stations providing ATC sector/function services. Store the maximum calculated received signal power (across all GSs) as a representative peak value for a given VHF channel at a given observation point).! Repeat this procedure for all other observation points within the range of interest and determine the overall maximum peak value as representative for this VHF channel. Note: One observation point is always put directly above each GS found within a range of interest, producing the worst-case with respect to interference coming from that GS.! Repeat for all other 25 khz VHF channels that are associated with non-atc sectors/functions. After the procedure described above has been performed, for each of the kHz VHF channels the overall maximum received signal power is determined for each range, taking all ground- and airborne interference sources and all observation points into account. This is the relevant parameter, which is used for further VHF channel occupancy and availability calculations and statistics. The VHF station, for which the overall maximum received power has been calculated for a given VHF channel, is stored and characterised by the following information: " Name/ID of VHF station " Type of VHF station " Supported service of VHF station (e.g. ATIS) " Distance to victim receiver and distance to reference point Copyright B-VHF Consortium Page: 8-4

44 The occupancy for a given range is calculated by performing the following steps:! Specify a threshold value (in dbm) for further VHF channel occupancy calculations and statistics.! Determine the total number of VHF channels and corresponding percentage for which the obtained overall maximum peak value is above the specified threshold value. This is the number / percentage of VHF channels, which are considered as "occupied" ("not available") for the B-VHF system within the investigated area.! Determine the distribution of the number of consecutive (adjacent) VHF channels which are available for the B-VHF overlay concept. In the following Subsections 8.3 to 8.5 below, the determination of the ATC sector, interference modelling using the NAVSIM tool, and selection of observation points for interference modelling, are described in more details. The complete list of calculated VHF channel interference / occupancy statistics along with some examples of interference scenarios are described in Subsection 8.6 below. Note: The VHF Channel Occupancy evaluation approach described above models a worst case situation, due to the fact, that based on the assignment of a VHF frequency a 100% duty cycle is assumed for all VHF stations considered, which is not the case in the real world. However, for B-VHF system design, it is reasonable to follow such an approach, to make sure that interference from the B-VHF system towards the legacy VHF systems is eliminated or negligible. The expected interference from the legacy VHF systems towards the B-VHF system and vice-versa will be taken into account further in more details in the course of the B-VHF project Determination of ATC Sector In interference modelling, a victim receiver will be placed at selected 3D observation points, while the interferers will be either fixed VHF ground stations or airborne VHF stations placed at appropriate points around the victim. It is necessary to determine to which European ATC sector (airspace) a selected 3D point over Europe belongs to. The following approach is applied:! First, determine all ATC sectors (airspaces) that contain a footprint of the selected 3D point (2D point, defined by a geographic position: Latitude and Longitude in WGS84 coordinates), independently of the third co-ordinate (altitude).! Determine from this list the relevant ATC sector by applying a filtering algorithm, based upon: " ATC data base ([EUROC_VHF], NAVSIM, [NERL_GS]; in this order) " ATC sector type (CTA/ACC high, CTA/ACC low, TMA, CTR; in this order) " Lower and Upper limit (if specified) of each airspace " Altitude of the selected observation point (aircraft FL) The last item in the order mentioned above has the highest priority. With this algorithm it is possible to retrieve the relevant ATC sector. Copyright B-VHF Consortium Page: 8-5

45 8.4. B-VHF Interference Modelling with NAVSIM For VHF channel occupancy and interference evaluations, the following interference modelling approach has been taken into account, based upon assumed (realistic) parameters of ground and airborne VHF transmitters and receivers Link Budget Characteristics The link budget parameters (see Table 6-1), which are used in the NAVSIM simulations / calculations for VHF Ground Stations (Aerodrome, TMA, En-route) and VHF airborne stations are contained in Table 8-1 below. VHF Station Transmit Power Antenna Gain Feeder Loss Resulting EIRP Airport GS 40 dbm (10 W) 2 db 3 db 39 dbm (8 W) TMA GS 47 dbm (50 W) 2 db 3 db 46 dbm (40 W) En-route GS 47 dbm (50 W) 2 db 3 db 46 dbm (40 W) Airborne 44 dbm (25 W) 0 db 3 db 41 dbm (12.5 W) Table 8-1: VHF Station Link Budget Parameters used in NAVSIM For the victim receiver a feed loss of 3 db and an antenna gain of 0 db are assumed Observation Points for B-VHF Interference Modelling NAVSIM allows calculating VHF Channel Occupancy statistics in four different ways:! Victim receiver over fixed reference point 10 (e.g. Brussels (EBBR) or London Heathrow (EGLL)) at the following altitudes: " at airport elevation level " FL 050 (5.000 feet) to FL400 ( feet) in steps of (5.000 feet)! VHF Channel Occupancy simulation / calculation with regard to a specific geographical region around a reference point: " at airport elevation level, and " within ranges of 20 nm, 60 nm, 100 nm, 150 nm and 200 nm for the following altitudes: " FL 050 (5.000 feet) to FL400 ( feet) in steps of (5.000 feet)! Victim receiver on board of a simulated aircraft, for which any flight plan route in the European airspace can be specified, or! Victim receiver assumed to be on board of a B-VHF measurement flight for comparison / validation purposes between calculated VHF channel occupancy and VHF channel occupancy obtained from B-VHF flight measurements using a spectrum analyzer on board of the measurement aircraft (see B-VHF deliverable [B-VHF D12] for details). 10 In case that the victim receiver is fixed at a reference observation point, a range of 0 nm is indicated. Copyright B-VHF Consortium Page: 8-6

46 A total of four reference points, corresponding to the following (very) large airports have been taken into account in all VHF channel occupancy evaluations using the NAVSIM tool:! Brussels (EBBR)! London/Heathrow (EGLL)! Frankfurt (EDDF)! Munich (EDDM) Note: The name of the reference point (= airport reference point; e.g. Brussels/National (EBBR)) is indicated in the header of the VHF channel occupancy result graphics as depicted in Figure 8-1 to Figure 8-6 below VHF Channel Occupancy / Interference Results and Statistics In the VHF Channel Occupancy calculations produced by NAVSIM the following data / statistics are contained:! Selected reference point (e.g. EBBR) and the range of interest (e.g. 200 nm)! Selected threshold values 11 ranging from -95 dbm to -70 dbm in 5 db steps (input parameter)! Assumed parameters of the interfering transmitters (EIRP) and a victim receiver (antenna gain, cable loss)! Received power in dbm at the input of a victim receiver, separately for each of the 760 VHF channels in the VHF band ( MHz to MHz) (output)! Distance between the selected reference point and the VHF station (ground station or airborne station) that has produced maximum interference power at the input of the victim receiver)! Distance between the victim receiver (observation point) and the VHF station (ground or airborne) that has produced maximum interference power at the input of the victim receiver) Note: In the graphics as depicted in Figure 8-1 to Figure 8-6 below, signal levels are shown in the following colours: Red: received signal power is above the threshold value; Yellow: received signal power is below the threshold value; in this case, the background is depicted in dark green to identify "available" channels easier; Light green: no received power calculated (either all VHF stations were beyond radio horizon (BRH) or no VHF station information was available for this VHF channel).! Maximum received signal power in dbm observed over all VHF channels! Minimum received signal power in dbm observed over all VHF channels! Absolute number and percentage of "available" channels (i.e. below the. threshold value) 11 Several threshold values have been defined as reference for further VHF channel occupancy investigations Copyright B-VHF Consortium Page: 8-7

47 ! Absolute number and percentage of "occupied" channels (i.e. above the threshold value)! Distribution of the number of consecutive channels with received power below threshold value! Mean value of received signal power in dbm of all VHF channels above the threshold value. In order to illustrate the principle approach of the VHF channel occupancy evaluations as described in Subsections 8.2 to 8.5 above, examples of the simulated/calculated VHF interference scenarios using the NAVSIM tool are depicted in Figure 8-1 to Figure 8-6, respectively. Copyright B-VHF Consortium Page: 8-8

48 Figure 8-1 depicts the results of the VHF Channel Occupancy Calculation for Brussels/National (EBBR) Airport. The reference point was put at airport height and the thresholds used for evaluation range from -95 dbm to -85 dbm. Figure 8-1: VHF Channel Occupancy Calculation for Brussels/National Airport (1) Note: The obtained VHF channel occupancy statistics (depicted in Figure 8-1 to Figure 8-6), especially the percentage of "available" VHF channels (for which only received signal power below the threshold value has been calculated), as well as the number of consecutive (adjacent) "available" VHF channels is of interest for the B-VHF design and further analysed in Section 9 of this document. Copyright B-VHF Consortium Page: 8-9

49 Figure 8-2 depicts the results of the VHF Channel Occupancy Calculation for Brussels/National (EBBR) Airport. The reference point was put at airport height and the thresholds used for evaluation range from -80 dbm to -70 dbm. Figure 8-2: VHF Channel Occupancy Calculation for Brussels/National Airport (2) Note: At the Brussels Airport (ground level) around 75% of the VHF channels between MHz and 137 MHz are indicated as "available" for the B-VHF overlay concept if a threshold value of -75 dbm is used as reference. Copyright B-VHF Consortium Page: 8-10

50 Figure 8-3 depicts the results of the VHF Channel Occupancy Calculation around Brussels/National (EBBR) Airport. The reference point has been put at an altitude of feet whilst the victim receivers are set with in area of 20 nm around the airport and the thresholds used for evaluation range from -80 dbm to -70 dbm. Figure 8-3: VHF Channel Occupancy Calculation for Brussels/National Airport (3) Note: In an area of 20 nm around the Brussels Airport and in an altitude of feet around 50% of the VHF channels between MHz and 137 MHz are indicated as "available" for the B-VHF overlay concept if a threshold value of -75 dbm is used as reference. Copyright B-VHF Consortium Page: 8-11

51 Figure 8-4 depicts the results of the VHF Channel Occupancy Calculation around Brussels/National (EBBR) Airport. The reference point has been put at an altitude of feet whilst the victim receivers are set with in area of 60 nm around the airport and the thresholds used for evaluation range from -80 dbm to -70 dbm. Figure 8-4: VHF Channel Occupancy Calculation for Brussels/National Airport (4) Note: In an area of 60 nm around the Brussels Airport and in an altitude of feet around 35% of the VHF channels between MHz and 137 MHz are indicated as "available" for the B-VHF overlay concept if a threshold value of -75 dbm is used as reference. Copyright B-VHF Consortium Page: 8-12

52 Figure 8-5 depicts the results of the VHF Channel Occupancy Calculation around Brussels/National (EBBR) Airport. The reference point has been put at an altitude of feet whilst the victim receivers are set with in area of 60 nm around the airport and the thresholds used for evaluation range from -80 dbm to -70 dbm. Figure 8-5: VHF Channel Occupancy Calculation for Brussels/National Airport (5) Note: In an area of 60 nm around the Brussels Airport and in an altitude of feet around 35% of the VHF channels between MHz and 137 MHz are indicated as "available" for the B-VHF overlay concept if a threshold value of -75 dbm is used as reference. A comparison with the results depicted in Figure 8-4 shows that the significant higher altitude ( feet versus feet) indicates that the altitude has (almost) no impact on the percentage of "available" VHF channels. Copyright B-VHF Consortium Page: 8-13

53 Figure 8-6 depicts the results of the VHF Channel Occupancy Calculation around Brussels/National (EBBR) Airport. The reference point has been put at an altitude of feet whilst the victim receivers are set with in area of 200 nm around the airport and the thresholds used for evaluation range from -80 dbm to -70 dbm. Figure 8-6: VHF Channel Occupancy Calculation for Brussels/National Airport (6) Note: In an area of 200 nm around the Brussels Airport and in an altitude of feet almost all VHF channels between MHz and 137 MHz are indicated as "occupied" even for a threshold value of -75 dbm. The immediate conclusion from this is, that the B-VHF overlay concept can be applied (in areas like Brussels Airport with a high density of VHF stations) only if B-VHF cells with a range smaller than 200 nm are defined, as further analysed in detail in Section 9 of this document Comparison of VHF Channel Occupancy Calculations and Measurements In order to gather important reference data for the B-VHF system design, two B-VHF measurement flight campaigns have been carried out on July 8/9 and on August 31/September 1 in summer A detailed description of these B-VHF measurement Copyright B-VHF Consortium Page: 8-14

54 flights is contained in [B-VHF D12]. Each B-VHF measurement flight campaign consisted of tree flights: a) Transition flight from Tees-side (EGNV) to Southend (EGMC) at FL160 ( feet) b) Main measurement flight (first and second campaign) from Southend (EGMC): 1. to Cambridge (EGSC) with circles (30 nm, 20 nm and 10 nm) around Bovingdon VOR at FL 160 ( feet), FL 260 ( feet) and FL 340 ( feet) Central London Area. 2. to Bornemouth (EGHH), via Belgium, France (Paris, Bretagne), and South England at FL 280 ( feet) Central European Airspace / Reference Area (see Figure 7 5). c) Transition flight from Cambridge (EGSC) or Bornemouth (EGHH) respectively back to Tees-side (EGNV) at FL 160 ( feet). For further evaluation purposes, each B-VHF measurement flight was segmented into sections of 5 minutes duration as depicted for the second main B-VHF measurement flight from Southend (EGMC) to Bornemouth (EGHH) on Sep.1, 2004 as shown in Figure 8-7. Figure 8-7: B-VHF Flight from Southend to Bornemouth on Sep. 1, 2004 Copyright B-VHF Consortium Page: 8-15

55 Comparison of VHF Channel Occupancy Calculations with B-VHF Measurement Flights For further VHF channel occupancy evaluation, the following procedure has been applied:! A victim receiver was assumed to be on board of the B-VHF measurement flight for comparison / validation purposes between calculated VHF channel occupancy and VHF channel occupancy obtained from B-VHF flight measurements using a spectrum analyzer on board of the measurement aircraft (see B-VHF deliverable [B-VHF D12] for details).! For each 5 minutes section the maximum received signal power at the assumed victim receiver has been calculated using NAVSIM for each of the khz VHF channels in a similar way as described in Subsection 8.2 above.! For each 5 minutes section the maximum received signal power as measured and recorded by the spectrum analyzer on board of the measurement aircraft for each of the khz VHF channels has been determined using NAVSIM.! From this calculated / measured received signal power the data statistics as described below have been retrieved. For each 5 minute segment of the measurement flight, VHF channel interference / occupancy calculations and statistics are produced by NAVSIM as outlined in Subsection 8.6 above. An example of the graphical representation of the calculated / measured VHF channel statistics is shown in Figure 8-8. This figure illustrates a comparison of the calculated VHF Channel Occupancy results with the results obtained from the measurements for the B-VHF Measurement Flight on Sep.1, 2004 at 07:20 UTC and at an altitude of feet over Wattisham (EGUW). The evaluated thresholds depicted in Figure 8-8 are -85 dbm and -80 dbm. The results indicate that during a 5 minute period (07:15 to 07:20) of the second main B-VHF measurement flight around 90 % of VHF channels are indicated as "available" for a threshold value of above -80 dbm, while the VHF channel occupancy calculations indicate a percentage of only around 50 % for this threshold. This is due to the fact, that in the calculations a 100 % duty cycle of all the VHF frequencies allocated to VHF stations within the radio horizon and worst case positions of possibly interfering airborne VHF stations (see Subsection 8.2 above) are assumed. Consequently, the number of "none occupied" consecutive adjacent channels with regard to the measurements is significantly larger than in the calculations (e.g. for threshold of -80 dbm: one occurrence of 66 consecutive channels (B-VHF Flight 12 ), compared to one occurrence of 9 consecutive channels (VHF calculations). 12 In Figure 8-8 the "upper" (positioned) numbers relate to the B-VHF flight and the "lower" (positioned) numbers to the VHF calculations. Copyright B-VHF Consortium Page: 8-16

56 Figure 8-8: Comparison of calculated VHF Channel Occupancy and measured Results Comparison of Measured and Calculated Received Signal Power In addition, especially for comparison and validation purposes of the VHF channel occupancy / interference calculations with the measurement data, the following procedure has been carried out: Whenever a received signal power higher than -80 dbm 13 has been measured and recorded during a time period of 15 seconds, the corresponding received signal power is calculated and stored, taking the following into account:! Position and altitude of the measurement aircraft at the time when the received signal power above -80 dbm is measured (labelled as "B-VHF Flight", depicted as (blue) squares in Figure 8-9 to 8-15).! Put the victim receiver (assumed to be on board of the aircraft) at exactly the position of the measurement aircraft when the received signal power above -80 dbm is measured. 13 A value of -80 dbm has been chosen to distinguish signal from noise or weak interferers. Copyright B-VHF Consortium Page: 8-17

57 ! Calculate the maximum received signal power for the VHF channel on which the measured signal has been received, taking all VHF ground stations 14 (position, type 15, supported service, etc.; as described in Subsection 8.2 above) stored in the data bases into account (labelled as "VHF Calculation", depicted as (green) circles in Figure 8-9 to 8-15).! Indicate the distance (in nm) from the VHF station to the victim receiver (labelled as "Station distance", depicted as (red) circles in Figure 8-9 to 8-15)! Calculate the difference between the measured and the calculated received power of specially selected VHF channels (e.g. broadcast VHF channels offering ATIS and VOLMET services to avoid the impact of airborne VHF stations) for each measurement flight Example Discussion and Verification of Measured and Calculated Received Power In order to validate the! Free-Space Propagation model! VHF station parameters (Airport, TMA, En-route) and Receiver Characteristics! Model and parameter implementations in NAVSIM used for VHF channel occupancy / interference evaluation as an important basis for the B-VHF system design, comparisons of the calculated and measured received power level values of all VHF channels between 118 MHz to 137 MHz for all B-VHF measurement flights have been carried out. In this subsection, several examples of comparisons between the measured and the calculated received power for VHF channel occupancy / interference calculations are discussed in detail, including especially VHF stations offering broadcast information services (ATIS and VOLMET). The comparison between the measured and the calculated received power depicted in Figure 8-9 below show very good correspondence for the VHF frequency MHz, (Amsterdam Schiphol) for distances between around 30 nm up to 100 nm. For distances below 30 nm, the measured received power is lower (difference > 5 db) than the calculated values. It is assumed that reasons for this observation are the antenna characteristics of the VHF ground stations with lower EIRP values directly above the station. But the calculated values are higher than the measured ones (worse case situation), which is important for further B-VHF system design. This observation can be made for several of the investigated VHF channels in the whole range from 118 to 137 MHz. 14 For comparison and validation purposes the airborne VHF stations at worst case positions are excluded. 15 Airport VHF stations correspond to "Type 0", TMA VHF stations to "Type 1" and Enroute VHF stations to "Type 2" in NAVSIM statistics and examples graphics below. Copyright B-VHF Consortium Page: 8-18

58 Figure 8-9 depicts the results of the comparison of calculated and measured received power during the B-VHF Measurement Flight from Southend (EGMC) to Bournemouth (EGHH) carried out on September 1 st, 2004 for VHF channels and Figure 8-9: Comparison of calculated and measured received power (1) NOTE: In the figures, on the x-axis, the time of the day is indicated in fractions of hours, i.e correspond to 8 hours and 30 minutes (UTC). The VHF station, with frequency, type and name is indicated in the header; during the measurement flight it can happen, that depending on the position of the aircraft - different VHF stations appear as nearest VHF station at the same frequency. A comparison for VHF frequency MHz (Tees-side ATIS), which is assumed to be a VHF TMA type station (50 Watt transmit power, EIRP = 46 dbm) show (see Figure 8-10) that several measured values are below the calculated values, but towards the end of the flight (at distances even close to 0 nm) a very good correspondence between the calculated and the measured received power values (except for the last few samples) is achieved, which could be related to the attitude of the aircraft (aircraft is landing in Teesside) and thus the orientation of the aircraft antenna. It is known, that the free space propagation model (described in above) used in the VHF channel calculations, is less accurate as closer the aircraft (the victim receiver) is to the ground, which is the case for the measured / calculated values in the in the landing scenario investigated here. While the Tees-side ATIS VHF TMA type station shows some differences between the measured and the calculated received power, as described above and shown in Figure 8-10, the airport type VHF station (10 W transmit power; EIRP = 39 dbm) shows quite good correspondence between the measured and the calculated received power, especially for distances around 50 nm and short before landing (see Figure 8-11). NOTE: In the overall evaluation and comparison of the measured values in all flights with the calculated received power, it was observed that especially when a transmit power of 50 Watt (EIRP = 46 dbm) was assumed for the ATIS stations, the calculated received power was almost in all cases and scenarios a few db above the measured value. Copyright B-VHF Consortium Page: 8-19

59 Figure 8-10 depicts the results of the comparison of calculated and measured received power during B-VHF Measurement Flight from Cambridge (EGSC) to Tees-side (EGNV) carried out on July 9 th, 2004 for the VHF channel MHz (Tees-side ATIS). Figure 8-10: Comparison of calculated and measured received power (2) An example of an Airport type VHF station is contained in Figure 8-11 showing the measurement and calculation results for VHF frequency MHz (London Heathrow). While the measurement aircraft circles around the Bovingdon (BNN) VOR, the distance to the VHF station at London Heathrow periodically decreases and increases and thus both the measured as well as the calculated received power increases and decrease accordingly, whereas the received signal level remains always slightly below the calculated signal level which is well justified taking reasonable worse case assumptions for the B-VHF system design into account. Figure 8-11 depicts the results of the comparison of calculated and measured received power during B-VHF Measurement Flight from Southend (EGMC) to Cambridge (EGSC) carried out on July 9 th, 2004 for VHF channel MHz (London Heathrow, Tower Airport VHF station). Figure 8-11: Comparison of calculated and measured received power (3) A further comparison between the measured and calculated values for an ATIS VHF TMA type station are depicted in Figure 8-12 which shows the results for the Farnborough (EGLF) ATIS station transmitting at VHF frequency MHz during the B-VHF Measurement Flight from Southend (EGMC) to Cambridge (EGSC) carried out on July 9th, In most cases the measured values are a few db below the calculated values which confirms the assumption of a worse case but not too worse scenario, if a transmit power of 50 Watt (EIRP = 46 dbm) is used in the calculations for TMA type ATIS broadcast VHF stations. Copyright B-VHF Consortium Page: 8-20

60 Figure 8-12 depicts the results of the comparison of calculated and measured received power during B-VHF Measurement Flight from Southend (EGMC) to Cambridge (EGSC) carried out on July 9 th, 2004 for the VHF channel Farnborough ATIS at MHz. Figure 8-12: Comparison of calculated and measured received power (4) Figure 8-13 depicts the results of the comparison of calculated and measured received power during B-VHF Measurement Flight from Southend (EGMC) to Bournemouth (EGHH) carried out on Sept.1, 2004 for VHF channel MHz (ATIS Münster/Osnabrück), and Figure 8-13: Comparison of calculated and measured received power (5) Copyright B-VHF Consortium Page: 8-21

61 While the measured values are lower than the calculated values by around 10 db for the London Stansted (EGSS) ATIS at MHz, the Paris/Toussus-Le-Nob (LFPN) at and the Melun/Villaroche at MHz, a very good correspondence for the measured and calculated values can be observed for the Münster/Osnabrück ATIS VHF station in Germany at MHz. Further examples of measured values of ATIS VHF broadcast stations recorded during the B-VHF measurement flight from Southend (EGMC) to Bournemouth (EGHH) on Sept. 1, 2005, are depicted in Figure 8-14 and Figure In Figure 8-14 also the Amsterdam/Schipol VHF ATIS station at shows a quite good match between the measured and the calculated values for distances to the VHF station of down-to around 30 nm. Again as explained already above - it is assumed, that the deviation of the measured values from the calculated values is caused by the shape of the antenna propagation characteristics of the VHF ground station due to lower EIRP values directly above the station. Figure 8-14: Comparison of calculated and measured received power (6) Beside the ATIS VHF stations, special attention has also been put on the VOLMET ACC stations. Figure 8-15 depicts the results of the comparison of calculated and measured received power during the B-VHF Measurement Flight from Tees-side (EGNV) to Southend (EGMC) conducted on July 8 th, 2004 for VHF channels MHz and MHz (London VOLMET ACC). For the time period of the flight between 15:36 UTC 16 and 16:12 UTC 17 a very good correspondence between the measured and the calculated values is shown for the London VOLMET ACC frequency at MHz. A deviation of the calculated values from the measured values can be observed however for the time period after 16:12 UTC. A comparison with the GPS flight track data depicted in Figure 8-16 below shows however, that at this time the B-VHF measurement flight, landing in Southend (EGMC) had already a (low) altitude of below feet. It is assumed that the fact that the aircraft is already close to the ground is the reason for the deviation of the calculated VHF values based on the free space propagation model (see ) from the measured values during the final phase of the landing scenario. 16 Corresponds to 15.6 on the x-axis for MHz 17 Corresponds to 16.2 on the x-axis for MHz Copyright B-VHF Consortium Page: 8-22

62 Figure 8-15 contains the results of the comparison of calculated and measured received power during the B-VHF transition flight Tees-Side (EGNV) to Southend (EGMC) carried out on July 8 th, 2004 for VHF channel MHz and MHz (VOLMET London ACC). Figure 8-15: Comparison of calculated and measured received power (7) Copyright B-VHF Consortium Page: 8-23

63 Figure 8-16 shows the GPS track of the B-VHF transition flight from Tees-Side (EGNV) to Southend (EGMC) carried out on July 8 th, At 16:12 UTC the B-VHF measurement flight has descended from FL 160 ( feet) to an altitude of feet. Figure 8-16: B-VHF Flight from Tees-Side to Southend, on July 8, 2004, 16:12; feet Statistics of Comparison between Calculations and Measurements In order to retrieve an overall statistical reference value for the comparison of the calculated received signal power using a Free-space Propagation Model (see Subsection ) as basis for the VHF channel occupancy calculations with the measured received signal power during each of the six transition/measurement flights (see introduction to Subsection 8.7 above) the following approach has been applied:! Whenever a received signal power higher than -80 dbm has been measured and recorded during a time period of 15 seconds - in any of the VHF channels between 118 MHz and 137 MHz - the corresponding received signal power is calculated and stored (see above)! In order to eliminate the impact of transmitting airborne VHF stations, for which the position and time of transmission is unknown during the measurement flight and therefore not taken into account in the corresponding calculations which are Copyright B-VHF Consortium Page: 8-24

64 based on assumed transmissions of nearest VHF ground station only, for further statistics, focus is put on: " ATIS TMA type VHF stations (for reasons of VHF ground station broadcast transmissions only no airborne stations involved) as well as " Airport type VHF stations (due to the fact that possibly transmitting airborne VHF stations are almost co-located with the airport type VHF ground station due to small dimensions of the covered airport area and the fact, that airborne VHF stations transmit with only a slightly higher EIRP of 41 dbm compared to the assumed EIRP of airport VHF stations of 39 dbm).! For each of the measurement flights and for all VHF frequencies corresponding to these ATIS TMA type VHF stations as well as for the Airport type VHF stations, common statistical values are retrieved as follows: " The median of all measured received power values (above -80 dbm) of all these ATIS and Airport type VHF frequencies is calculated over the whole measurement flight " The median of all calculated received power values corresponding to each of the measured received power values is calculated over the whole duration of the measurement flight! The median of the measured and calculated received power values for each of the B-VHF measurement flights is printed in Table 8-2 below. Copyright B-VHF Consortium Page: 8-25

65 B-VHF Measurement Flight Tees-side (EGNV) to Southend (EGMC) Southend (EGMC) to Cambridge (EGSC) Cambridge (EGSC) to Tees-side (EGNV) Tees-side (EGNV) to Southend (EGMC) Southend (EGMC) to Bournemouth (EGHH) Bournemouth (EGHH) to Tees-side (EGNV) Date Time (UTC) Median of measured received power Median of calculated received power Median of calculated values higher than measured values (in db) July 8,'04 15:11 16: July 9,'04 06:39 11: July 9,'04 12:21 13: Aug.31,'04 14:57 15: Sep.1,'04 06:55 09: Sep.1,'04 11:44 12: Table 8-2: Median of Measured and Calculated Received Power of ATIS and Airport VHF Stations As shown in Table 8-2 above, the fact that the median of the calculated received power (using a Free-space Propagation Model, see ) is always higher (between 3.9 and 7.3 db) compared to the median of the measured received power corresponds to an appropriate worse case assumption for further B-VHF system design based on calculated VHF channel occupancy and interference. These statistics are also consistent with the results described in detail in Subsection above Conclusions for Validation From the comparison of the received signal power measured and recorded by a spectrum analyser during the B-VHF measurement flights and the calculated received power, the following conclusions can be drawn:! Measured and calculated values show a good correspondence in many cases for larger distances (e.g. > 30 nm) between the measurement aircraft / victim receiver and the VHF station.! The calculated received power (in dbm) is often a few db higher (e.g. larger than 5 db) than the measured received power if the VHF station is directly over-flown by the measurement aircraft. This can be explained by the antenna propagation characteristics of VHF ground stations (smaller EIRP values directly above the station).! If the measurement aircraft is landing at an airport, and therefore close to the altitude of the VHF station positioned at this airport, the measured and calculated values show a good correspondence in most cases. Copyright B-VHF Consortium Page: 8-26

66 ! The assumption of a transmit power of 50 Watt (corresponding to an EIRP of 46 dbm) for VHF En-route stations and a transmit power of 10 Watt (corresponding to an EIRP of 39 dbm) for VHF Airport stations is well justified by the comparison of the calculated with the measured values in most cases.! In most cases the calculated values are higher than measured values, which correspond to an appropriate worse case assumption for further B-VHF system design based on calculated VHF channel occupancy and interference. As an overall conclusion it can be stated, that the usage of a free-space propagation model for worse case assumptions of VHF channel interference / occupancy calculations using NAVSIM are quite well validated by the B-VHF flight measurement results. The B- VHF measurements show reasonable and expected results in most cases. For further B- VHF evaluations, it is intended to investigate and apply refined propagation models (e.g. two ray model including ground reflections) to take also some observed fading effects into account Assessment of B-VHF System Performance using NAVSIM Further detailed B-VHF System performance evaluations using NAVSIM will take the following ATC frequency association for each of the simulated flights into account:! Determine flight phase (Communications at departure gate, taxiing to departure runway, departure, departure route (climb phase), en-route phase, arrival/approach phase, landing, taxiing to destination gate, communications at destination gate)! Identify current ATC sector, depending on location (geographical coordinates) and altitude.! Associate VHF frequency assigned to ATC sector, or! Take appropriate VHF frequency / frequencies according to current flight phase into account (e.g. communications with Ground / Apron Control at departure gate, etc.)! Generate voice / data traffic according to flight phase, aircraft type / airline class, duty cycle statistics, etc.! Compare simulated results and statistics using NAVSIM with radar data and voice recordings provided by NATS for assessment of the B-VHF System performance END OF SECTION Copyright B-VHF Consortium Page: 8-27

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68 9. B-VHF Capacity Analysis In this section, a first capacity analysis of the B-VHF system is carried out. The procedure for the B-VHF capacity analysis is as follows. The capacity analysis is performed based on the results from the worst-case VHF band occupancy simulations which have been carried out using the NAVSIM tool, see Section 8. The worst-case simulations are used rather than the VHF band measurements [B-VHF D12], since the measurement results might be too optimistic for the safety assessment. Based on the worst-case simulations, the maximum allowed B-VHF transmit power is determined in such a way, that interference from the B-VHF system towards the legacy VHF systems is avoided. As detailed in Section 9.5, at least 25% of the VHF band capacity is assumed to be required for the successful introduction of B-VHF as overlay system in the VHF band. In order to achieve respective VHF band capacity values, a certain amount of interference coming from the legacy VHF systems has to be tolerated by the B-VHF system. Based on Signal-to-Noise Ratio (SNR) and Signal-to-Interference Ratio (SIR) considerations, it is evaluated if the B-VHF system is capable to work with the determined maximum B-VHF transmit power in an acceptable manner under the expected narrowband interference from the legacy VHF systems Results from Worst-case Simulations with NAVSIM The goal of the worst-case VHF band occupancy simulations with the NAVSIM tool is to determine the maximum possible interference power levels at a virtual victim receiver for each of the 760 VHF channels of 25 khz bandwidth in the VHF band range from MHz. The maximum interference power levels are calculated taking into account worst-case scenarios for both ground station and aircraft transmissions. For the ground station transmissions the worst-case scenario is to assume that all ground stations transmit on their respective frequency with a duty cycle of 100%. Aircraft are represented by one worst-case interfering aircraft per ATC sector. This aircraft is located at the edge of the ATC sector which is nearest to the victim receiver. Moreover, the duty cycle of the worst-case interfering aircraft is set to 100%. In doing so, the worst possible interference scenarios are created for the VHF band occupancy simulations. The interference power level in each VHF channel is calculated using a link budget analysis based on free space propagation. All aircraft and ground stations within the radio horizon are taken into account assuming the EIRP power levels for transmission as specified in Table 9-1. At the receiver, a loss of 3 db due to cabling, etc. is assumed. Since the victim receiver might see several narrowband signals in each VHF channel, e.g. a ground station and an aircraft transmitter, the strongest interference signal and with that the maximum interference power level is considered. Aircraft EIRP Aerodrome EIRP TMA EIRP En Route EIRP 41 dbm 39 dbm 46 dbm 46 dbm Table 9-1: EIRP levels of the different transmitter types as used in NAVSIM simulations. The VHF channels which can be re-used for B-VHF have to be available not only at a certain geographical point, but within a whole B-VHF cell. For simplicity, B-VHF cells are assumed to be cylindrical and are characterized by their cell radius. In order to take into Copyright B-VHF Consortium Page: 9-1

69 account the influence of different flight levels on the VHF band occupancy, circular disks of the B-VHF cell cylinder at certain flight levels are considered. Within the NAVSIM simulations the maximum possible interference power level within a circular B-VHF cell disk is determined by calculating the interference power at the input of the victim receiver placed at equally spaced observation points on the border of the circular B-VHF cell disk and retaining for each VHF channel the maximum determined interference power level. Munich Airport (EDDM) Cell Radius Flight Level Interference Power Threshold Available VHF Band 20 nm FL dbm 35.7% 20 nm FL dbm 17.6% 20 nm FL dbm 50.0% 20 nm FL dbm 38.8% 20 nm FL dbm 65.5% 20 nm FL dbm 65.7% 20 nm FL dbm 80.8% 20 nm FL dbm 79.1% 60 nm FL dbm 19.7% 60 nm FL dbm 8.4% 60 nm FL dbm 33.0% 60 nm FL dbm 23.6% 60 nm FL dbm 47.0% 60 nm FL dbm 47.1% 60 nm FL dbm 55.4% 60 nm FL dbm 55.0% Table 9-2: Results from the worst-case simulations with NAVSIM for B-VHF cells with different cell size evaluated at different flight levels at Munich airport. Moreover, transmissions from ground stations or aircraft being located within the cylindrical B-VHF cell are treated in such a way that the victim receiver has always been put as near as possible to such transmitters. For more details refer to Section 8 where a detailed description of the NAVSIM tool is given. In Table 9-2 and Table 9-3 the results Copyright B-VHF Consortium Page: 9-2

70 from the worst-case simulations with NAVSIM for B-VHF cells of different size positioned at different locations are summarized. Table 9-2 shows the results for B-VHF cells located at Munich airport, whereas Table 9-3 is valid for B-VHF cells located at Brussels airport. Brussels Airport (EBBR) Cell Size Flight Level Interference Power Threshold Available VHF Band 20 nm FL dbm 24.7% 20 nm FL dbm 6.4% 20 nm FL dbm 39.6% 20 nm FL dbm 24.7% 20 nm FL dbm 50.3% 20 nm FL dbm 50.4% 20 nm FL dbm 67.2% 20 nm FL dbm 67.2% 60 nm FL dbm 12.2% 60 nm FL dbm 3.8% 60 nm FL dbm 19.3% 60 nm FL dbm 9.1% 60 nm FL dbm 34.9% 60 nm FL dbm 34.9% 60 nm FL dbm 46.3% 60 nm FL dbm 46.1% Table 9-3: Results from the worst-case simulations with NAVSIM for B-VHF cells with different cell size evaluated at different flight levels at Brussels airport. For interpretation of the tables, the following example referring to Table 9-2 is given. Consider a cylindrical B-VHF cell with radius 20 nm. At flight levels FL 50 and FL 250, the available bandwidth for a B-VHF system is about 65.5% and 65.7%, respectively, if an acceptable interference power threshold of -75 dbm is assumed. From the tables, some general conclusions can be drawn. If an interference power level of -75 dbm or higher is acceptable, a large available VHF bandwidth for the B-VHF system is available, e.g. around 65% and 47% at Munich airport for small (20 nm) and large (60 nm) B-VHF cells, respectively. Moreover, for these interference power levels Copyright B-VHF Consortium Page: 9-3

71 the available VHF bandwidth is almost independent of the chosen flight level. If the interference power threshold has to be chosen smaller than -75 dbm, the B-VHF cell size has to be reduced and the available VHF bandwidth becomes flight level dependent. Bovingdon VOR Radius of Orbit Flight Level Interference Available VHF Band Power Threshold Segment Half Orbit Whole Orbit 10 nm FL dbm 60.58% 60.58% % 10 nm FL dbm 69.78% 69.78% % 10 nm FL dbm 78.84% 78.84% % 10 nm FL dbm 84.10% 84.10% % 10 nm FL dbm 89.36% 89.36% % 20 nm FL dbm 66.80% 55.52% 44.24% nm FL dbm 74.87% 65.70% 56.53% nm FL dbm 80.82% 74.16% 67.50% nm FL dbm 85.68% 80.93% 76.18% nm FL dbm 89.71% 86.32% 82.93% nm FL dbm 72.68% 58.54% 44.40% nm FL dbm 78.55% 68.26% 57.97% nm FL dbm 82.98% 75.09% 67.20% nm FL dbm 87.16% 81.35% 75.54% nm FL dbm 90.39% 86.41% 82.43% 19 Table 9-4: Results from the 1 st measurement flight performed on different orbits, i.e., flight level and radius, within Bovingdon VOR, UK. 18 Same as segment result, since segment approximately spans half orbit. 19 Value estimated from half orbit result, since not available from measurement data analysis. Copyright B-VHF Consortium Page: 9-4

72 For comparison, results from the VHF occupancy measurement campaign [B-VHF D12] are given in Table 9-4. Especially, the measurement results obtained from the 1st measurement flight performed on 8/9 July 2004 are considered where several orbits on different flight levels within Bovingdon VOR, UK, have been flown:! FL160 30nm radius,! FL260 20nm radius,! FL340 10nm radius. The available percentage of the VHF band is given for different measurements:! A measurement along a certain part of the orbit (segment).! A measurement along approximately half the orbit.! A measurement along the full orbit. A segment spans 1/10, 1/6, and 1/2 of the whole orbit for orbits with 30 nm, 20 nm, and 10 nm radius, respectively. Note, considering the results for the whole orbit corresponds to the results for a B-VHF cell with cell radius equal to the orbit radius. As can be seen from Table 9-4, the percentage of the available VHF band is considerably higher for the measurements than for the worst-case simulations. For example, comparing the measurement results for a whole orbit with 20 nm radius (FL 260) at interference power thresholds set to -70 dbm and -86 dbm with the worst-case simulations for a B-VHF cell with radius 20 nm, FL 250, and interference power thresholds set to -70 dbm and -85 dbm results in 82.93% and 44.24% versus 67.2%/79.1% (EBBR/EDDM) and 6.4%/17.6% (EBBR/EDDM), respectively. A conservative design is required to ensure that interference from the B-VHF system towards the legacy VHF systems is definitely avoided. Therefore, the B-VHF system design is based on the results of the worst-case simulations. However, as shown by the comparison of the worst-case simulations with the measurement results it is expected that the realistic interference from the legacy VHF systems towards the B-VHF system is considerably less than the worst-case simulations indicate. In the next section, the B-VHF system parameters are determined in such a way, that interference from the B-VHF system towards the legacy VHF systems is avoided. Moreover, it is evaluated if the B-VHF system is able to work with that parameter setting in an acceptable manner. Note, for the determination of the interference from the B-VHF system towards the legacy VHF systems the results from the worst-case simulations with NAVSIM can also be used, since the transmission channel is reciprocal. Especially, the transmission power of the B-VHF system can be calculated which guarantees that legacy VHF systems are not disturbed by the B-VHF system B-VHF System Design with Respect to Interference Avoidance Towards Legacy Systems The first task in this section is determining the maximum allowed transmission power for the B-VHF system which guarantees that the legacy VHF systems are not disturbed. All VHF channels which are below the interference power thresholds as given in Table 9-2 and Table 9-3 might be used for the transmission within the considered B-VHF cell. Note, for determining the mutual interference between B-VHF and legacy VHF systems airborne transmissions and receptions are the critical case and, therefore, only these are considered in the following. After determination of the B-VHF transmission power both Copyright B-VHF Consortium Page: 9-5

73 the SNR and the SIR at a B-VHF receiver are calculated. Finally, conclusions with respect to the B-VHF system design are given. The investigations in this section are all based on a standard link budget analysis. As transmit power for both the B-VHF and the legacy VHF systems the EIRP is considered which already includes losses between the transmitter and its antenna as well as the transmitter antenna gain. For the receiver no antenna gain (0 dbi) and fixed cable losses (3 db) are assumed. All received powers always refer to the input of the receiver and 25 khz bandwidth. Note, this is the same link budget setting as used for the NAVSIM simulations. In order to calculate the maximum allowed transmission power for the B-VHF system the smallest possible distance to a victim receiver of the legacy VHF system has to be determined. Moreover, the interference power level has to be known which is acceptable for the victim receiver, i.e., which guarantees that the normal communications performance of the victim receiver is not degraded. As victim receiver a standard DSB- AM receiver is considered with an acceptable interference power level of -95 dbm 20 within 25 khz bandwidth. Note, all power values for DSB-AM as well as for B-VHF are referred to a bandwidth of 25 khz in the following. The transmission power (EIRP) of the DSB-AM transmitter is known and given in Table 9-1, e.g. EIRP DSB-AM = 41 dbm for an airborne transmitter. Because the EIRP of the DSB- AM transmitter is known, it is easy to determine the distance between DSB-AM interferer and B-VHF victim receiver, as soon as the interference power level at the B-VHF receiver is known which is produced by that DSB-AM interferer. The worst-case interference power levels at the victim B-VHF receiver are available from the NAVSIM simulations. In the following, an example is given for the determination of the maximum allowed transmission power for the B-VHF system and illustrated in Figure 9-1. Consider an interference power threshold of -75 dbm and a cell radius of 20 nm for the B-VHF system. This corresponds according to Table 9-2 to an available VHF bandwidth of around 65% for a B-VHF cell located at Munich airport. Using the standard link budget P = EIRP L a, (9.1) Rx DSB-AM free Rx where P Rx = 75 dbm the interference power level at the B-VHF receiver is produced by the nearest possible DSB-AM interferer, a Rx = 3 db comprises the losses at the B-VHF receiver, and L free is the free space propagation loss L free 4π d f = 20log c, (9.2) the distance d between the B-VHF victim receiver and the nearest possible DSB-AM 8 interferer can be calculated taking into account that c = 310 ms is the speed of light and f = 137 MHz is the carrier frequency of the transmission 20 Currently, 14 db SIR are requested at the DSB-AM receiver. With the B-VHF system being the interference source, we consider 10 db SIR sufficient, since the actual bandwidth of an airborne receiver is less than 25 khz. Moreover, the spectrum of the B- VHF signal is flat (AWGN like) within that bandwidth and, thus, there is no strong carrier component that could open the squelch barrier of the DSB-AM receiver. Copyright B-VHF Consortium Page: 9-6

74 L = EIRP P a = 113 db, (9.3) free DSB-AM Rx Rx c Lfree d = km 42 nm 4π f = =. (9.4) That means for our example, that the smallest possible distance between a DSB-AM and a B-VHF aircraft which use the same VHF channels is 42 nm. Since the maximum acceptable interference power level I max for the DSB-AM system is known (previously selected as I max = 95 dbm ), the maximum allowed B-VHF transmit power (EIRP B-VHF ) per 25 khz bandwidth can be calculated from EIRP = I + L + a = 21 dbm. (9.5) B-VHF max free Rx B-VHF Cell Threshold: -75 dbm (65% weak) 20 nm 42 nm Cell Center B-VHF A/C DSB-AM A/C dbm dbm 41.0 dbm dbm 21.0 dbm dbm 24.4 dbm dbm dbm Figure 9-1: Calculation of the maximum allowed B-VHF transmission power and the resulting SIR at a B-VHF receiver for a B-VHF cell radius of 20 nm and an interference power threshold of -75 dbm. Our example with a B-VHF cell radius of 20 nm and an interference power level of -75 dbm which is assumed to be acceptable for the B-VHF system is summarized in Figure 9-1. The nearest transmitting DSB-AM aircraft must be 42 nm away from the B-VHF aircraft to produce an interference power level of -75 dbm, since it transmits with an EIRP of 41 dbm. The B-VHF aircraft is allowed to transmit in all VHF channels which are received with an interference power level of -75 dbm or less. Thus, the nearest DSB-AM victim receiver is 42 nm away from the B-VHF transmitter. In order to guarantee an interference power level less than I max = 95 dbm at the DSB-AM victim receiver, the B- VHF transmission power (EIRP) is restricted to 21 dbm per 25 khz channel. The B-VHF ground station is allowed to transmit with slightly more power, i.e. with 24.4 dbm EIRP per 25 khz channel, since it is farer away from the DSB-AM victim receiver than the B- VHF aircraft by 20 nm. Knowing the transmit power of the B-VHF system, both the SNR Copyright B-VHF Consortium Page: 9-7

75 and the SIR for the B-VHF system can be calculated. In our example, the SNR at the B- VHF aircraft in absence of interference from the DSB-AM system is around 34.7 db, whereas the SIR is about db, see Table 9-5. That means, as long as there is no interference from the DSB-AM system towards the B-VHF system, a very good transmission quality (SNR > 25 db!) is achieved with the B-VHF system. Simultaneously, it is guaranteed that DSB-AM transmissions are not disturbed, since the B-VHF transmit power is chosen in such a way that the maximum possible interference level at the input of the nearest DSB-AM victim receiver is below I max = 95 dbm. However, if a VHF channel within the transmission bandwidth of the B-VHF system is used by the DSB-AM system, severe interference might occur. This interference is restricted to a small bandwidth of around 25 khz and, thus, influences only a limited number of B-VHF subcarriers. However, these sub-carriers might be lost and not be able to be recovered, since the SIR might be as high as db. A more detailed analysis of the interference from the DSB-AM system towards the B-VHF system is given in Section 9.3. In Table 9-5 the maximum allowed B-VHF transmit power for different scenarios, i.e., different B-VHF cell radii and different interference power thresholds at the B-VHF victim receiver, are summarized. Moreover, the resulting minimum SNR and minimum SIR at the B-VHF aircraft are given. The results are related to Table 9-2 and Table 9-3 where the available bandwidth for B-VHF systems located at Munich and Brussels airport, respectively, is reported for the same scenarios. Cell Radius Interference Power Threshold Distance Between Aircraft EIRP B-VHF Aircraft EIRP B-VHF Ground Min. SNR Min. SIR 20 nm -85 dbm 134 nm 31.1 dbm 32.3 dbm 42.6 db +7.8 db 20 nm -80 dbm 75 nm 26.0 dbm 28.1 dbm 38.4 db -1.4 db 20 nm -75 dbm 42 nm 21.0 dbm 24.4 dbm 34.7 db db 20 nm -70 dbm 24 nm 16.1 dbm 21.4 dbm 31.7 db db 60 nm -85 dbm 134 nm 31.1 dbm 34.3 dbm 35.1 db +0.3 db 60 nm -80 dbm 75 nm 26.0 dbm 31.1 dbm 31.9 db -8.0 db 60 nm -75 dbm 42 nm 21.0 dbm 28.7 dbm 29.5 db db 60 nm -70 dbm 24 nm 16.1 dbm 27.0 dbm 27.8 db db Table 9-5: Maximum allowed B-VHF transmit power (aircraft and ground station) as well as resulting SNR and SIR at the B-VHF aircraft for different scenarios at Munich airport Estimation of Available B-VHF System Capacity In the previous section, the maximum allowed transmit power levels for different scenarios for the B-VHF aircraft as well as the B-VHF ground stations are determined which guarantee that the legacy VHF systems are not disturbed by the B-VHF overlay system. Moreover, the corresponding SNR and SIR at the B-VHF receiver are calculated. Copyright B-VHF Consortium Page: 9-8

76 From these results it can be concluded, that it is possible to establish a B-VHF overlay system in the VHF band having reasonable SNR. In order to have available a significant amount of VHF bandwidth for the B-VHF overlay system, it is necessary to allow a certain interference power from the legacy VHF system towards the B-VHF system. However, powerful interference suppression methods are available at the B-VHF receiver, which are capable of significantly reducing the interference coming from the legacy VHF systems [B-VHF D18]. Our proposal for the B-VHF system design is to use B-VHF cell radii ranging from nm depending on the location of the B-VHF cell. In areas with dense VHF occupancy like Brussels airport, see Table 9-3, smaller B-VHF cell radii (20-60 nm) are recommended, whereas in less dense areas larger B-VHF cell radii ( nm) are possible. In remote areas and over oceans very large cell radii are possible (up to 200 nm and beyond). With respect to the interference power threshold we recommend to allow a quite large value of around -75 dbm. On the one hand, such interference power threshold setting guarantees that the required VHF bandwidth to establish a B-VHF overlay system will be practically available. On the other hand, it is expected that the B-VHF overlay system would be able to cope with such large interference power levels according to the following considerations. First, the system design introduces diversity and, thus, robustness against narrowband interference by applying spreading and coding [B-VHF D18]. Second, powerful interference suppression methods are available which are applied at the B-VHF receiver [B-VHF D18]. And third, it has to be taken into account that the interference considered in the previous section is the worst-case interference, based on the worstcase constellation of interferers. In reality, the spatial constellation of interferers does not correspond to the worst-case and, thus, the received interference power levels are lower. Moreover, the interferers show a certain duty cycle, i.e., the interference from the legacy VHF systems is not present all the time. These facts have already been shown in Section 9.1 where the worst-case simulations are compared to the results of the measurement campaign. The final verification, that the choice of -75 dbm as interference power threshold is reasonable, can not be given at the current stage of the project. This can be done only after having implemented the JAVA simulations. At the current stage of the project, we expect that an interference power threshold of -75 dbm is acceptable for the B-VHF overlay system. This leads to the following estimation of available bandwidth for B-VHF communications:! High density area, e.g. Brussels airport: 35-50% (cell radius nm) of the VHF band, see Table 9-3.! Dense areas, e.g. Munich airport: 47% (cell radius 60 nm) of the VHF band, see Table 9-2.! Low density areas: Around 50% (cell radius nm), estimated value.! Remote areas: Around 50% (cell radius up to 200 nm), estimated value Measures for B-VHF Capacity Improvement The capacity considerations in the previous sections are based on the assumption that at any point of the B-VHF cell the same set of sub-carriers has to be available for the B-VHF system ground station and aircraft. Capacity improvements are possible if this assumption is loosened. Copyright B-VHF Consortium Page: 9-9

77 At a ground station there is considerably more B-VHF capacity available than determined under the above assumption. First, the ground station is fixed at a certain point and, second, the geographical height of the ground station is low compared to the aircraft. Thus, the ground station can, in principle, use a larger percentage of the VHF band for its forward link transmission than determined in the previous sections. An aircraft sees different sets of available sub-carriers depending on its position within the B-VHF cell. Thus, taking into account the current position of the aircraft, additional transmission capacity can be achieved. A practical approach here is to divide the B-VHF cell in several sectors, e.g. 4 to 8, and to assign sub-carrier sets according to the sector in which the aircraft is currently flying. Note, whereas the forward link performs the transmission for all users jointly, the reverse link is established for each aircraft separately. Thus, taking into account the position of the aircraft and with that different available sub-carrier sets, improves the overall capacity. The quantitative improvement which can be achieved with such an approach can not be estimated from the data currently available. An assessment of the capacity improvement is possible only within the JAVA simulations Summary and Conclusions In Section 9, a first capacity analysis for the B-VHF system is given. This analysis is based on the currently available information already gathered within the B-VHF project and comprises the worst-case simulations performed with the NAVSIM tool as described in Section 8 and the VHF band measurements [B-VHF D12]. Before starting the capacity analysis, the minimum VHF band capacity which is required for successful implementation of B-VHF as overlay system in the VHF band has to be determined. For the following considerations, we assume a B-VHF system with 1 MHz transmission bandwidth and a sub-carrier spacing of f = 2.08 khz which results from putting 12/4 sub-carriers into one 25/8.33 khz VHF channel. The basic transport channel in B-VHF is the so-called Fast Channel (FCH) which requires the simultaneous transmission of 4 modulation symbols. This channel is especially designed for voice communications, i.e. one FCH is required for one B-VHF voice channel. Since spreading (CDMA) with a factor L = 4 is applied in the forward link, at least 16 sub-carriers (4 for each modulation symbol) are needed to establish any voice communication. Note, spreading (CDMA) allows to establish up to L = 4 voice channels simultaneously on the 16 sub-carriers. Thus, with the 16 sub-carriers required for any B-VHF voice communication we get 4 B-VHF voice channels. Under the worst-case assumption that only non-adjacent VHF channels are available for B-VHF transmission, two VHF channels are required to establish 4 B-VHF voice channels, since in this case 4 sub-carriers per VHF channel are used for sidelobe suppression and only 8 sub-carriers remain for the actual B-VHF transmission. From this it follows that the theoretical minimum of required VHF band capacity for a deployable B-VHF system is 2 VHF channels within 1 MHz bandwidth, i.e. 5%. From a practical point of view, 5% seems much to less, since having available only 4 additional voice channels in a B-VHF cell might not be enough for starting a successful B-VHF deployment. Moreover, the interference within the B-VHF transmission bandwidth is quite large in this case. Therefore, we propose to start with a considerably larger required minimum VHF band capacity. In our opinion, a B-VHF system which can offer 20 FCH is a good starting point for B-VHF system deployment. In this case, 20 additional voice channels or any combination of voice and data Copyright B-VHF Consortium Page: 9-10

78 communications which require up to 20 FCH are available in each B-VHF cell. Thus, 25% is in our opinion a reasonable value for the minimum required B-VHF capacity. Considering the results from the worst-case simulations performed with the NAVSIM tool as summarized in Table 9-2 and Table 9-3 it follows that allowing up to -75 dbm interference power from the legacy VHF systems towards the B-VHF system results in a B-VHF capacity well above 25% even for relatively large cells (60 nm) in areas with extremely high aircraft density (EBBR). Thus, an interference power threshold of -75 dbm is assumed in the following. Based on this interference power threshold the minimum distance of a worst-case DSB-AM interferer can be determined, referring to Figure 9-1. Having determined the minimum distance between DSB-AM and B-VHF aircraft the maximum allowed transmit power of a B-VHF aircraft can be calculated which still guarantees that the legacy VHF systems are not disturbed by the B-VHF system. The results of this calculation are given in Table 9-5 for different cell radii. For the considered acceptable interference power threshold of -75 dbm, a maximum allowed transmit power of 21 dbm for a B-VHF aircraft results. Fixing the maximum allowed transmit power to that value guarantees that interference from the B-VHF system towards the legacy VHF systems is avoided. To guarantee successful co-existence between the legacy VHF systems and the B-VHF system, not only the interference from the B-VHF system towards the legacy VHF systems has to be considered, but also the narrowband interference on the B-VHF overlay system caused by the legacy VHF systems. Unfortunately, it is not possible to investigate the influence of this interference on the B-VHF system at the current stage of the project in detail, as it requires the implementation of the B-VHF communications chain. These investigations can only be carried out after the JAVA simulation software has been produced [B-VHF D18]. Currently, only basic SNR and SIR estimates can be given, see Table 9-5, which state the expected SNR for the B-VHF reception in the interference-free case and the expected SIR in the case of worst-case interference from the legacy VHF systems, respectively. Assuming again an interference power threshold of -75 dbm it becomes clear from Table 9-5, that B-VHF communications in the interference free case is of very good quality, since an SNR larger than 25 db is achieved. The remaining question is, if the B-VHF system can cope with the narrowband interference coming from the legacy VHF systems which might result in B-VHF receiver SIR values as low as -15 db. Although a final verification that the B-VHF system is able to cope with the interference produced by the legacy VHF systems cannot be given at the current stage of the project, it is expected that B-VHF can be successfully implemented as overlay system in the VHF band and achieve good transmission quality. There are several reasons for this expectation: The SIR values given in Table 9-5 are worst-case values (min. SIR) which are determined based on the minimum possible distance between B-VHF aircraft and DSB-AM interferers. Taking into account that in many cases the B-VHF aircraft is not at the B-VHF cell boundary but within the B-VHF cell and that the DSB-AM interferers are not at the smallest possible distance to the B-VHF cell, in average the SIR is much less than given in Table 9-5. The interference within a certain VHF channel is not present all the time due to the duty cycle of VHF communications. The SIR values given in Table 9-5 are related to the 25 khz narrowband VHF channels. Considering diversity due to spreading and coding, the resulting effective SIR values are considerably lower. Copyright B-VHF Consortium Page: 9-11

79 Several countermeasures for narrowband interference suppression are available at the B-VHF receiver to further reduce the effect of the interference from the VHF legacy systems on the B-VHF system. Besides an appropriate system design which takes into account spreading and coding in order to achieve a high robustness of the B-VHF system against narrowband interference, several methods are available that can be used for narrowband interference suppression at the B-VHF receiver as described in detail in [B-VHF D18]. The most promising methods are: Analogue time domain methods: These methods are applied before A/D conversion in order to reduce DSB-AM interference from these VHF channels within the B-VHF transmission bandwidth which are not used for B-VHF transmission, i.e. VHF channels which might obtain so-called strong DSB-AM interferers. Although the interference in these channels has only a small direct impact on the data transmission of the B-VHF system, it has to be suppressed in order to guarantee a sufficient dynamic range for A/D conversion of the B-VHF signal at the receiver. Available methods are: o o Subtraction of the own DSB-AM signal if the VHF channel for DSB-AM voice communication lies within the B-VHF transmission bandwidth. Since this signal is available at the B-VHF aircraft, it is possible to subtract it at the B-VHF frontend before A/D conversion. Subtraction of the carrier signal of strong DSB-AM interferers. Since the carrier signal of a DSB-AM signal can be easily estimated, it can be subtracted at the B-VHF frontend before A/D conversion. o Notch filtering before A/D conversion at VHF channels with strong interferers. Note, these VHF channels are not used for the B-VHF transmission. Thus, notch filtering does not influence the B-VHF signal. Digital time domain methods: After A/D conversion the DSB-AM interference from these VHF channels within the B-VHF transmission bandwidth which are used by the B-VHF system, i.e. VHF channels which might only obtain so-called weak DSB-AM interferers, is suppressed applying the following time domain methods: o o Windowing of the received signal in order to reduce the leakage effect. This method achieves that the interference power stays concentrated and only affects a few sub-carriers. Digital adaptive time domain equalizer. Digital frequency domain methods: After A/D conversion and transformation of the received signal into the frequency domain the DSB-AM interference is further suppressed using digital signal processing in the frequency domain. As for the digital time domain methods, these methods are applied for the DSB-AM interference from these VHF channels within the B-VHF transmission bandwidth which are used by the B-VHF system. The most promising method is: o Subtraction of the interference contribution from DSB-AM interferers on each sub-carrier. Using some unmodulated sub-carriers, the interference on each sub-carrier can be estimated and removed in digital frequency domain. As shown above, several countermeasures are available to significantly reduce the narrowband interference from the legacy VHF systems towards the B-VHF system. Copyright B-VHF Consortium Page: 9-12

80 Therefore, we expect that B-VHF is able to cope with the narrowband interference coming from the legacy VHF systems. As main result of the B-VHF capacity analysis, the following conclusions are given: The available capacity in the VHF band for introduction of the B-VHF system is in a worst-case scenario well above 25% even for large cells in areas with extremely high aircraft density. Thus, there is enough B-VHF capacity available in the VHF band. Interference from the B-VHF system towards the legacy VHF systems is avoided due to an appropriate B-VHF system design. Especially, the maximum allowed B-VHF transmit power is chosen in order not to disturb the legacy VHF systems. The maximum allowed B-VHF transmit power still guarantees a very good SNR for B-VHF transmission and with that excellent performance as long as no narrowband interference from the legacy VHF systems is present. Narrowband interference from the legacy VHF systems towards the B-VHF system can be quite large resulting in low SIR values. However, as described above an appropriate system design using spreading and coding together with interference suppression at the B-VHF receiver reduces the influence of the narrowband interference significantly. Thus, we expect that the B-VHF system is able to work properly under these narrowband interference conditions END OF SECTION Copyright B-VHF Consortium Page: 9-13

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82 10. References Nr. Reference ID Reference 1 [AMCP8-WP51] AMCP eighth meeting, Montreal, 4-13 Feb. 2003/ WP/51, VDL Frequency Assignment Planning Criteria 2 [SPG/CP0108] DIS/COM/SPG/CP0108 Radio Characteristics of Aviation Radio Systems, Step 1, Ver. 2.0, [AMCP8-WP44] AMCP eighth meeting, Montreal, 4-13 Feb. 2003/ WP/44, PROGRESS OF THE VDL SUB BAND IMPLEMENTATION IN EUROPE 4 [GET MET] GET MET 2004, Brochure of UK CAA Met Office, 5 [CEPT ARC] CEPT/ERC- THE EUROPEAN TABLE OF FREQUENCY ALLOCATIONS AND UTILISATIONS COVERING THE FREQUENCY RANGE 9 khz TO 275 GHz, Lisboa January 2002 Revised Dublin [EUR_FM_man] ICAO EUROPEAN AND NORTH ATLANTIC OFFICE EUR FREQUENCY MANAGEMENT MANUAL for Aeronautical Mobile and Aeronautical Radio Navigation Services, EUR Doc 011, Edition 2003, September 2003 (unofficial version) 7 [RTCA-DO224A] RTCA/DO224A- MASPs for Advanced VHF Digital Data Communications Including Compatibility With Digital Voice Techniques, Sept. 13, [ETSI_VDL4] ETSI EN V1.1.1 ( ), Electromagnetic compatibility and Radio spectrum Matters (ERM); VHF air-ground Data Link (VDL) Mode 4 radio equipment; Technical characteristics and methods of measurement for ground-based equipment; Part 1: General description and physical layer 9 [ARINC_618] AIR/GROUND CHARACTER-ORIENTED PROTOCOL SPECIFICATION ARINC SPECIFICATION 618-5, PUBLISHED: AUGUST 31, [DO-186A] RTCA/DO-186A, Minimum Operational Performance Standards for Airborne Radio Communications Equipment Operating Within The Radio Frequency Range 117, ,000 MHz, October 20, [VOCALISE_2] Etude Vocalise : Analyse générale Trafic CRNA / France 2000, Une analyse du canal vocal pilotes contrôleurs dans la perspective d un environnement data-link, CENA/ICS/R02-002, version 1.0, 07/03/02 12 [WGB16/WP19] AERONAUTICAL COMMUNICATIONS PANEL (ACP) Working Group B, Tokyo, 28 th January to 6 February 2004, ACP/WG-B/WP_19, Assessment of VDL Mode-2 airborne co-site interference in Link2000+ framework 13 [ANNEX10] ICAO Annex 10 Volume I 14 [NERL_GS] Data base of En-route and TMA ground stations in UK, NERL, Frequencies and Radio Stations.mdb, [EUROC_VHF] EUROCONTROL Data base of European VHF frequency allocations, BP17_COM2DB.mdb 16 [CLIMAX_TECH] EATMP/ Feasibility and benefit analysis of CLIMAX operations on a VHF 8.33 khz channelisation, WP 2 Technical feasibility, Deliverables D2.a and D2.b, Ed. 1.0 Copyright B-VHF Consortium Page: 10-1

83 Nr. Reference ID Reference 17 [DFS_VDL4] Report on test procedures and measurement results for the development of frequency planning criteria for VDL Mode 4, Author: Dr. Armin Schlereth, DFS, Date: 5 th September [Aero_Chan] Aeronautical Channel Modeling from Erik Haas, IEEE Transactions on Vehicular Technology, Vol. 51, No. 2, Mar 2002, pp [ETSI VDL2] ETSI EN V1.1.1 ( ), European Standard (Telecommunications series) Electromagnetic compatibility and Radio spectrum Matters (ERM); VHF air-ground Digital Link (VDL) Mode 2; Technical characteristics and methods of measurement for groundbased equipment; Part 1: Physical layer 20 [VDL2_AIR] EUROCAE/ MINIMUM OPERATIONAL PERFORMANCE SPECIFICATION FOR AN AIRBORNE VDL MODE-2 SYSTEM OPERATING IN THE FREQUENCY RANGE MHz, ED-92A, October [VDL4_AIR] EUROCAE/ INTERIM MINIMUM OPERATIONAL PERFORMANCE SPECIFICATION FOR VDL MODE 4 AIRCRAFT TRANSCEIVER, PART 1: CORE REQUIREMENTS, DRAFT version GH, 23rd January 2004, ED- 108A 22 [B-VHF D12] B-VHF Report D12 VHF Channel Occupancy Measurements, ISSUE/Rev 1.0, [AMCP/WGB11] AMCP meeting, Montreal, / WP/3, Interference tests linked to VDL Mode 2 integration on Airbus aircraft 24 [B-VHF D14] B-VHF Report D14 Software Implementation of the Interference Model (to be issued end of April 2005) 25 [B-VHF D18] B-VHF Report D18 Physical Layer Design for Forward and Reverse Link, to be issued December END OF SECTION Copyright B-VHF Consortium Page: 10-2

84 11. Abbreviations 4DTN 4G A/A A/G A3E ACARE ACARS ACC ADS-B AEEC AFIS AFTM AIP AIS AMCP AMS AMSS ANS AoA AOC AOC APC APP ARINC ASAS ATC ATCC ATIS ATM ATN ATS ATSP ATSU BCST 4 Dimensional Trajectory Negotiation Fourth Generation Air-Air Air-Ground Double sideband modulation Advisory Council for ATM Research in Europe Aircraft Communications Addressing and Reporting System Area Control Centre Automatic Dependent Surveillance - Broadcast Airlines Electronic Engineering Committee Aerodrome Flight Information Service Air Traffic Flow Management Aeronautical Information Publication Aircraft Information Service Aeronautical Mobile Communications Panel Aeronautical Mobile Service Aeronautical Mobile Satellite Services Air Navigation Services ACARS over AVLC Airline Operations Centre Airline Operational Communications Aeronautical Passenger Communications Approach Aeronautical Radio INCorporated Airborne Separation Assurance System Air Traffic Control Air Traffic Control Centre Automatic Terminal Information Service Air Traffic Management Aeronautical Telecommunications Network Air Traffic Services Air Traffic Service Provider Air Traffic Service Unit Broadcast Copyright B-VHF Consortium Page: 11-1

85 BER B-VHF CAA CDMA CFMU CMU CNS COM CoS CPDLC CSMA CTA CTR D/U D8PSK Dx DAP dbc dbm DCL DDM DEP D-FIS DLL DOC DQPSK DSB DSB-AM EATMS EC ECAC EIRP ES EUROCAE fc FCH Bit Error Rate Broadband Very High Frequency Civil Aviation Authority Code Division Multiple Access Central Flow Management Unit Communications Management Unit Communication, Navigation and Surveillance Communications Class of Service Controller Pilot Data Link Communication Carrier Sense Multiple Access Control Area Control Zone Signal Ratio between Desired and Undesired Signals Differentially encoded 8-Phase Shift Keying B-VHF Project Deliverable x Downlink of Aircraft Parameters db relative to carrier db relative to milli Watt Departure CLearance Difference in Depth of Modulation Departure Data Link Flight Information Service Data Link Logon (service) Designated Operational Coverage Differential Quadrature Phase Shift Keying Dual Side Band Dual Side Band Amplitude Modulation European Air Traffic Management System European Commission European Civil Aviation Conference Equivalent Isotropically Radiated Power End System EURopean Organisation for Civil Aviation Equipment Carrier frequency Fast Channel Copyright B-VHF Consortium Page: 11-2

86 FEC FIR FIS FIS-B FL FL FMG FMP FP6 GBAS GFSK GICB GMSK GND GNSS GS HF HZ IATA ICAO IFPS IFR ILS ITU kbps LLC MACONDO MC MC-CDMA MCST MSK N/A NATS NAV NAVSIM Forward Error Coding Flight Information Region Flight Information Service Flight Information Service - Broadcast Flight Level Forward Link Frequency Management Group Flight Management Position Sixth Framework Programme Ground-based Augmentation System Gaussian Frequency Shift Keying Ground-Initiated Control protocol B Gaussian Minimum Shift Keying Ground Global Navigation Satellite System Ground Station High Frequency Homogenous Zone International Air Transport Association International Civil Aviation Organisation Initial Flight Plan Processing System Instrument Flight Rules Instrument Landing System International Telecommunications Union Kilobit per second Logical Link Control Nickname for the EUROCONTROL study - Operating Concept of the Mobile Aviation Communication Infrastructure Supporting ATM beyond 2015 Multi-Carrier Multi-Carrier Code Division Multiple Access Multicast Minimum Shift Keying Not Applicable National Air Traffic Services Navigation ATM/ATC & CNS simulation tool Copyright B-VHF Consortium Page: 11-3

87 NexSAT nm OC ODIAC OFDM OPC OSI P2P PHY PoA ppm QoS R/T RCP RCTP RF RGS RSS RT RTCA RVSM RX SAP SAR SATCOM ScOACC SIR SNR SQU STAR STDMA SW TBD TC TDMA TMA EUROCONTROL s name for new generation satellite system Nautical mile Operational Concept Operational Development of Initial Air / ground Data Communications Orthogonal Frequency Division Multiplexing Operational Control Communications Open System Interconnect Point to Point Physical Layer (OSI model) Plain old ACARS Parts per million Quality of Service Radio Telephony Required Communications Performance Required Communications Technical Performance Radio Frequency Remote Ground Station Received Signal Strength Radio Telephony Radio Technical Commission for Aeronautics Reduced Vertical Separation Minima Receiver System Access Parameters (service) Search and Rescue Satellite Communications Scottish and Oceanic Area Control Ce Signal to Interference Ratio Signal to Noise Ratio Squelch (signal) Standard Instrument Arrival Self-organising Time Division Multiple Access Software To Be Defined Terminal Control Time Division Multiple Access Terminal Manoeuvring Area Copyright B-VHF Consortium Page: 11-4

88 TOD Top Of Descent TP4 Transport Protocol 4 TWR ToWeR TX Transmitter UAC Upper Area Control UAR Upper Air Routes UIR Upper Flight Information Region UK United Kingdom ULA Upper Layer UTC Universal Time Co-ordinated VDB VHF Data Broadcast VDL VHF Digital Link VDL2 VHF Digital Link Mode 2 VDL3 VHF Digital Link Mode 3 VDL4 VHF Digital Link Mode 4 VDR VHF Data link Radio VHF Very High Frequency VOR VHF Omni-directional Range WAN Wide Area Network W-CDMA Wideband CDMA WGS84 World Geodetic System 1984 WP Work Package END OF SECTION Copyright B-VHF Consortium Page: 11-5

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90 12. Appendix A Link Budget Analysis The purpose of this section is twofold. First, link budget analysis is a key element of the system design procedure in order to assess the power levels, sensitivity, and coverage area of each transmitting element in all relevant scenarios. On the other hand, the potential interference from the B-VHF system to existing VHF systems and vice versa should be determined. The interference is strongly influenced by the maximum transmission power, the cell size and the user data. The tolerable power and the power distribution of such interference, together with the frequency plan of the B-VHF radio network will influence the transition concept. The link budget analysis gives a first indication about potential restrictions for achieving a reasonable system capacity of an overlay concept. The discussion below describes the link budget for an ATC voice application, and clarifies which parameters within the system can be adapted for different scenarios. Designing radio communications systems, that transmits over line-of-sight or similar channels, the transmitted power, system capacity, spreading factor, and the signal-tonoise ratio (SNR) required to achieve a given level of performance at some desired user data rate, are the key parameters, which gives a first indication for potential risk and quality degradations. By evaluating the system performance, the most important parameter is the SNR, because the system design concentrates on the ability to detect the signal, with an acceptable error probability, in the presence of the noise. In a case where the signal is a modulated carrier wave, as in a radio, the average carrier power-to-noise ratio (C/N) is often used. The link budget details the apportionment of transmission and reception sources, noise sources and signal attenuators. As some of the budget parameters are statistical like the attenuation of the propagation path due to meteorological event and multi-path propagation, the link budget is always only a estimation for the system performance. To get a sufficient power level in the reception, a required transmission power is calculated in the link budget, when, e.g., the transmission distance, modulation method, desired bit-error rate (BER) and transfer rate (bit/s) are known. On the other hand with a link budget the longest possible transfer distance, the potential interference power for other systems or some other system parameter can be calculated when the required Eb/N 0 and the characteristics of the radio link are known System parameter description The following section provides a description of the link budget items. Descriptions apply to both forward and reverse link unless explicitly stated otherwise. For the forward link the ground station is the transmitter and the aircraft is the receiver. For the reverse link the aircraft is the transmitter and the base station the receiver.! Average transmitter power per traffic channel (dbm) The average transmitter power per traffic channel is defined as the mean of the total transmitted power over an entire transmission cycle with maximum transmitted power when transmitting.! Maximum transmitter power per traffic channel (dbm) Maximum transmitter power per traffic channel is defined as the total power at the transmitter output for a single traffic channel. A traffic channel is defined as a communication path between an aircraft and a ground station used for user and Copyright B-VHF Consortium Page: 12-1

91 signalling traffic. The term traffic channel denotes a forward and reverse traffic channel pair.! Maximum total transmitter power (dbm) Maximum total transmit power is the aggregate maximum transmit power of all channels. In a multi-carrier system, the transmit power is the total power of all carriers transmitted simultaneously and intended to be received by one receiver simultaneously.! Cable, connector, and combiner losses (transmitter) (db) These are the combined losses of all transmission system components between the transmitter output and the antenna input (all losses in positive db values). This value is fixed in the link budget tables.! Transmitter antenna gain (dbi) Transmitter antenna gain is the maximum gain of the transmitter antenna (specified as db relative to an isotropic radiator). This value is fixed in the link budget tables.! Transmitter EIRP (dbm) This is the sum of the total transmitter power (dbm), transmission system losses (- db), and the transmitter antenna gain (dbi).! Receiver antenna gain (dbi) Receiver antenna gain is the maximum gain of the receiver antenna in the horizontal plane (specified as db relative to an isotropic radiator).! Cable, connector, and splitter losses RL (receiver) (db) These are the combined losses of all transmission system components between the receiving antenna output and the receiver input (all losses in positive db values). This value is fixed in the link budget tables.! Receiver noise figure FR (db) Receiver noise figure is the noise figure of the receiving system referenced to the receiver input. This value is fixed in the link budget tables. To achieve a fair performance comparison, different technologies should be tailored to similar environmental interference conditions and should have identical receiver noise figure specifications. Thus, for evaluation purposes it is required that all technology proposals use the same receiver noise figure (NF) specs: 7 db for the aircraft and 5 db for the ground station.! External noise figure FE (db) The external noise is a combination of atmospheric noise, galactic noise, and manmade noise, with the latter predominating in areas of human activity (i.e., almost everywhere).! Thermal noise density N0 (dbm/hz) Thermal noise density, N0, is defined as the noise power per Hertz at the receiver input.! Receiver interference density I0 (mw/hz) Receiver interference density is the interference power per Hertz at the receiver front end. This is the in-band interference power divided by the system bandwidth. The in-band interference power consists of co-channel interference, adjacent channel interference and inter-system interference from other systems within the used bandwidth. Thus, the receiver and transmitter spectrum masks must be taken into account. Note, this term is expressed in linear units. Receiver interference Copyright B-VHF Consortium Page: 12-2

92 density I0 for the forward link is the interference power per Hertz at the aircraft receiver located at the edge of coverage, in an en-route, approach or airport sector. Since the inter-system interference is not known until now, this value is not considered in the tables.! Total effective noise density N0 effective (dbm/hz) Since the receiver interference density is not considered in this link budget analysis, only this term is used and not the total effective noise plus interference density. The total effective noise density is the arithmetic sum of the receiver noise figure and the external noise figure minus receiver losses (R L ) and the logarithmic sum with the receiver noise density. FR FE-RL N0effective = 10log( ) + N0! Information rate (10 log Rb) (db(hz)) Information rate is the channel bit rate in (db(hz)); the choice of Rb must be consistent with the Eb assumptions.! Required Eb/(N0) (db) The ratio between the received energy per information bit to the total effective noise power density needed to satisfy the quality objectives specified for each service class in order to meet the BER taking channel model, modulation scheme and coding into account. Diversity gains included in the Eb/N0 requirement should be specified here to avoid double counting. The translation of the threshold error performance to Eb/N0 performance depends on the particular multi-path conditions assumed. The required carrier power-to-noise ratio in the ideal case can be calculated from the equation where fb is the transfer bit rate and Bn the noise bandwidth. C N = E N! Receiver sensitivity (dbm) This is the signal level needed at the receiver input that just satisfies the required Eb/N0. The theoretical receiver sensitivity is expected to be different for each technology applied. For fair comparison, it is required to uniquely specify the receiver sensitivity, e.g., for a raw data bit error rate (BER) of 0.1%. b 0 The receiver sensitivity (in dbm) shall be calculated using the following formula: Sensitivity = ( dbm) + NF (in db) + 10 log (channel-bw in Hz) + C/N min for 0.1% BER).! Explicit diversity gain (db) This is the effective gain achieved using diversity techniques. It should be assumed that the correlation coefficient is zero between received paths. Note that the diversity gain should not be double counted. For example, if the diversity gain is included in the Eb/N0 specification, it should not be included here.! Other gain (db) An additional gain may be achieved due to future technologies. For instance, space f B b n Copyright B-VHF Consortium Page: 12-3

93 diversity multiple access (SDMA) may provide an excess antenna gain. Assumptions made to derive this gain must be given by the proponent.! Fade margin (db) The Rice and Rayleigh fade margins are defined at the cell boundary for isolated cells. This is the margin required to provide a specified coverage availability over the individual cells. For this link budget analysis a minimum of 95% reliability at the cell boundary on the airport (Rayleigh channel) and a minimum of 99% reliability at en-route and approach sectors (Rice channel with K~15dB) is assumed.! Maximum path loss (db) This is the maximum loss that permits minimum performance at the sector/cell boundary: The used formula is founded in Section Required carrier power-to-noise ratio The worst acceptable BER for data transmission gives the requirements for the signal-tonoise ratio. The error performance depends on the modulation in use and the error performance. Thus to obtain, e.g., the BER of 10-3, the symbol energy-to-noise spectral E b density rate must be at least 7dB for QPSK on the AWGN channel (Additive White N0 Gaussian Noise). In Figure 12-1 different types of modulation techniques and their error probabilities versus E b N 0 at an AWGN channel are illustrated. Figure 12-1: BER as a function of Eb/N0 Copyright B-VHF Consortium Page: 12-4

94 Figure 12-2: BER vs Eb/N0 for QPSK Modulation with different coding rates Although the aeronautical channel is not an AWGN channel the curves of Figure 12-1 and Figure 12-2 above can be used for the link budget analysis, at least for en-route and TMA sectors, as described in the paper [Aero_Chan] the aeronautical channel for en-route and approach is modelled as a Rice channel with a Rice factor of 15 db (see the following values): Parking scenario: Rice factor K: - db Taxi scenario: Rice factor K: 6.9dB Arrival scenario: Rice factor K: 15 db En-route scenario: Rice factor K: 15 db By a fading channel with a Rice factor of 15 db the required energy-to-noise spectral density is similar to an AWGN channel. The degradation is in the range of 1-2 db. Copyright B-VHF Consortium Page: 12-5