Survey on the Future Aeronautical Communication System and Its Development for Continental Communications
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paper_title: B-VHF – A MULTI-CARRIER BROADBAND COMMUNICATIONS CONCEPT FOR AIR TRAFFIC MANAGEMENT IN THE VHF BAND

paper_content:

In this paper we describe an European initiative aiming to establish a broadband Very High Frequency (VHF) aeronautical communications system based on a multi-carrier technology and demonstrate its benefits to the aeronautical community, together with its technological fundamentals. The European research project B-VHF (“Broadband VHF Aeronautical Communications System based on Multi-Carrier Techniques”) is funded by the European Commission within the 6 Framework Program and has started in January 2004. The project deals with the investigation, design, and evaluation of a broadband overlay communications system for Air Traffic Control (ATC) and Air Traffic Management (ATM) communications in the VHF band. The proposed transmission technique, which permits the parallel operation with the current AM system, is called Multi-Carrier Code-Division Multiple-Access (MC-CDMA.
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paper_title: B-VHF - an overlay system concept for future ATC communications in the VHF band

paper_content:

In this paper, the European research project B-VHF is introduced which is funded by the European Commission and has started in January 2004. The main goal of the B-VHF project is to prove that it is feasible to establish a multi-carrier based overlay system for future air traffic control (ATC) communications in the very high frequency (VHF) band without causing interference to the legacy VHF systems. Note this overlay system concept enables in-band transition from the current to a future ATC communications system and, thus, allows future ATC communications to stay in the advantageous and protected VHF band. The focus in this paper is on the technical approach for realizing the overlay concept. Thus, the technology behind B-VHF are described in detail and how it is applied for realizing an overlay system in the VHF band.
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paper_title: B-VHF – A MULTI-CARRIER BROADBAND COMMUNICATIONS CONCEPT FOR AIR TRAFFIC MANAGEMENT IN THE VHF BAND

paper_content:

In this paper we describe an European initiative aiming to establish a broadband Very High Frequency (VHF) aeronautical communications system based on a multi-carrier technology and demonstrate its benefits to the aeronautical community, together with its technological fundamentals. The European research project B-VHF (“Broadband VHF Aeronautical Communications System based on Multi-Carrier Techniques”) is funded by the European Commission within the 6 Framework Program and has started in January 2004. The project deals with the investigation, design, and evaluation of a broadband overlay communications system for Air Traffic Control (ATC) and Air Traffic Management (ATM) communications in the VHF band. The proposed transmission technique, which permits the parallel operation with the current AM system, is called Multi-Carrier Code-Division Multiple-Access (MC-CDMA.
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paper_title: B-VHF - an overlay system concept for future ATC communications in the VHF band

paper_content:

In this paper, the European research project B-VHF is introduced which is funded by the European Commission and has started in January 2004. The main goal of the B-VHF project is to prove that it is feasible to establish a multi-carrier based overlay system for future air traffic control (ATC) communications in the very high frequency (VHF) band without causing interference to the legacy VHF systems. Note this overlay system concept enables in-band transition from the current to a future ATC communications system and, thus, allows future ATC communications to stay in the advantageous and protected VHF band. The focus in this paper is on the technical approach for realizing the overlay concept. Thus, the technology behind B-VHF are described in detail and how it is applied for realizing an overlay system in the VHF band.
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paper_title: Future communication study technology investigation conclusions and recommendations

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The aim of the work was the investigation of potential communications technologies to support the long-term aeronautical mobile air-ground data link communication requirements considering terrestrial and satellite based infrastructure. This paper presents the assessment of the final five candidate technologies, and also provides an overview of the entire technology assessment process, including final findings and recommendations of the future communication study (FCS) technology investigation and assessment.
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paper_title: Analysis of L-Band Digital Aeronautical Communication Systems: L-DACS1 and L-DACS2

paper_content:

New air-to-ground wireless datalinks are needed to supplement existing civil aviation technologies. The 960 – 1164 MHz part of the IEEE L band has been identified as a candidate spectrum. EUROCONTROL — the European organization for the Safety of Air Navigation, has funded two parallel projects and developed two proposals called L-DACS1 and L-DACS2. Although, there is a significant amount of literature available on each of the two technologies from the two teams that designed the respective proposals, there is very little independent comparison of the two proposals. The goal of this paper is to provide this comparison. We compare the two proposals in terms of their scalability, spectral efficiency, and interference resistance. Both the technologies have to co-exist with several other aeronautical technologies that use the same L-band. 12
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paper_title: L-DACS1 laboratory demonstrator development and compatibility measurement set-up

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In this paper, the L-DACS1 physical layer laboratory demonstrator development is described which has been recently carried out by the German Aerospace Center (DLR). The main goal of the lab demonstrator is to perform first compatibility measurements between L-DACS1 and legacy L-band systems where interference from L-DACS1 towards the legacy systems as well as interference from the legacy systems onto the L-DACS1 receiver is considered. In addition to the demonstrator description, results from functional tests of the lab demonstrator as well as the measurement scenarios foreseen for compatibility testing are presented. The compatibility measurements will take place at the labs of the Deutsche Flugsicherung GmbH (DFS) — the German ATC provider — in fall this year.
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paper_title: L-DACS1 physical layer laboratory demonstrator

paper_content:

In this paper, an L-DACS1 physical layer laboratory demonstrator is presented which has been implemented recently in FPGA technology by the German Aerospace Center (DLR). The main goal of this lab demonstrator is to perform first compatibility measurements between L-DACS1 and legacy L-band systems where interference from L-DACS1 towards the legacy systems as well as interference from the legacy systems onto the L-DACS1 receiver is considered. The lab demonstrator is already implemented up to the first intermediate frequency at 10.7 MHz. The radio frontend for up-/down-conversion to/from the L-band is scheduled to be delivered in May this year. First compatibility tests are planned to take place in the labs of the German ATC authority DFS this summer. Using real hardware equipment, these tests will give valuable insight into the L-band coexistence issue and possible deployment scenarios.
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paper_title: Effect of the Aeronautical L-DACS2 Radio-Frequency Signals on the DME System Performance

paper_content:

In this paper, we consider the Radio-Frequency Compatibility (RFC) of a candidate system for the future aeronautical communication infrastructure. This infrastructure is being developed within the International Civil Aviation Organization since 2004, to accommodate the air traffic load and improve the aerial security. The system presented in this paper is one of the two preselected proposals for the L-band Digital Aeronautical Communication System (L-DACS), which will be responsible for the continental communications. This proposed candidate is named L-DACS2 and is foreseen to use part of the L-band spectrum (960 to 1164 MHz) allocated to the Aeronautical Mobile Service reserved for communications relating to safety and regularity of flight. Despite its potentially large spectrum, the L-band is a challenging environment for aeronautical communications because of the channel propagation characteristics and the dense spectral occupation by a large number of aeronautical systems. On the other hand, the RFC characterizes the electromagnetic compatibility between two radio systems and determines if they can coexist in the same electromagnetic environment. For this reason, the RFC is one of the main issues for L-DACS deployment and if it is not satisfied, the flight safety could be endangered. Hence, we propose to study in this paper the impact of the L-DACS on the Distance Measuring Equipment (DME), which is a very important equipment that has been using this band for decades. According to recent studies performed in the frequency domain , that is assuming continuous transmissions and no time domain variations, the achieved RFC level seems insufficient. The main objective of this work is to analyze the RFC between L-DACS2 and DME taking into account the time domain aspects of both systems. The idea is to verify and quantify the impact of the radio- frequency signals generated by a L-DACS2 interferer on the performance of a DME victim receiver. The study is performed for the co-site case (\emph{i.e.} when both equipments are onboard of the same airplane), which is the most critical interference scenario due to the proximity of both systems. The results are obtained through computer simulations as well as laboratory measurements. They present the DME performance degradation for some values of the Signal to Interference Ratio, assuming a constant DME signal level and different L-DACS2 interference powers.
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paper_title: Radioelectric compatibility of the future aeronautical communication system

paper_content:

The aeronautical community has recently decided to develop a new digital aeronautical communication system, named L-DACS, in order to fulfill the new air traffic requirements. This system, which will operate in the L frequency band (960 to 1164 MHz), would be internationally deployed from 2020. Many technologies were considered for this new aeronautical system but only two among them were preselected by the International Civil Aviation Organization (ICAO): candidate one, named L-DACS1, is based on a FDD-OFDM technology and candidate two, named L-DACS2, is based on a TDD-GMSK technology. One of the most important issues for both candidates is the electromagnetic compatibility (EMC) with the legacy systems operating in the same band or/and in adjacent bands. Different scenarios have to be evaluated due to the fact that these systems will be implanted either in the airplanes (on board) or in ground stations. In this paper, we propose to evaluate the air-air scenario, where we focus on the signals generated by onboard L-DACS transmitters on onboard victim receivers, taking into account the L-DACS antenna radiation pattern and the frequency mask. The study emphasizes that the interference phenomenon can be one of the main limitations for the L-DACS development.
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paper_title: Interference analysis for the future aeronautical communication system

paper_content:

General and commercial aviation authorities have been using amplitude modulation communication systems for more than 70 years. Due to the great increase of air traffic during the last years, the VHF band tends towards saturation, whereas the aeronautical community faces new requirements: data rate, spectral efficiency and network capacity (maximum number of aircrafts simultaneously connected). Recently, the development of a new digital aeronautical communication system, named L-DACS, was proposed. This system will operate in the L band part allocated to aeronautics. There were many proposals but only two candidates have been pre-selected by the ITU and ICAO for this future communication system: L-DACS1 and L-DACS2. The deployment of this new system is expected to start after 2020. Among other issues, one important aspect is the impact of L-DACS on legacy systems. Actually, there are many onboard systems operating in L band, and any disfunction can put in danger the flight safety. This paper studies the maximum interference level generated by the two L-DACS candidates on a generic onboard receiver. Taking into account the antenna radiation pattern and the specific transmission mask of both candidates, the study determines the worst interference level and the corresponding spatial positions of the aircrafts around the receiver. The results show that the interference level can be determined by considering the several nearest aircrafts to the victim.
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paper_title: Receiver optimization for L-DACS1

paper_content:

L-DACS1 is the broadband candidate technology for the future L-band Digital Aeronautical Communications System (L-DACS). The flexible design of L-DACS1 allows the deployment as an inlay system in the spectral gaps between two adjacent channels used by the Distance Measuring Equipment (DME) as well as the non-inlay deployment in unused parts of the L-band. In this paper, the synchronization procedure in L-DACS1, when deploying it as inlay system is presented. It will be investigated how the synchronization suffers from interference in the L-band. In addition, interference mitigation techniques are briefly described and their influence onto the synchronization is examined. Finally, the performance of an appropriate combination of interference mitigation and robust synchronization is presented, showing that even under severe interference conditions, a reliable synchronization can be accomplished, hence confirming the feasibility of the inlay concept.
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paper_title: Suppression of Mutual Interference in OFDM Based Overlay Systems

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A promising appraoch for overcoming spectrum scarcity are overlay systems that share a frequency band with already existing licensed systems by using the spectral gaps left by the licensed systems. Due to its spectral efficiency and flexibility orthogonal frequency-division multiplexing (OFDM) is an appropriate modulation technique for overlay systems. To enable a successful co-existence, techniques for suppressing mutual interferences between the overlay and the licensed system are proposed.
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paper_title: Interference mitigation for broadband L-DACS

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One deployment option for the future broadband L-band digital aeronautical communications system (L-DACS) is operating as an inlay system between two adjacent channels of the distance measuring equipment (DME) system. Investigations for the broadband aeronautical multi-carrier communications (B-AMC) [1] system, one candidate for the broadband L-DACS, have shown that interference originating from DME systems operating in adjacent channels has a strong impact on the B-AMC system. To enable the utilization of spectral gaps between two adjacent DME channels, two efficient methods for mitigating the impact of interference are proposed and investigated for the B-AMC system, namely pulse blanking and erasure based decoding. Simulations show that the impact of DME interference onto the L-DACS can be reduced considerably by choosing an appropriate coding scheme to make the transmit signal robust against interference. The impact of interference is mitigated by means of the proposed methods, resulting in a performance close to the performance in the interference-free case.
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paper_title: Compensation of the Impact of Interference Mitigation by Pulse Blanking in OFDM Systems

paper_content:

When pulsed interference is mitigated by means of pulse blanking, interference is reduced significantly. However, at the same time certain fractions of the useful orthogonal frequency-division multiplexing (OFDM) signal are erased. Consequently, only moderate improvements are achieved with pulse blanking. When representing the pulse blanking operation as multiplication with a rectangular window exhibiting notches at the positions where blanks are inserted, it becomes obvious, that pulse blanking mainly leads to inter-carrier interference (ICI). In this paper, the compensation of the impact of pulse blanking is proposed by reconstructing and subtracting ICI. The required shape of the subcarrier spectra is derived from the pulse blanking window. For an estimation of the transmitted data symbols and the channel coefficients of each subcarrier an iterative receiver structure is proposed. Simulation results at hand of a realistic interference scenario show that with perfect channel estimation and known data symbols the impact of pulse blanking can be reduced to a small loss in signal-to-noise ratio resulting from the energy loss due to erasing a certain fraction of the OFDM signal. With real channel estimation and estimated data symbols, the ideal case with perfect channel estimation and known data symbols is approached by 1.2 dB after only three iterations.
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paper_title: L-DACS1 physical layer laboratory demonstrator

paper_content:

In this paper, an L-DACS1 physical layer laboratory demonstrator is presented which has been implemented recently in FPGA technology by the German Aerospace Center (DLR). The main goal of this lab demonstrator is to perform first compatibility measurements between L-DACS1 and legacy L-band systems where interference from L-DACS1 towards the legacy systems as well as interference from the legacy systems onto the L-DACS1 receiver is considered. The lab demonstrator is already implemented up to the first intermediate frequency at 10.7 MHz. The radio frontend for up-/down-conversion to/from the L-band is scheduled to be delivered in May this year. First compatibility tests are planned to take place in the labs of the German ATC authority DFS this summer. Using real hardware equipment, these tests will give valuable insight into the L-band coexistence issue and possible deployment scenarios.
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Title: Survey on the Future Aeronautical Communication System and Its Development for Continental Communications

Section 1: Introduction
Description 1: Introduce the need for improving aeronautical communication systems and how the ICAO has recognized this need along with the current systems' limitations.

Section 2: Why a New System for Aeronautical Mobile Communications?
Description 2: Discuss the limitations of current VHF systems used for civil air traffic control and the necessity for a new communication system to meet future traffic and data requirements.

Section 3: Future Communication Infrastructure Development Activities from 2004 to 2009
Description 3: Outline the joint development activities between Europe and the U.S. to support ICAO discussions, including the phases of the Future Communication Infrastructure (FCI) development.

Section 4: Overview
Description 4: Provide an overview of FCI's multi-phase development process and technology assessment criteria used from 2004 to 2007.

Section 5: Current Status: L-DACS Investigations
Description 5: Detail the focus and progress of L-DACS development, including technology assessments, identification, and preselection of L-DACS1 and L-DACS2 systems.

Section 6: Two L-Band Digital Aeronautical Communication System Candidate Systems
Description 6: Describe the main characteristics of the two L-DACS candidates, L-DACS1 and L-DACS2, along with their physical and medium access control layer differences.

Section 7: Before the Final L-Band Digital Aeronautical Communication System Choice
Description 7: Outline the ongoing studies and tasks necessary to support the final decision on L-DACS technology, including interference mitigation and performance evaluation.

Section 8: L-Band Digital Aeronautical Communication System Challenges
Description 8: Discuss the various challenges that L-DACS must overcome prior to deployment, including standardization, EMC conformity, radio resource optimization, and coping with air traffic growth.

Section 9: Conclusion
Description 9: Summarize the survey's findings on the necessity and development of the future aeronautical communication system, with an emphasis on L-DACS and its potential to meet future aviation needs.