The LDACS1 Physical Layer Design

The legacy DSB-AM (Double Sideband Amplitude Modulation) system used for todayâs voice communication in the VHF-band is far away of meeting the demands of increasing air traffic and associated communication load. The introduction of VDL (VHF Digital Link) Mode 2 in Europe has already unfolded the paradigm shift from voice to data communication. Legacy systems, such as DSB-AM and VDL Mode 2 are expected to continue to be used in the future. However, they have to be supplemented in the near future by a new data link technology mainly for two reasons. First, only additional communication capacity can solve the frequency congestion and accommodate the traffic growth expected within the next 10-20 years in all parts of European airspace (ICAO-WGC, 2006). Second, the modernization of the Air Traffic Management (ATM) system as performed according to the SESAR (http://www.sesarju.eu/) and NextGen (http://www.faa.gov/nextgen/) programs in Europe and the US, respectively, heavily relies on powerful data link communications which VDL Mode 2 is unable to support. Based on the conclusions of the future communications study (Budinger, 2011), the ICAO Working Group of the Whole (ICAO-WGW, 2008) has foreseen a new technology operating in the L-band as the main terrestrial component of the Future Communication Infrastructure (FCI) (Fistas, 2011) for all phases of flight. Hence, such L-band technology shall meet the future ATM needs in the en-route and the Terminal Manoeuvring Area (TMA) flight domains as well as within airports. The latter application area will be supplemented by the AeroMACS technology at many large airports (Budinger, 2011). A final choice of technology for the L-band has not been made yet. Within the future communications study, various candidate technologies were considered and evaluated. However, it was found that none of the considered technologies could be fully recommended before the spectrum compatibility between the proposed systems and the legacy systems has been proven. This will require the development of prototypes for testing in a real environment against operational legacy equipment. The future communications study has identified two technology options for the L-band Digital Aeronautical Communication System (LDACS) as the most promising candidates for meeting the requirements on a future aeronautical data link. The first option, named LDACS1, is a Frequency-Division Duplex (FDD) configuration utilizing Orthogonal Frequency-Division Multiplexing (OFDM), a highly efficient multi-carrier modulation technique which enables the use of higher-order modulation schemes and Adaptive Coding and Modulation (ACM). OFDM has been adopted for current and future mobile radio communications technologies

Evaluation Of Multicarrier Air Interfaces In The Presence Of Interference For L-Band And C-Band Air-Ground Communications

The use of aeronautical vehicles and systems is continuously growing, and this means current aeronautical communication systems, particularly those operating in the very high frequency (VHF) aviation band, will suffer from severe congestion in some regions of the world. For example, it is estimated that air-to-ground (AG) communication traffic density will at least double by 2035 over that in 2012, based on the most-likely growth scenario for Europe. This traffic growth (worldwide) has led civil aviation authorities such as the FAA in the USA, and EuroControl in Europe, to jointly explore development of future communication infrastructures (FCI). According to international aviation systems policies, both current and future AG communication systems will be deployed in L-band (960-1164 MHz), and possibly in C-band (5030-5091 GHz) because of the favorable AG radio propagation characteristics in these bands. During the same time period as the FCI studies, the use of multicarrier communication technologies has become very mature for terrestrial communication systems, but for AG systems it is still being studied and tested. Aiming toward future demands, EuroControl and FAA sponsored work to define several new candidate AG radio systems with high data rate and high reliability. Dominant among these is now an L-Band Digital Aeronautical Communication Systems (L-DACS): L-DACS1. L-DACS1 is a multicarrier communication system based on the popular orthogonal frequency division multiplexing (OFDM) modulation technique. For airport surface area communication systems used in C-band, EuroControl and FAA also proposed another OFDM communication system based on the IEEE 802.16e standard, termed aeronautical mobile airport communication system (AeroMACS). This system has been proposed to provide the growing need of communication traffic in airport environments. In this dissertation, first we review existing and proposed aviation communication systems in VHF-band, L-band and C-band. We then focus our study on the use of multicarrier techniques in these aviation bands. We compare the popular and dominant multicarrier technique OFDM (which is used in cellular networks such long-term evolution (LTE) and wireless local area networks such as Wi-Fi) with the filterbank multicarrier (FBMC) technique. As far as we are aware, we are the first to propose and evaluate FBMC for aviation communication systems. We show, using analysis and computer simulations, along with measurement based (NASA) air-ground and airport surface channel models, that FBMC offers advantages in performance over the OFDM schemes. Via use of sharp filters in the frequency domain, FBMC reduces out of band interference. Specifically, it is more robust to high-power distance measurement equipment (DME) interference, and via replacement of guard bands with data-bearing subcarriers, FBMC can offer higher throughput than the contending L-DACS1 scheme, by up to 23%. Similar advantages over AeroMACS pertain in the airport surface channel. Our FBMC bit error ratio performance is comparable to that of the OFDM schemes, and is even better for our “spectrally-shaped” version of FBMC. For these improvements, FBMC requires a modest complexity increase. Our final contribution in this dissertation is the presentation of spectrally shaped FBMC (SS-FBMC). This idea allocates unequal power to subcarriers to contend with non-white noise or non-white interference. Our adaptive algorithm selects a minimum number of guard subcarriers and then allocates power accordingly to remaining subcarriers based on a “water-filling-like” approach. We are the first to propose such a cognitive radio technique with FBMC for aviation applications. Results show that SSFBMC improves over FBMC in both performance and throughput

Comparison of proposals for the future aeronautical communication system LDACS

Um zukünftigen Kapazitätsbedarf in aeronautischer Navigation abzudecken, werden neue Bord und Boden Kommunikationsdienste gebraucht. Die europäische Organisation für Sicherheit und Luftnavigation, Eurocontrol, unterstützte die Entwicklung zweier Vorschläge für ein solches System. Der erste Vorschlag, genannt LDACS1, ist ein digitales Breitband OFDM basiertes System, welches vom Institut für Kommunikation und Navigation, DLR entwickelt wurde. Der zweite Vorschlag, LDACS2 wird von einem Projektteam bestehend aus EGIS ASVIA, Helios SWEDAVIA und anderen entwickelt. LDACS2 folgt einem single carrier Steuerung mit einer GMSK Modulation. Beide Systeme sind für das Bedienen des aeronautischen Teils des L-Band (960-1164 MHz) gedacht. Diese Frequenz wird jedoch bereits von verschiedenen aeronautischen alte Systemen wie z.B. zivile Luftfahrtnavigation DME oder militärische Kommunikationssystemen (vereinigtes taktisches Informationsverteilungssystem JTIDS) eingesetzt. Darüber hinaus, LDACS ist offen für in der Luft befindlich Empfangsstörungen. Ein entscheidender Punkt im Auswahlprozess für eine der LDACS Systeme ist die Gewährleistung für das Nebeneinander von LDACS und des legacy Systems. Einerseits muss bewiesen werden, dass LDACS nur einen geringen Einfluss auf das legacy System hat. Andererseits muss eine verlässliche Funktion trotz Empfangsstörung (Beeinträchtigung) gewährleistet werden. In dieser Masterarbeit ist die Leistung von LDACS2 analysiert. Die Aufgabe umfasst einige theoretische Überlegungen für Ermittlungen von Kapazität, spektrale Leistungsfähigkeit, Skalierbarkeit und die mögliche Zahl gleichzeitiger Nutzer. Das Ergebnis zeigt die Beschränkung der angebotenen bit rates pro Nutzer gemäß der limitierten Bandbreite. Jedoch für gering bis mittelmäßigen Inanspruchnahme von Anwendern, die angebotenen bit rates sind innerhalb einer akzeptablen Reichweite. Der Hauptteil dieser Arbeit befasst sich mit der Anwendung des LDACS2 Systems gemäß der Simulations-Software. Das umfasst die gesamte physikalische Schichtung und die grundlegenden Teile der höheren Schichtung. Besonderer Schwerpunkt ist auf die Anwendung und Beurteilung von wirksamen Kanal Entzerrung Algorithms, Analyse und Auswertung. Neben AWGN Kanälen wurden auch praxisbezogenen Luftfahrtfrequenzen angewandt. Es stellte sich heraus, dass das Kanalkodierung in dieser Ausführung nicht genügend.Ilmenau, Techn. Univ., Masterarbeit, 201

Fly by data link: feasibility of a relative navigation solution for aviation relying on a future L-band data link

Trabalho final de Mestrado para obtenção do grau de Mestre em Engenharia de Electrónica e TelecomunicaçõesO presente trabalho estuda uma solução alternativa de navegação aeronáutica que contribua para a racionalização da infrastrutura terrestre de ajudas-rádio de navegação na Europa. O conceito designado de “Performance Based Navigation (PBN)” emerge actualmente ao nível da Organização Internacional de Aviação Civil, visando o aperfeiçoamento do sistema de gestão do tráfego aéreo ao nível da eficiência, segurançae capacidade. O conceito PBN promove a modernização da infrastrutura aeronáutica com base na utilização preferencial de sistemas de navegação por satélite, designadamente mediante o recurso a sinais disponibilizados pelas constelações “Global Navigation Satellite System (GNSS)”. Face às vulnerabilidades dos sistemas GNSS a interferências RF, “jamming” deliberado ou fenómenos solares, foi decidido manter uma infrastrutura de recurso/”backup”, para mitigar falhas GNSS, baseada numa redede rádio-ajudas terrestres “Distance Measuring Equipment (DME)”. Visto que estes DMEs não facultam uma boa cobertura, especialmente a baixa altitude, e tratando-se de equipamentos próximos da obsolescência tecnológica e pouco eficientes em termos de espectro rádioeléctrico, a sua racionalização requer uma tecnologia alternativa. O presente trabalho explora o recurso a novas tecnologias aeronáuticas de comunicações dados ar-solo, designadamente o futuro “data link” OFDM/TDMA de banda L (LDACS), verificando a sua adequação para suportarem as funções de navegação descritas substituindo os DMEs. Pretende-se confirmar a viabilidade com base no conceito de Navegação Relativa (RELNAV) usado em contexto militar recorrendo a filtros Kalman. As características da tecnologia LDACS são descritas e são apresentados resultados de testes do seu desempenho em termos de medição de distâncias (“ranging”). Com base nas capacidades RELNAV militares são propostos melhoramentos baseadosem filtros Kalman, simulando para demonstrar que o LDACS pode ser usado para funçãode navegação. Demonstrada a viabilidade, fica em aberto a oportunidade para sinergias que poderão viabilizar a racionalização da infrastrutura terrestre de navegação e aviónicos.Abstract: The main purpose of this work is to study an alternative solution for aeronautical aircraft navigation contributing to the rationalization of the existing European ground navigation infrastructure. The emerging Performance Based Navigation (PBN) concept, described in the document 9613 of the International Civil Aviation Organization (ICAO), calls for increased reliance on Global Navigation Satellite Systems (GNSS) (and its augmentation/differential correction systems1) but retaining ground beacons such as the Distance Measuring Equipments (DME) to cope with Global Positioning System (GPS) and GALILEO outages (e.g. jamming/solar storms). The present work will focus on demonstrating the feasibility of an alternative technology to allow the decommissioning of such DME beacons based on the re-use offuture L-Band Air Ground Data Link (LDACS) communication solutions being subject of research studies. Such data links may support the required levels of positioning, navigation and timing required to complement GNSS when the aircraft fly in an area navigation environment. This work will describe the LDACS data link technologies2 and will explain how such communications enablers would be able to support a “relative navigation” function similar to the one available in military data link technologies usinga geodetic grid. The feasibility of the proposed solution will be demonstrated on the basis of lessons learnt from military relative navigation and simulations which will evidence the technical performance/error parameters of the system in terms of ranging, bearing and horizontal positioning and other relevant QoS aspects. In addition, the multipath and co-site interference effects will be also discussed. Should the proposed solution be demonstrated as viable, it may open the door, not only for synergies leading to a more seamless aircraft equipage but also to the rationalization of aeronautical systems in the spectrum band 960-1215 MHz, which is highly congested and subject of stringent non-interference basis operational limitations