The Ground Based Augmentation System (GBAS) is the cornerstone for enabling automated landings without the Instrument Landing System (ILS). Currently GBAS is evolving to GAST-D for CAT III landings. This extends GBAS via the use of multiple frequencies (L1/L2 and L5) and the use of multiple global navigation satellite system constellations. GBAS requires correction data to be broadcast to aircraft. This is currently done with the VHF Data Broadcast (VDB) datalink. However, VDB has several known shortcomings: (1) low throughput, (2) small area of operation and (3) no cyber-security measures. In this paper we propose the use of the L-band Digital Aeronautical Communications System (LDACS) for broadcasting GBAS correction data to address these shortcomings. In flight experiments conducted in 2019, we set up an experimental GBAS installation using LDACS. Broadcast data was secured using the TESLA broadcast authentication protocol. Our results indicate that cryptographically secured GBAS data via LDACS can provide GAST-C and GAST-D services with high availability if cryptographic parameters are chosen appropriately.

The L-band Digital Aeronautical Communications System (LDACS) is a key enabler of the new air traffic services and operational concepts necessary for the modernization of the air traffic management (ATM). After its initial design, compatibility tests with legacy L-band systems, and functional demonstrations in the laboratory, the system is currently undergoing the standardization process of the International Civil Aviation Organization (ICAO). However, LDACS has not been demonstrated in flight yet. In this paper, we present the first in-flight demonstration of LDACS, which took place in March and April 2019 in southern Germany and included four LDACS ground stations and one LDACS airborne station. We detail the experimental setup of the implemented LDACS ground and airborne stations together with the flight routes, the conducted experiments, and the frequency planning to ensure compatibility with legacy systems. In addition, we describe the demonstrated ATM applications and the security measures used to protect them. Based on the obtained measurement results, we evaluate the LDACS in-flight communication performance for the first time, including the achieved communication range, the measured end-to-end message latency, and the LDACS capability to provide quality of service by effectively prioritizing safety-relevant data traffic. Furthermore, we use the in-flight received signal power to assess the applicability of a theoretical path loss model. These flight trials contribute to the final steps in the development of LDACS by providing its in-flight communication performance and by demonstrating: first, its correct functionality in a realistic environment; second, its capability of supporting ATM applications and the advanced security measures that can be used to protect them; and third, its spectrum compatibility with legacy systems. We conclude that LDACS is ready to support ATM operations and that LDACS frequency planning can safeguard legacy systems successfully.

The L-band digital aeronautical communications system (LDACS) is a cellular air-ground data link for air traffic control. It is a corner-stone of the future aeronautical communications infrastructure. LDACS shall operate in the frequency band 960-1164 MHz under the constraint of secondary spectrum usage. This implies strict spectral, power, and spatial separation towards current legacy systems operating in this frequency band. It has been proposed to fulfil these restrictions using cell planning for LDACS without changing frequency allocations of the legacy systems. However, the feasibility of such a cell planning has yet to be demonstrated. In this paper we demonstrate the feasibility of LDACS cell planning under these constraints. For this purpose we introduce the theoretical limits for such a separation enabling the co-existence of LDACS and DME (distance measuring equipment system: the primary user) in the same frequency band. Closed-form expressions are obtained such that the proper operation of DME is not harmfully affected by LDACS. These expressions are utilized in the first step to find DME-compliant locations for LDACS ground stations. In the second step, interference constraints within LDACS itself are defined and applied. This approach yields DME-compliant locations of LDACS ground stations with channel assignments fulfilling the interference constraints. The application of our method shows that LDACS cell planning in Europe is possible without disturbing the proper operation of the DME system.Index Terms-L-band digital aeronautical communications system (LDACS), distance measuring equipment (DME), cell planning, channel assignment, Hopfield networks.

The L-band digital aeronautical communications system (LDACS) is the future air-ground communications technology currently undergoing the International Civil Aviation Organization (ICAO) standardization process. As LDACS is intended to operate in the frequency band 960-1164 MHz, compatibility tests between LDACS and the legacy systems operating in this frequency band are necessary to ensure that no system is harmfully interfered. One of these systems is the joint tactical information distribution system (JTIDS), a technology employed by the tactical data link Link 16. In this paper, we present the results of an impact assessment of LDACS on JTIDS conducted through simulations. The extent of the impact has been quantified by simulating a wide variety of interference configurations, which are expected to cover most realistic interference conditions between LDACS and JTIDS. Baseband simulation models of both systems have been implemented and an interference scenario between LDACS and JTIDS has been defined. To evaluate the impact, the degradation of the signal-to-noise ratio (SNR) of JTIDS by the presence of LDACS has been determined. Default JTIDS transmissions, where the information is repeated at distant frequencies, do not show a significant degradation by the presence of strong LDACS interference, with an SNR loss lower than 1 dB in any considered interference scenario. Comparatively, a certain dependency on the specific LDACS deployment is noticeable for less protected JTIDS transmissions. Based on the observed interdependencies, recommendations for the deployment of LDACS are given in this paper, such that the impact of LDACS on JTIDS is minimized.Index Terms-Future communications infrastructure (FCI), interference, L-band digital aeronautical communications system (LDACS), Link 16, multifunctional information distribution system (MIDS), tactical data link (TDL), joint tactical information distribution system (JTIDS).

The increasing air traffic foreseen for the next decades has triggered an extensive modernization of the air traffic management. Specifically, new air traffic services and operational concepts have been defined and shall be supported during all phases of flight by a set of modern digital data links integrated into a single communications network named the Future Communications Infrastructure (FCI). The air-to-air (A2A) component of the FCI, the L-band Digital Aeronautical Communications System (LDACS) A2A mode, is currently in the initial stages of its development. Given that the LDACS A2A mode must be able to operate without any ground or satellite support, the data link must provide means for the aircraft to establish and organize an independent communications ad-hoc network, which imposes a great challenge for the design of the data link and specially for its medium-access control. In this paper, we contribute to the development of the LDACS A2A mode by assessing the performance of an A2A data link based on two different mediumaccess protocols; ALOHA with and without diversity, and a self-organizing time-division multiple-access (STDMA) scheme. The performance is obtained by simulating the implemented models of both the ALOHA-based and the STDMA-based A2A data link for different design parameters, requirements, and air traffic conditions. The obtained results show that the STDMAbased A2A data link performs better than the ALOHA-based A2A data link in most considered cases, given than the former requires a lower bandwidth than the latter to achieve the desired performance. Based on our analysis, we conclude that STDMA is a better candidate than ALOHA with or without diversity for the medium-access control of the LDACS A2A mode.

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