The across testbed for the future aeronautical data communications

The future airspace system is being defined by several initiatives. SESAR in Europe and NextGen in the USA are working towards the modernization of ATM procedures. The foreseen integration of remotely-piloted aircraft in unsegregated airspace is also shaping the future ATM. According to SESAR, the future Air Traffic Control (ATC; related to safety of flight) and Airline Operational Communication (AOC; related to regularity of flight) will be based on data-centric system-to-system communication, as opposed to today's voice-centric communication between pilots and controllers. ATS and AOC communication systems will rely on several ATN/IPS-based (Aeronautical Telecommunication Network/Internet Protocol Stack) air-ground data links for data-centric communication, either via satellite (e.g. Iris precursor) or directly via a ground station (e.g. LDACS, AeroMACS). Highly reliable communications between aircraft and ground will be a key factor to support the future operational procedures. Given this background, we propose erasure coding over multiple air-ground links to increase the reliability of the data communications between aircraft and ground for latency sensitive procedures. Adding redundancy and spreading the packets over multiple links reduces the end-to-end packet loss ratio and subsequently latency, even in case of link failures, at the cost of increasing the load on the airground links. ICAO defines quality of service provided to aeronautical data communications in terms of the Required Communication Performance (RCP) metric [1]. This metric is used to measure reliability at application layer with four parameters: transaction time, continuity, integrity and availability. Draft data communications requirements of future ATC and AOC services have been specified by Eurocontrol and FAA in the “Communication Operational Concept and Requirements for the Future Radio System” (COCR) document using the RCP parameters [2]. With the objective of evaluating the impact of multi-link erasure coding for meeting the RCP, a testbed has been developed in the European research project ACROSS. This testbed is an evolution of the SANDRA (Seamless Aeronautical Networking through integration of Data-links, Radios, and Antennas) European research project testbed. The SANDRA testbed implements the network aspects related to the ATN/IPS protocol stack (IPv6, MIPv6, IPsec, etc.) according to ICAO's specification in the ATN/IPS standards and recommended practices [3]. The most important feature of the ACROSS testbed for future aeronautical data communications is the Communication Performance Manager (CPM; instances of the CPM are deployed on the aircraft and on ground). This paper describes how the CPM is implemented and how it ensures that the performance, measured with the RCP, is met using the available air-ground links. The CPM employs erasure codes when necessary and forwards the encoded packets over one or more air-ground links (air-to-ground and ground-to-air). This enables the provision of higher performance than any single link could provide on its own. The performance provided by the CPM is limited by the available air-ground links characteristics and the amount of added redundancy used. In order to meet the RCP, the CPM monitors the status of the air-ground links to calculate the most efficient coding scheme for the traffic of each ATC and AOC service. The actual communication performance provided by the communications system using the CPM is evaluated in the ACROSS testbed by emulating the traffic generated by future aeronautical data communications. The testbed's ground network is composed of multiple geographical locations, so that different conditions can be configured by having the emulated aircraft fly over different regions types (airport, continental, oceanic and polar). The ACROSS testbed will be used to validate the multi-link erasure coding technique and analyze the achievable performance with the current airground data links as well as the future scenario with new air-ground links and future ATC and AOC data communications.