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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - DroC2om (Drone Critical Communications)

Teaser

Summary

The Drone Critical Communications (DroC2om) project targets the data link of the Remotely-Piloted Aircraft Systems (RPAS) / Unmanned Aerial Systems (UAS); RPAS is the terminology used by the international aviation-related agencies, and UAS is a commonly accepted terminology for the same. DroC2om considers RPAS/UAS data links in Very Low Level (VLL) airspace, i.e. for unmanned aircraft operating up to heights of 500 feet, where the aircraft is typically referred to as a drone. For society, the use of drones is expected to bring innovation, new services for citizens, new business models and economic growth, cf. the SESAR U-Space vision. For these expectations to materialize, the U-Space vision aims to integrate the operation of drones into civil airspace, i.e. enabling the sharing of the airspace between manned and unmanned aerial systems based upon a number of functions and specific procedures for airspace access that rely on a high level of digitalization and automation. The ability to reliably exchange Command and Control (C2) information over a wireless data link is crucial to several of these functions and procedures.
The C2 data link needs to ensure a high level of reliability (availability and integrity) across a wide range of operating environments. The underlying hypothesis of the DroC2om project is that such reliability can be provided by relying on the coverage provided by the combination of terrestrial cellular and satellite networks. The C2 data link may use both cellular and satellite data links, or any one of them, depending on the required link performance. However, the use of cellular for C2, and the required mechanisms for maintaining a reliable link, are not well understood at this stage. Furthermore, the integration between cellular and satellite has not yet been given attention. Therefore, the DroC2om studies the use of existing cellular and satellite infrastructure for the C2 data link, using measurements, live flight trials, and simulation evaluation. Based on this, an integrated cellular-satellite architecture for data links is designed.
The project has shown that both existing satellite and cellular systems can support C2 data link communication. This is true in scenarios with low load from terrestrial users for the cellular case, but may require enhancements under higher cellular load scenarios. For the satellite case, support is ensured by design. Cellular system enhancements can be implemented on the drone side with moderate implementation complexity. The proposed hybrid integration with geosynchronous satellite systems, combine low latency and coverage with reliability for robust C2 performance.

Work performed

The project is structured in six Work Packages with WP2 to WP5 representing the technical core of the project. In WP2, initial scenarios and requirements have been definedand later updated to align with the formalization and gained understanding of the U-Space concept. The architecture for a hybrid satellite and terrestrial cellular system has been conceived and captured in the form of a model, encompassing both the architectural and functional aspects of the U-Space Service provision while highlighting the role of the C2 Link in the frame of U-Space.
The architecture is aligned with the activities performed in the frame of WP4 on the subsystem and network level, where the models have been further enhanced to encompass technology specific solutions. Particularly, a combined cellular LTE/5G and satellite system concept to provide optimal support for both terrestrial communications and high reliability drone data links have been outlined, including in-depth cellular and satellite network architecture and mechanisms related to C2 data link provisioning. Much of this work has been used to impact 3GPP and EUROCAE standardization in connection with release 15 support for aerial vehicles and MOPS production. Several of the findings have been published in the scientific literature. The work has also detailed the architecture for the integrated cellular-satellite data link connectivity, including a functional analysis of the overall architectural elements and the link selection mechanism, along with a study on the suitability of several state-of-the-art solutions for ensuring the required scalability and mobility in the concept. A live demonstration of the hybrid concept, was published on YouTube in Summer 2018, and has since had more than 8500 views.
In support of the activities in WP4, and the projectâ€™s simulation and demonstration environment developed in WP3, WP5 has included two measurement campaigns to characterize the terrestrial â€˜cellular network to droneâ€™ communication channel. The measurement campaigns have added solid empirical evidence on the drone to cellular network channel in urban areas, for what concerns the large-scale propagation and interference characteristics of the channel, as well the dynamics of the channel. The results have clearly shown that interference mitigation measures are crucial to cellular C2 provision in U-Space. Several of the results have been published in the scientific literature.
The simulation environment for the project demonstrator and final evaluation of the hybrid cellular-satellite C2 data link solution in WP3, has implemented a realistic scenario based on existing cellular network deployment data, propagation modelling, cellular network traffic and interference modelling, and geosynchronous satellite beam coverage in the Baltic Sea region. A web application was developed to interactively visualize and explore the simulation results, emphasizing particularly two application-level C2 performance indicators which capture the quality of the simulated C2 link.
Besides the impact to 3GPP specification work, the project has participated to EUROCAE standardization, in discussions and with input to MOPS on C2 Link and guidance on use of spectrum. Also, besides a total of seven scientific publications, several of the project results have been disseminated in scientific and/or industry events.

Final results

The project has outlined architectural elements of an integrated hybrid cellular-satellite concept which, although relying mainly on state-of-the-art solutions, was not previously investigated; the hybrid cellular-satellite architecture combines low latency and coverage of cellular with reliability of satellite communications for robust C2 performance. For this concept, several low to moderate complexity solutions, including multi-link connectivity and beam switching, for ensuring drone C2 link quality in highly loaded cellular networks were proposed and documented. Predominantly, these enhancements can be implemented without modification of existing systems, or , when modification is required, limiting the changes to the drone side, thereby ensuring a fast roll-out of the U-Space services.
The project has contributed solid empirical evidence on the drone to cellular network channel, adding new findings on the dynamics of the channel. These, together with the first results on the architecture and mechanisms for link quality enhancement, provide the basis for in-field evaluation of the concept to validate the project results in practice, as well as continued research activities to study these under greater detail.