MAY - 2023AEROSPACEDEFENSEREVIEW.COM19Figure 3 - Distributed SDR implementing FCIFigure 2 - Distributed flexible radio architecture conceptAIR TRAFFIC CONTROL WILL NO LONGER BE BASED ON WHERE THE AIRCRAFT "IS" BUT ON WHERE THE AIRCRAFT "WILL BE". THERE WILL BE AN OPTIMAL SYNCHRONISATION BETWEEN THE AIRBORNE-AND GROUND-BASED TRAJECTORIES, THE EXCHANGE OF TIME CONSTRAINTS A distributed SDR approach is particularly important to enable an FCI multilink concept (onboard) to ensure adequate levels of required communication performance when at least two links are in use. SDR to Boost Civil-Military InteroperabilityGreater focus on SDR technologies would facilitate military adherence to civil data link requirements, possibly on the basis of waveform accommodation and more integrative and performance-based approaches. The most recent, i.e. 5th, generation of fighters (e.g. F35 Joint Strike Fighter Lightning II) carries communication, navigation and identification (CNI) avionics suites supported by SDR technology, with conformal and adaptive (multi-frequency band) antenna arrays, which use reconfigurable FPGA (field programmable gate arrays)/RF (radio frequency) hardware and computer processors to run software which produces the desired/selected waveform(s).Distributed SDR could help to overcome military aircraft integration constraints by using a common software processing mechanism, and facilitate the implementation of FCI data link capabilities defined as waveforms. It would also facilitate co-existence with other military capabilities. A flexible radio solution for military aircraft based on SDR would avoid cumbersome military aircraft retrofits, eliminating duplicated equipage and senseless architecture configurations.State of Play and ProspectsToday, SDR is an established industry technology. SDR waveforms are highly portable between different hardware platforms, which has resulted in concepts like the Software Communications Architecture (SCA) taking advantage of open market RF integrated circuits (RFICs) and digital signal processing-intensive FPGAs.In Europe, significant industrial research on the use of SDR for aviation was conducted as part of the Single European Sky Air Traffic Management Research (SESAR), namely in Project 9.44 ­ Flexible Communication Avionics. Important follow-on technical work is being undertaken in ARINC Industry Activities/the Airlines Electronic Engineering Committee (AEEC).The final stage of LDACS validation is still ongoing in SESAR where EUROCONTROL, as a founding member of the SESAR Joint Undertaking, contributes in coordination with other industry partners. Nevertheless, distributed SDR solutions for civil aircraft have not yet been fully defined and validated. The following research gaps remain:· The distribution of the radio digital processing functions of the successive processing stages between the radio and antenna units (trade-off concerning the location of a "cutting point" in the radio functional chain);· The need to use a specific antenna and a specific analogue RF stage for each aircraft radio. This limits the possibility to update an SDR system to accommodate a new waveform via a software change only. This requires changes in frequency, bandwidth, modulation, and power and antenna polarisation. Future wide-band/multi-band RF front ends and smart/multiband antennae may make this possible in the near future;· The need to converge distributed SDR solutions with integrated modular avionics (IMA) as the latter is widely used and relies on a similar common computing platform. In the IMA core system, the functional application software is available in mass memory storage devices and is downloadable to the modules upon which they are to execute.The final stage of research and standardisation (e.g. ICAO Standards and Recommended Practices ­ SARPS) as well as industrialisation and preparatory deployment activities to bring LDACS, AeroMACS and SATCOM to the adequate level of readiness for implementation are progressing at a remarkable pace. The next implementation steps must consider distributed SDR radios in order to get these FCI technologies deployed with maximum benefits in terms of avionics optimisation and civil-military interoperability. Beyond FCI, the introduction of software radios may induce a more integrative approach through COM-NAV-SUR synergies, covering various communication exchanges supporting navigation or surveillance applications, i.e. offering backups as needed.In conclusion, SDR could have a huge transformational effect in aviation technologies by organising infrastructure development and deployment on the basis of a fully integrated and holistic approach, breaking away from the traditional technology life-cycle of aviation.
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