The first year of the project was primarily focused on developing the initial concept elaborating the operational use cases targeted by the project and further analyzing their operational needs. This was complemented by thorough state-of-art studies in individual technological areas:
• Communication – focusing primarily on mobile RF technology (4G and 5G) and its comparison with existing aviation links;
• Navigation – focusing on network based positioning, GNSS limitations, and fusion of inertial and GNSS navigation systems.
• Surveillance - exploring low power ADS-B concept together with associated operational requirements, as well as capabilities of the latest low cost millimeter Wave (mmW) sensors for obstacle detection.
In addition, a dedicated study of current certification process and possible new approaches was performed.
In the second half of the project the proposed technical solutions/concepts were further developed and validated through extensive sets of simulations and selected elements also demonstrated through project’s flight demo.
In communication area, the focus was done primarily on evaluation of various interference limiting techniques for cellular network data-link and possible benefits of mmWave channels introduced in 5G. Furthermore, usability of cellular network datalink for potential services supporting GA/R operations was analyzed.
4G and 5G cellular systems seem to be very promising technologies to support communications in GA/R. The Time Division Duplexing (TDD) scheme is a good candidate for GA links due to the channel reciprocity and high time correlations in TDD links. Multiple-Input Multiple-Output (MIMO) together with beamforming techniques may bring significant benefits to the aerial users, in terms of reliability and throughputs. The co-existence of cmWave and mmWave communications would be recommended for the communication links in GA/R, as mmWave-links alone suffer of high path losses and are not suitable to altitudes above few hundred of meters. The Orthogonal Frequency Division Multiple Access (OFDMA) is a good multiple access scheme candidate for GA links, but the novel Non-Orthogonal Multiple Access (NOMA) scheme has the potential to outperform OFDMA for GA links.
It is expected that, even in a near future of multi-constellation GNSS (with over 3 constellations available), GNSS only navigation will not be able to guarantee sufficient service availability in urban and sub-urban areas for aerial applications. Navigation work addressed a series of simulations evaluating possible fusion of Global Navigation Satellite System (GNSS) with a supplementary position methods (Inertial Navigation System (INS) and/or 4G positioning reference signals) complemented with Integrity Monitoring algorithms to provide a robust navigation solution primarily targeting rotorcraft use cases.
Results have shown that network-based navigation by means of 4G positioning reference signals can deliver in areas with densely distributed 4G network a range positioning accuracy comparable to the GNSS or only slightly worse. Therefore, we concluded that network RF signals can successfully replace GNSS signals in urban areas where sky visibility is obstructed and GNSS-only navigation would be unavailable. Integration with INS was then found particularly helpful in enhancing the integrity of the navigation solution.
The proposed and evaluated low-cost low-power ADS-B concept seem to answer well airborne surveillance needs of heterogenous traffic in low airspace. The experimental prototype of low power ADS-B transceiver was successfully tested and demonstrated during project’s flight demo. Preliminary feasibility discussion of alternative certification approach did not identify technical blocking points for its application to low altitude ADS-B concept.
Evaluation of new mmWave radar developed for automotive industry show that it is able meet majority of obstacle detection requirements for low speed phases of rotorcraft flights. Results also indicate importance of complementary detection means for phases of flights with higher speed – such as maps/databases of terrain and ground obstacles (also explored in the project), and cooperative surveillance for flying objects with small radar cross-section (e.g. drones).
Obtained results thus indicate that affordable surveillance solutions for low altitude operations should consider combination of multiple COTS technologies in order to meet relevant operational requirements.
