The ANTENNAE project is developing an innovative integrated CNS solution for aircraft operating at low altitude
The ANTENNAE project explores the applicability of 3GPP 5G and next-generation hybrid terrestrial and non-terrestrial networks for providing Communication, Navigation, and Surveillance (CNS) services to aircraft operating at low altitude. The ANTENNAE project is exploring a 3GPP-compliant integrated CNS solution for Innovative Air Mobility (IAM), including piloted and U-space operations at low altitude. The solution will support safe low-altitude air traffic by providing reliable, affordable communication, navigation, and surveillance services to ensure strict adherence to flight paths, real-time traffic separation, and robust airspace boundary protection.
Why legacy CNS is not enough for low-altitude aviation
CNS is designed to provide three separate services: “C” – Communication, “N” – Navigation, and “S” – Surveillance. However, all three services rely on one common thing: wireless network infrastructure and its coverage. We need radio signals for the timely exchange of information between aircraft, between aircraft and the ground, and sometimes between ground systems. Global Navigation Satellite System (GNSS) signals help aircraft safely navigate designated routes and flight paths. Similarly, radio signals carrying critical information, including an aircraft’s location, altitude, ground speed, and surveillance data, are vital for aircraft tracking and maintaining safe separation between aircraft.
Legacy CNS is designed for manned aircraft and uses a combination of hardware, with each system dedicated to a specific service. For example, ADS-B, VDL/ACARS, transponders (Mode A/C/S), VOR/ILS receivers, and SATCOM all use different hardware and handle different services. You may think: can we use the same hardware and technologies used for manned aircraft to support CNS services for unmanned aircraft? The short answer is no, and here are the reasons.
First, legacy CNS coverage is optimised for airports and high-altitude air corridors. Due to ground structures that cause blockages, legacy CNS faces coverage problems at low altitudes. One may consider solving this challenge by expanding coverage to low altitudes through large-scale deployment of CNS infrastructure, but this would entail significant capital and operational costs. Second, it will be challenging for small, unmanned aircraft to carry fragmented CNS hardware systems and sufficient battery capacity to power multiple devices. Third, even if we successfully solve the first two problems today, how about the future? Legacy CNS systems may not have sufficient bandwidth to accommodate thousands of small automated aircraft operating at low altitudes.
ANTENNAE’s approach towards integrated CNS for low-altitude aviation
There is a pressing need for a new CNS solution for low-altitude IAM operations. We need a solution that does not require multiple onboard hardware devices, consumes less energy, and can run on small batteries. We need a solution that is highly spectrum-efficient to accommodate hundreds to thousands of aircraft flying in our urban skies at low altitudes. Let us consider a practical example. In the future, unmanned aircraft, also called drones, will be delivering food and groceries. Imagine a lunchtime period when hundreds of people working from home may order food online, and hundreds of drones may have to share the airspace as well as available radio network resources for CNS services. Therefore, the new CNS solution for unmanned aircraft must be capable of handling hundreds of aircraft simultaneously to ensure the safety of aircraft, infrastructure, and the public.
This is where the ANTENNAE project’s vision and its integrated CNS (ICNS) concept come into play. ANTENNAE project envisions delivering the “C”, “N”, and “S” services through the same technology, hardware, and frequency spectrum. This means that ICNS will eliminate the need for multiple onboard hardware systems, make efficient use of spectrum, and allow “C”, “N”, and “S” services to support and complement each other.
Today, 4G and 5G networks provide extensive coverage worldwide, with 4G covering around 90% of the global population. These cellular networks have a native ability to support massive numbers of users simultaneously. You may wonder: can these same terrestrial networks support CNS services at low altitude? According to ANTENNAE project’s exploratory research, the answer is yes, but there are some limitations.
The ANTENNAE project explores the applicability of 3GPP telecommunications standards for delivering ICNS services at low altitude to support both piloted and U-space operations. It is worth emphasising that coverage of 5G terrestrial networks is optimised to serve users located on the ground, on streets, and in buildings. Researchers outside the ANTENNAE consortium have conducted real-world experimental measurements which confirmed the feasibility of connecting an unmanned aircraft to a 5G base station. However, there is a noticeable performance degradation as aircraft altitude increases because these base stations use down-tilted antennas.
This presents a considerable design challenge for future networks. How can CNS services be delivered to aircraft when they fly beyond the coverage of terrestrial networks? This is where non-terrestrial networks, especially direct-to-device connectivity, become important. To complement the poor coverage above terrestrial base stations, the ANTENNAE solution uses 3GPP hybrid terrestrial and non-terrestrial networks to ensure continuous coverage for CNS services. In particular, the ANTENNAE solution uses direct-to-device connectivity, which allows a transceiver on the aircraft to automatically switch to a satellite connection when the aircraft moves outside terrestrial network coverage without interrupting CNS services.
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