HAPS Platforms as a Complementary Stratospheric Connectivity Layer
HAPS platforms operate in the stratospheric layer, typically between 17 and 22 kilometres of altitude, in a region where atmospheric conditions permit prolonged stationary or quasi-stationary flight. This position confers upon them a coverage footprint significantly larger than that of a conventional ground station, but with link latencies considerably lower than those of geostationary orbit systems. The combination of both properties places HAPS in a distinct functional position within the non-terrestrial network architecture defined in 3GPP standards, where they are assigned specific treatment as an aerial access node. From the perspective of radioelectric propagation, HAPS may operate in bands authorised for high-altitude fixed and mobile services, subject to coordination with the ITU and the competent national administrations. Spectrum management represents one of the most relevant operational constraints, as coexistence with terrestrial networks in shared bands requires geographic and temporal coordination mechanisms that increase deployment complexity. The stability of the platform at altitude, whether through solar electric propulsion or autonomous flight systems, directly determines the quality of antenna pointing and, consequently, link performance. In coverage scenarios for remote or difficult-to-access areas, HAPS offer service capabilities where terrestrial infrastructure is technically or economically unviable. This characteristic is particularly pertinent in emergency management contexts, where the availability of a persistent aerial node makes it possible to maintain command and control connectivity without relying on fixed infrastructure that may have become degraded. Integration with terrestrial 5G networks requires standardised interfaces and adequate backhaul, conditions that determine the actual scope of the platform's capabilities in each mission configuration. The European regulatory framework, through CEPT and in coordination with EASA for airworthiness aspects, continues to develop the operating conditions for these platforms in non-segregated airspace. Regulatory maturity is currently one of the limiting factors for the systematic operation of HAPS in civil environments, alongside the certification requirements for propulsion systems and the procedures for unmanned air traffic management. The operational feasibility analysis of a HAPS must consider these constraints in an integrated manner together with link and coverage requirements.
NASSAT - Network Satellite Systems