Outdoor-to-indoor propagation characterisation and the experimental Hypercell platform

The IP led the experimental evaluation of outdoor-to-indoor coverage from aerial base-station geometries and the construction of the Hypercell experimental platform, providing the experimental foundations required for subsequent modelling and optimization activities.

The first task consisted of outdoor-to-indoor propagation campaigns to quantify indoor coverage from aerial base stations (acting as Hypercells). As this work was carried out before the final Hypercell prototype was available, and since professional channel sounding equipment could not be safely integrated into a drone platform, the aerial geometry was emulated by placing a 30 dBm transmitter on a roof mast at two heights, 6.5 m and 9 m above the roof. The campaign was conducted at Universidad de Granada (CITIC-UGR) [E1.8], covering 2, 3, 7, 10 and 14 GHz across three indoor floors, with more than fifty receiver locations.

Based on this dataset, the team developed a new empirical multifloor outdoor-to-indoor propagation model, combining three-dimensional distance, frequency, floor-dependent attenuation and shadowing statistics. The resulting model achieved prediction errors below 4 dB RMSE across the evaluated bands and showed that aerial base stations can effectively provide indoor coverage at 2, 3 and 7 GHz, while 10 GHz requires favourable propagation conditions and 14 GHz presents strong penetration limitations.

Building upon this propagation knowledge, the IP led the construction and experimental validation of a complete Hypercell platform using commercial 5G equipment. The developed platform extends the existing UPV private 5G infrastructure through the integration of a new portable Hypercell node, including the required Open5GS core configuration and a commercial Nokia AirScale radio access unit operating in the n40 band. A lightweight Nokia pico remote radio head was integrated with a DJI Matrice 350 RTK tethered drone, enabling the deployment of an aerial base station based on commercial equipment, complementing earlier software-defined-radio tests.

The platform was experimentally validated at the Universitat Politècnica de València by simultaneously operating terrestrial and aerial cells. Engineering smartphones and professional RF scanners were used to monitor radio coverage, throughput and key performance indicators in outdoor and indoor environments. These experiments demonstrated the practical feasibility of integrating commercial 5G infrastructure into a tethered aerial platform and provided the first experimental validation of the Hypercell concept under realistic deployment conditions.