Can High Altitude Platforms Make 6G Sustainable?

The staggering growth of mobile traffic fostered by the spreading of 5G technology and massive Internet of Things applications is leading to the need for extensive Radio Access Network (RAN) densification. However, the entailed boost in energy consumption poses significant challenges for a sustainable transition towards 6G. High Altitude Platform Stations (HAPSs) equipped with aerial Base Stations (BSs) represent a promising and flexible solution to provide additional capacity that can be used in a flexible way to facilitate terrestrial BSs sleep modes and, ultimately, reduce energy consumption and make the network more sus- tainable. As a case study, we consider a portion of a urban RAN to investigate the potential benefits deriving from the integration of HAPSs in terrestrial RANs as a means to support joint energy and resource allocation strategies that will be needed in 6G networks. Our results show that offloading traffic to HAPS mounted BSs allows to reduce the grid energy demand of terrestrial still maintaining adequate Quality of Service.