  Augmenting ground-level communications with flying networks, such as the
high-altitude platform system (HAPS), is among the major innovative initiatives
of the next generation of wireless systems (6G). Given HAPS quasi-static
positioning at the stratosphere, HAPS-to-ground and HAPS-to-air connectivity
frameworks are expected to be prolific in terms of data acquisition and
computing, especially given the mild weather and quasi-constant wind speed
characteristics of the stratospheric layer. This paper explores the
opportunities stemming from the realization of cloud-enabled HAPS in the
context of telecommunications applications and services. The paper first
advocates for the potential physical advantages of deploying HAPS as flying
data-centers, also known as super-macro base stations. The paper then describes
various cloud services that can be offered from the HAPS and the merits that
can be achieved by this integration, such as enhancing the quality, speed, and
range of the offered services. The proposed services span a wide range of
fields, including satellites, Internet of Things (IoT), ad hoc networks (such
as sensor; vehicular; and aerial networks), gaming, and social networks. For
each service, the paper illustrates the methods that would be used by cloud
providers to offload the service data to the HAPS and enable the cloud
customers to consume the service. The paper further sheds light on the
challenges that need to be addressed for realizing practical cloud-enabled
HAPS, mainly, those related to high energy, processing power, quality of
service (QoS), and security considerations. Finally, the paper discusses some
open issues on the topic, namely, HAPS mobility and message routing, HAPS
security via blockchain and machine learning, artificial intelligence-based
resource allocation in cloud-enabled HAPS, and integration with vertical
heterogeneous networks.
