  High Altitude Platform Station (HAPS) has the potential to provide global
wireless connectivity and data services such as high-speed wireless backhaul,
industrial Internet of things (IoT), and public safety for large areas not
served by terrestrial networks. A unified HAPS design is desired to support
various use cases and a wide range of requirements. In this paper, we present
two architecture designs of the HAPS system: i) repeater based HAPS, and ii)
base station based HAPS, which are both viable technical solutions. The energy
efficiency is analyzed and compared between the two architectures using
consumption factor theory. The system performance of these two architectures is
evaluated through Monte Carlo simulations and is characterized in metrics of
spectral efficiency using LTE band 1 for both single-cell and multi-cell cases.
Both designs can provide good downlink spectral efficiency and coverage, while
the uplink coverage is significantly limited by UE transmit power and antenna
gain. Using directional antennas at the UEs can improve the system performance
for both downlink and uplink.
