Uplink NOMA for Heterogeneous NTNs with LEO Satellites and High-Altitude Platform Relays

An uplink non-orthogonal multiple-access communication system is developed for heterogeneous non-terrestrial networks (NTNs) that employ both low-Earth orbit (LEO) satellite constellations and high-altitude platforms (HAPs) as relays with hybrid automatic repeat request capabilities. The system is designed as a random-access and interference-resistant network to support low-rate users. A common waveform and frequency band is used for all uplink transmissions (whether the transmitter is a user terminal or a HAP). Both theoretical and simulation-based performance analysis results are provided as a function of user transmit power and packet arrival rates for channels with interference. The use of HAP relays is shown to significantly improve throughput and reduce queue size relative to direct transmission to the LEO satellites, especially for the case of low-power users in high interference environments.