LoS-Aware Handover Uplink NOMA Transmissions for Multi-Layer LEO Satellite Constellation

Mega low earth orbit (LEO) high throughput satellite (HTS) constellations are regarded as one of the most important development shifts in the next generation of mobile communication systems in both industry and academia. Consider the short duration of line-of-sight (LoS) link and high dynamic topology of LEO HTSs, we propose a handover uplink non-orthogonal multiple access (Hu-NOMA) transmission scheme for a multi-layer LEO HTS constellation. First, we formulate a practical two-layer LEO HTS constellation, where the higher-layer LEO HTS has a longer LoS link duration but not always visible, and the lower-layer LEO HTS has a shorter LoS link duration and can continuous support the uplink transmission via frequent handovers. Then, we derive the closed-form expressions of ergodic capacity (EC) and outage probability (OP) for both NOMA and orthogonal multiple access (OMA) schemes. Further, we propose an improved ergodic capacity (IEC) NOMA algorithm, and terrestrial user equipments (UEs) can perform our IEC Hu-NOMA transmission according to their exponential distributed random service time, which can achieve higher EC, and have similar OP compared to the conventional OMA scheme but reduce half of the transmission time slot. Simulation results validate the accuracy of our theoretical derivations, and show that our IEC Hu-NOMA can outperform the state-of-art schemes.