Enhanced Early Preamble Collision Detector for LEO Satellite-Based NTN IoT Random Access

In this paper, we propose an enhanced early preamble (PA) collision detector for low earth orbit (LEO) satellite-based non-terrestrial network (NTN) internet-of-things (IoT) systems to enable PA collision detection at the first step of the random access procedure. The proposed detector exploits the characteristics of NTN line-of-sight (LoS) channels, where the path gain of the LoS channel is much stronger than that of the non-LoS (NLoS) channel. Specifically, we adopt multiple detection thresholds to capture PA collisions, allowing the satellite to recognize and notify the PA collision, thereby facilitating fast random access retrials. Also, we leverage multiple root Zadoff-chu (ZC) sequences while suppressing interference, so that the probability of PA collision is significantly reduced. Moreover, we mathematically analyze the performance of the proposed detector in terms of the probability of successful PA collision detection, the probability of false collision alarm, average random access delay, and average random access-success nodes under typical NTN LoS channel conditions. Simulation results verify that the proposed multiple threshold-based early PA collision detector (MT-eCD) achieves significantly improved performance over the conventional early PA collision detection schemes in terms of random access delay, number of random access-success nodes, and resource efficiency, while satisfying the random access requirement.