Two-Stage Preamble Detector for LEO Satellite-Based NTN IoT Random Access

In this article, we propose an enhanced random access preamble (PA) detector for the low earth orbit (LEO) satellite-based non-terrestrial network (NTN) Internet-of-Things (IoT) that efficiently detects non-orthogonal PAs while suppressing interference. The proposed detector operates in two stages to efficiently suppress the interference caused by non-orthogonal PAs. In the first stage, reconstruction and cancellation of non-orthogonal PAs are performed. In the second stage, final PA detection is performed iteratively using the reconstructed PAs and received signal. In addition, we theoretically derive the probability of PA misdetection, PA collision, and successful PA detection under typical NTN line-of-sight (LoS) channel conditions. Simulation results verify that the proposed two-stage PA detector (TSPD) achieves performance close to the theoretical upper bound in terms of successful PA detection probability. The TSPD also shows a significantly greater successful PA detection probability than the conventional PA detector using orthogonal PAs while satisfying the random access requirement for the 3rd generation partnership project (3GPP) standard. Moreover, compared to the conventional PA detector for non-orthogonal PA, which adopts an interference cancellation scheme, the TSPD achieves up to 25.6 times lower detection complexity.