Block-Cyclic Zadoff-Chu Sequences-Based Preamble Design and Detection for OTFS-Enabled LEO Satellite Random Access Systems

Low-earth-orbit (LEO) satellite communication, owing to its capability to provide ubiquitous and continuous connectivity, is expected to play a pivotal role in sixth-generation (6 G) global communication networks. Focusing on ensuring reliable access for massive users in high-dynamic satellite environments, we propose a novel random access (RA) preamble design and detection scheme incorporating orthogonal time frequency space (OTFS) modulation. Specifically, a RA preamble utilizing block-cyclic Zadoff-Chu (ZC) sequences is developed by arranging multiple single-root ZC sequences in the delay-Doppler domain with strategically configured cyclic shift sets. In particular, our design not only ensures substantial preamble capacity and low peak-to-average power ratio (PAPR), but also facilitates multi-user detection without being affected by non-orthogonal interference. By leveraging the characteristics of the proposed preamble, we introduce an effective three-stage preamble detection algorithm for accurate user identification and timing advance estimation. Moreover, we conduct theoretical derivations to analyze the impacts of preamble design parameters on the PAPR and detection performance of our scheme. Simulation results corroborate our theoretical analysis, demonstrating that the proposed scheme facilitates a flexible tradeoff between PAPR and preamble capacity by adapting the number of sequences, and significantly outperforms the existing approach in terms of the successful detection probability in typical LEO satellite scenarios.