Golay Sequence-Based Preamble Design for Grant-Free Random Access in Satellite-ISAC-Empowered C-IoT Networks

Emerging consumer Internet of Things (C-IoT) networks require reliable and low-overhead connectivity, which positions satellite-based integrated sensing and communication (ISAC) systems as a promising solution. Owing to its low signaling overhead and short access latency, grant-free random access serves as a key technology in such systems, leveraging joint activity detection and channel estimation (JADCE) to enable connectivity without prior scheduling. Given the sporadic traffic of massive C-IoT devices, the JADCE can be reformulated as a sparse signal recovery problem, which is solved through compressed sensing (CS) algorithms. However, the application of CS remains constrained by the preamble-based sensing matrix, where existing sequence designs fail to provide both scalability and low coherence, and incur high computational complexity under massive access. To resolve this, we present a semi-orthogonal Golay preamble sequence design scheme for satellite-ISAC-empowered C-IoT networks. Specifically, we synthesize heterogeneous binary Golay sequences through a nested construction to expand sequence dimensionality while preserving low coherence. To further support efficient CS-based JADCE, a group-based adaptive variable-step recovery algorithm is developed to exploit the specific sequence structure for efficient detection. In addition, to ensure practicality for power-limited C-IoT devices, a genetic algorithm optimizes sequence permutations for peak-to-average power ratio (PAPR) reduction and provides closed-form bounds for both PAPR and coherence. Simulation results show that, compared with existing sequence designs, the proposed scheme achieves competitive JADCE accuracy, low PAPR, and low coherence, enabling reliable and efficient access for massive C-IoT devices in satellite scenarios.