PRACH in Self-Powered Satellite Internet of Things: Low-Cubic Metric Preamble Design and Detection

This article focuses on the energy-efficient physical random access channel (PRACH) design for self-powered sensors integrated satellite Internet of Things (S-IoT), where two novel preamble design schemes are proposed by jointly considering cubic metric (CM) reduction, coverage enhancement, resistance to carrier frequency offset (CFO), and low-complexity detection. Specifically, both the schemes possess a uniform preamble format by repeatedly cascading a series of conjugate Zadoff–Chu sequence pairs in the frequency domain, which can effectively mitigate the adverse effect of large CFO under the premise of ensuring PRACH coverage. Furthermore, phase rotation optimization and inverse discrete Fourier transform (IDFT) scaling are, respectively, leveraged in the two schemes to cope with the problem of CM performance degradation caused by sequence repetitions. We also develop the corresponding preamble detection mechanisms that are capable of performing joint timing advance (TA) and CFO estimation and conduct mathematical analysis in terms of CM and maximum coupling loss. Simulation results verify the feasibility of our schemes in self-powered S-IoT and demonstrate that with the increment of the number of sequence repetitions, the proposed schemes can maintain relatively lower CM values in comparison to the state-of-the-art ones, while having significantly enhanced PRACH coverage and detection performance.