AFDM Based Random Access Preamble Design and Detection for LEO Base Stations

Low Earth orbit (LEO) satellite communication offers significant advantages over terrestrial communications, characterized by its cost-effectiveness and extensive coverage. Nevertheless, the relative motion between LEO satellites and user terminals results in a larger frequency offset compared to terrestrial communications. Meanwhile, the maximum round-trip delay within the satellite communication beam is considerably greater. To address these challenges, this paper first proposes a novel preamble based on the Zadoff-Chu sequence and creatively utilizes Affine Frequency Division Multiplexing (AFDM) waveforms for the transmission of the preamble for the first time. Subsequently, to enhance the accuracy of timing advance (TA) detection, a detection algorithm is proposed to distinguish the first-path delay. Finally, the simulation results confirm that the AFDM based preamble outperforms the preambles based on Orthogonal Frequency Division Multiplexing (OFDM) in mitigating the impact of frequency offset in LEO satellite communication without the requirement of pre-compensation.