Abstract
This paper focuses on the affine frequency division multiplexing (AFDM)-enabled low Earth orbit (LEO) satellite communication, which can not only achieve seamless global coverage but also guarantee reliable multi-user access in high-mobility scenarios. On this basis, we put forward a discrete affine Fourier transform (DAFT)-domain random access preamble design scheme based on a dual-offset chirp, which concatenates asymmetric frequency-shifted chirps to significantly enlarge the available preamble pool. In particular, we reveal that, in the presence of timing offsets, the magnitude spectrum of the received preamble after matched filtering exhibits equidistant and oppositely directed peak shifts, presenting a predictable signature that enables accurate multi-user timing advance (TA) estimation. Building on this property, we further develop a segmented correlation and index reorganization-aided orthogonal matching pursuit (SCIR-OMP) algorithm for joint user identification and TA estimation. Theoretical analysis and simulation results demonstrate that the proposed scheme achieves superior multi-user detection performance compared with state-of-the-art ones.