Two-Step Joint Timing and Frequency Synchronization Scheme for LEO Satellite via Chirp Signals

Abstract

This paper investigates a two-step joint synchronization algorithm based on the Chirp signal. We first establish a Low Earth Orbit (LEO) channel model that incorporates time-frequency selective fading, characterized by severe Doppler kinematics, multipath propagation, and atmospheric scintillation. Then we propose a two-step estimation architecture to address the computational bottlenecks of high-precision joint synchronization. In the initial stage, we acquire coarse offset boundaries via up-Chirp and down-Chirp matched filtering, while in the fine stage we apply an improved Linear Success-History-based Adaptive Differential Evolution (LSHADE) algorithm. Furthermore, we introduce an adaptive segmented processing strategy with a linear parameter contraction mechanism to constrain the memory footprint, seamlessly aligning with real-time Ping-Pong buffering constraints. Numerical simulations demonstrate that the proposed scheme provides robust estimation accuracy, outperforming benchmark methods in low signal-to-noise ratios (SNRs) with lower computational complexity.