Optimization of Protection Interval for Chirp Modulation in LEO Satellite Communications

In this letter, we investigate the optimized utilization of protection interval (PI) for chirp modulation in low-Earth orbit (LEO) satellite communications from two perspectives: symbol mapping, and symbol recovery with highly dynamic Doppler. Spectral analysis of the received signal reveals a distinct double-peak phenomenon under specific conditions. Based on this observation, a spectral-magnitude-assisted (SMA) symbol recovery and Doppler tracking (SR&DT) strategy is proposed to maximize PI efficiency and enhance robustness against timing errors. On the other hand, an index-concatenation-based symbol mapping (ICBSM) scheme is developed to address the Gray-incompatibility with non-dyadic PI, improving spectral efficiency with less detection performance loss. Simulation results validate the robustness of the proposed optimization against Doppler rate and timing errors in highly dynamic scenarios.