The parameter analysis of satellite tracking, telemetry, and command signal is necessary for space situational awareness. Unified S-Band (USB) waveforms are widely used in space missions. As a crucial parameter of the USB waveform, the modulation index influences the power distribution and spectrum characteristics of the waveform. This paper proposes two novel blind estimation methods of the modulation index based on spectral analysis. The equations for estimating the modulation index are constructed by the relation between the spectral characteristics and the Fourier transform of signal. The theoretical analysis of the estimation error of the methods is derived. The factors that influence the estimation error are investigated by Monte Carlo simulation, and an actual Geostationary Earth Orbit satellite signal is used to verify the methods. The proposed methods have lower complexity than existing methods, while also providing more than 10 times accuracy improvement at low signal-to-noise ratios. Suggestions for the application of the proposed methods to different scenarios are also provided.

卫星跟踪、遥测和指挥信号的参数分析是空间态势感知的必要条件。统一 S 波段 (USB) 波形广泛用于太空任务。调制指数作为USB波形的一个关键参数，影响着波形的功率分布和频谱特性。本文提出了两种基于频谱分析的调制指数盲估计方法。调制指数估计方程由信号的频谱特性与傅里叶变换之间的关系构成。推导了方法估计误差的理论分析。通过蒙特卡洛模拟研究了影响估计误差的因素，并使用实际的地球静止轨道卫星信号对这些方法进行了验证。所提出的方法比现有方法具有更低的复杂性，同时还在低信噪比下提供了 10 倍以上的精度提高。还提供了将所提出的方法应用于不同场景的建议。