CNR(Carrier-to-Noise Ratio),an important indicator to evaluate the navigation signal quality,which directly affected the global navigation satellite system receiver performances of signal acquisition,carrier tracking,and data demodulation.Based on the distortion model of ICAO 2OS (International Civil Aviation Organization 2nd Order Step),the analytical expressions between CNR estimation and the distortion parameters of ICAO 2OS threat model were induced by using both coherent early-late processing and non-coherent early-late processing.And the influence of distortion parameters on CNR estimation error was analyzed.Theoretical analysis and simulation results show that carrier-to-noise ratio only changes in the 10 -2 order of magnitude when the TMA(Threat Model A)parameter changes within the set range,and can reach about 0. 1 dBHz caused by the TMB(Threat Model B)parameters.When increasing the TMB oscillation frequency and decreasing the attenuation factor can increase the estimated CNR.Consequently the distortion parameters of ICAO 2OS threat model have a small influence on the CNR estimation loss.Therefore,using the output CNR of the global navigation satellite system receiver to monitor the navigation signal abnormality is not reliable.%载噪比作为评估导航信号质量的重要指标，直接影响着接收机的捕获、跟踪和电文解调性能。推导了基于国际民航组织二阶阶跃信号畸变模型下导航接收机采用相关、非相关处理时载噪比估计与畸变模型参数之间的解析表达式，并分析了畸变参数对导航接收机载噪比估计误差的影响。理论分析及仿真结果表明：数字畸变参数变化范围下导航信号载噪比变化在10－2量级，增大模拟畸变的振荡频率或者减小衰减频率将会提高载噪比估计值，模拟畸变参数变化引起的载噪比损耗可达0．1 dBHz，畸变参数对载噪比估计的影响整体上都较小，因此导航接收机的载噪比输出不能作为监测导航信号是否异常的完备检测量。
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