| Summary: | The carrier-to-noise ratio (<i>C/N<sub>0</sub></i>) is an important indicator of the signal quality of global navigation satellite system receivers. In a vector receiver, estimating <i>C/N<sub>0</sub></i> using a signal amplitude Kalman filter is a typical method. However, the classical Kalman filter (CKF) has a significant estimation delay if the signal power levels change suddenly. In a weak signal environment, it is difficult to estimate the measurement noise for CKF correctly. This article proposes the use of the adaptive strong tracking Kalman filter (ASTKF) to estimate <i>C/N<sub>0</sub></i>. The estimator was evaluated via simulation experiments and a static field test. The results demonstrate that the ASTKF <i>C/N<sub>0</sub></i> estimator can track abrupt variations in <i>C/N<sub>0</sub></i> and the method can estimate the weak signal <i>C/N<sub>0</sub></i> correctly. When <i>C/N<sub>0</sub></i> jumps, the ASTKF estimation method shows a significant advantage over the adaptive Kalman filter (AKF) method in terms of the time delay. Compared with the popular <i>C/N<sub>0</sub></i> algorithms, the narrow-to-wideband power ratio (NWPR) method, and the variance summing method (VSM), the ASTKF <i>C/N<sub>0</sub></i> estimator can adopt a shorter averaging time, which reduces the hysteresis of the estimation results.
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