Abstract: In this paper,we give the mathematical derivation for these estimation methods and discuss their tracking performance in both strong and weak signal environments.Meanwhile,a novel method,I-Branch Power-to-Variance Ratio(IBPVR),for the CNR estimation is proposed in this paper.Experiment results show that the NWPR and SNV methods do not have the saturation phenomenon when the CNR is above 50 dBHz.In weak signal environments,the SNV method has large estimation errors,whereas the NWPR and IBPVR methods have excellent estimation performances.The method IBPVR only uses the signal power in I-Branch to estimate CNR for the GNSS receivers and hence has the minimum calculation complexity among all the studied methods.