The Statistical Analysis of C/N0 Oscillation and its E-M Solution

Carrier-to-noise density ratio or effective carrier-to-noise density ratio is the one of the most important parameters estimated within a GNSS receiver. It is compared with thresholds in different stages of receiver operation, e. g. acquisition, code- and carrier-tracking and data demodulation, in order to determine whether the state is transferred or if the measurements are reliable. Moreover, it is one of the indispensible variables in predicting receiver performance such as code-tracking accuracy or receiver implementation losses. However, previous researches only focused on asymptotic performance or computational complexity of C/N-0 estimators while the oscillatory behavior is neglected. This could be hazardous to receiver since erroneous information about signal and ambient noise may totally mislead the receiver. This paper tries to explain the reason behind C/N-0 undulation from a statistical perspective, in an attempt to find a fast and effective way to identify the phenomenon. Further, a method based on E-M method is proposed to identify the hidden states leading to C/N-0 oscillation and thus to mitigate the oscillatory measurements.