Digital Spectral Separation Coefficient (SSC) for GNSS Signal to Noise Measurements and Interference Detection

In a GNSS receiver the capability to measure the carrier power to noise density (C/N0) with a high level of accuracy and to detect the presence of interfering signals are two very important activities. The C/N0 parameter is not only important for determining the system performance and for the integrity monitoring, but also for the control of the receiver behavior: in fact an early interference detection and a reliable estimation of the spectral characteristics of the disturbing signal allow the activation in the receiver chain of specific mitigation blocks that can significantly enhance the receiver performance. This work presents an extension of the SSC theory introduced by J. W. Betz to evaluate the effects of an interfering signal in a GNSS receiver. The SSC parameter is an element of the “effective C/N0”, which is a parameter able to take into account the interference effects in the measurement of the carrier to noise ratio. In order to evaluate the “effective C/N0” it is necessary to know not only the SSC, but also other power parameters of the received signal, that is the signal power, the noise spectral density, and the interfering power. In the paper an alternative definition of the SSC is provided, based on the autocorrelation functions. This new definition has allowed the development of a new estimation algorithm that allows the determination of the other power parameters. Simulation tests have proved the effectiveness of the proposed method. The developed method is also adequate for the interfering detection: in fact it can be opportunely modified in order to test if an interfering is present or not. The detection algorithm has been tested by simulation, and the obtained results prove that the method is able to well discriminate the two cases of presence and absence of interfering.