Maximum Theoretical Interference Mitigation Capability of a GNSS Receiver as Limited by the GNSS Frontend

One key element for the performance of a GNSS receiver is the quality of the frontend. Each degradation occurring there can’t be gained back by signal processing algorithms anymore. Typical parameters for GNSS frontends are the overall noise figure, group delay variation, clock stability, non-linearity and AGC control, which keeps the quantization noise a small as possible. Frontends are also designed for robustness against RF-interferences (RFI). The level of robustness depends on the application of the GNSS receiver. Interference suppression within a GNSS receiver is often performed in the digital part of the receiver. Adaptive filters are used making use various signal processing techniques like time-domain methods (e.g. FIR, IIR, pulse-blanking) or transformation methods (e.g. Fourier). For all those methods it is important that the digital signal represents the analog received signal as close as possible. Only then a clear separation of the GNSS signal, RFI and thermal noise can be drawn. If this is achieved, then - for example - sharp notch filters can be used to eliminate a continuous wave interference. If, however, there is only one element in the frontend chain operating in the non-linear region, the mitigation algorithm will suffer in its performance. Overall, the frontend limits the RFI mitigation capability of a GNSS receiver, regardless which digital signal processing algorithm is used. It is thus of interest to quantify this limit. This limit is then an upper bound of the RFI mitigation capability and will be reached if the best possible digital signal processing algorithm is used. In this paper, we like to introduce a method to calculate the maximum theoretical mitigation capability (MTMC) based on the parameters of each element in the frontend. A good reason to use this figure-of-merit compared to the common ones like the maximum I/N0 or I/S is, that the MTMC is more intuitively for the user of a receiver. It is easier to capture the SNR degradation and what he can gain back through mitigation, rather than understanding all the other effects like power, distance, angle of arrival of the RFI source and the antenna characteristics. With the MTMC it is understandable what the capability of the hardware is and later how effective the digital signal processing mitigation performs compared to the hardware performance.