Impact of Nonlinear RFI and Countermeasure for Radio Astronomy Receivers

Abstract

Radio frequency interference (RFI) has become a critical issue to radio astronomy system (RAS) due to fast-expanding active wireless systems. A recent solution based on a coexistence paradigm offers some RFI-free durations for RAS but further expansion of RAS observation needs to cope with strong RFI. To enhance spectrum access opportunities for both wireless communications and RAS, we explore a new approach where both the systems simultaneously access the spectrum for some durations and RAS exploits RFI cancellation. The main challenge is the nonlinear distortion caused by strong RFI. We develop a signal model incorporating the nonlinearity effect and study its impact on RAS observation performance. We propose an auxiliary receiver assisted nonlinear-RFI cancellation scheme and a modified RAS signal detection scheme. Furthermore, we develop two channel estimators (unscented Kalman filter-based approach and nonlinear-to-linear mapping approach) for nonlinear systems which we apply in our RFI cancellation scheme. Analytical and numerical performance evaluation results show substantial performance advantage of our proposed methods and illustrate importance of incorporating nonlinearity in the channel estimation, RFI cancellation, and RAS signal detection.