Interference Cancellation and Distortion Compensation in Non-Linear Regime




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Receivers in radio astronomy system (RAS) are very sensitive to radio frequency interference (RFI). Due to the fast expansion of active wireless systems, RFI becomes a critical issue for RASs. Strong RFI can cause an RAS’s low noise amplifier (LNA) to operate in its nonlinear region causing nonlinear distortion for the received signal. We address this issue for both single dish RAS and array RAS. For single dish RAS, we develop a signal model that incorporates 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. For array RAS, we develop a new signal model at the output of RAS array processing when the LNA at each RAS receiver behaves nonlinearly. We show that the two existing methods to address RFI in RAS array systems fail to deal with the nonlinear RFI. Next, we propose two modified methods to address the nonlinear RFI. Analytical and numerical evaluations are carried out to show the severe effects of nonlinear distortions and show that our proposed methods are capable of achieving a substantial performance advantage.



Radio astronomy, Radio -- Interference, Low noise amplifiers, Nonlinear theories, Kalman filtering


©2020 Mahmoud Esam Mohamed Ahmed Abdelgelil. All rights reserved.