RFI Cancellation for an Array Radio Astronomy System With Receiver Nonlinearity

Radio frequency interference (RFI) is an important problem for a radio astronomy system (RAS) due to the very weak radio astronomical signals. Rapid expansions of active wireless systems (AWSs), as well as more demands for spectrum access by both AWS and RAS will result in scenarios with strong RFI. This will cause RAS's low-noise amplifier (LNA) to operate in a nonlinear region and impose a more challenging nonlinear RFI issue. We address this issue for RAS with the antenna array. 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. Analysis of the squared error of the RAS signal correlation estimate is also presented. The numerical results show the severe effects of nonlinear RFI and the capability of the proposed methods to keep the squared error almost as low as that of a linear system.