Reconfigurable Intelligent Surface-Enabled Array Radar for Interference Mitigation

Conventional active array radars often jointly design the transmit andreceive beamforming for effectively suppressing interferences. To furtherpromote the interference suppression performance, this paper introduces areconfigurable intelligent surface (RIS) to assist the radar receiver becausethe RIS has the ability to bring plentiful additional degrees-of-freedom. Tomaximize the output signal-to-interference-plus-noise ratio (SINR) of receivearray, we formulate the codesign of transmit beamforming and RIS-aided receivebeamforming into a nonconvex constrained fractional programming problem, andthen propose an alternating minimization-based algorithm to jointly optimizethe transmit beamformer, receive beamformer and RIS reflection coefficients.Specifically, we offer the closed-form optimal solutions of transmit andreceive beamformers according to the minimum variance distortionless responseprinciple, and translate the RIS reflection coefficients design into a seriesof unimodular quadratic programming (UQP) subproblems by employing theDinkelbach transform. To tackle the UQP subproblems efficiently, we propose asecond-order Riemannian Newton method (RNM) with improved Riemannian Newtondirection, which avoids the line search and has better convergence speed thantypical first-order Riemannian manifold optimization methods. Moreover, wederive the convergence of the proposed codesign algorithm by deducing theexplicit convergence condition of RNM. We also analyze the computationalcomplexity. Numerical results demonstrate that the proposed RIS-aided arrayradar has superior performance of interference suppression to the RIS-free one,and the SINR improvement is proportional to the number of RIS elements.