RIS-Aided Wideband Holographic DFRC

To enable nonline-of-sight (NLoS) sensing and communications, dual-function radar-communications (DFRC) systems have recently proposed employing reconfigurable intelligent surface (RIS) as a reflector in wireless media. However, in the dense environment and higher frequencies, severe propagation and attenuation losses are a hindrance for RIS-aided DFRC systems to utilize wideband processing. To this end, we propose equipping the transceivers with a reconfigurable holographic surface (RHS). Unlike RIS, an RHS is a metasurface with an embedded connected feed deployed at the transceiver for greater control of the radiation amplitude. This surface is crucial for designing compact low-cost wideband wireless systems, wherein ultramassive antenna arrays are required to compensate for the losses incurred by severe attenuation and diffraction. We consider a wideband DFRC system equipped with an RHS at the transmitter and an RIS reflector in the channel. We jointly design the receive filter along with the digital, holographic, and passive beamformers to maximize the worst-case radar signal-to-interference-plus-noise ratio (SINR) while ensuring the communications SINR among all users. For the resulting nonconvex optimization problem, we develop an alternating maximization method to decouple and iteratively solve these subproblems. The resulting nonconvex optimization problem involves maximin objective, constant modulus, and difference of convex constraints. We develop an alternating maximization method to decouple and iteratively solve these subproblems. Numerical experiments demonstrate that the proposed method achieves better radar performance than non-RIS, random-RHS, and randomly configured RIS-aided DFRC systems.