Distributed RISs assisted anti-jamming communications: Is on-off status of each RIS needed?

Abstract

Owing to the broadcast nature of wireless channel, the malicious jamming poses a serious threat to wireless communications. Fortunately, due to the potential in providing multiple reconfigurable communication links, distributed reconfigurable intelligent surfaces (RIS) can establish more controllable propagation environment enhancing the anti-jamming performance compared to the single RIS. With these focuses, we establish a distributed RISs assisted anti-jamming communication system, where multiple RISs are spatially distributed to reconfigure the propagation environment, thereby enhancing the desired signals and mitigating jamming signals simultaneously. Moreover, the on-off status of each RIS is controlled, such that the best reconfigurable communication link can be selected to avoid the jamming attacks from the perspective of spatial position. Building upon the above system, the paper aims to maximize the sum rate by jointly optimizing the transceiver’s beamforming, the phase shifts of the RISs, and the on-off status of each RIS under the imperfect jammer’s channel state information (CSI). To solve the intractable problem, we adopt the discretization method to transform imperfect CSI into the worst-case one. Subsequently, an alternative optimization method is developed for beamforming optimization and RIS’s selection. Specifically, the closed-form solution of transceiver’s beamforming can be obtained by minimum-mean-square-error algorithm. Then, the successive convex approximation is adopted to optimize the phase shifts of the RISs, and a novel greed method based algorithm is proposed to determine the on-off status of each RIS. Finally, the numerical simulation results demonstrate the superiority and validity of the proposed schemes compared to existing benchmarks.