Near-field multiuser secure communication via dynamic metasurface antenna

The near-field multiuser secure communication system is investigated in this paper, where dynamic metasurface antennas (DMAs) are deployed at the base station to communicate with multiple users under the threats of multiple eavesdroppers. To ensure the safety performance of the system, the minimum secrecy rate is maximized by jointly optimizing the DMA weight matrix and digital precoder under the constraints of transmit power and the Lorentzian phase of DMA. A two-stage algorithm is proposed to address the nonconvex optimization problem. In the first stage, the fully digital (FD) beamformer is designed using successive convex approximation technique. In the second stage, the Euclidean distance between the FD beamformer and the DMA-based beamformer is minimized. To this end, the DMA weight matrix and the digital precoder are alternatively optimized by the block coordinate descent approach. In numerical simulations, the DMA-based beamforming design achieves better performance than the conventional partially connected phase-shift-based hybrid analog/digital beamforming design.