Near-Field Directional Modulation for RIS-Aided Movable Antenna MIMO Systems with Hardware Impairments

TL;DR

This paper introduces a joint optimization framework for near-field directional modulation in RIS-assisted movable antenna MIMO systems, improving secrecy rates under hardware impairments and imperfect CSI.

Contribution

It proposes novel algorithms for discrete MA positioning and joint beamforming optimization, addressing hardware impairments and CSI imperfections in RIS-aided MIMO systems.

Findings

Achieves 28% higher secrecy sum rate under hardware impairments.

Reduces antenna count by 37.5% compared to fixed-position systems.

Demonstrates low computational complexity of proposed algorithms.

Abstract

Movable antennas (MAs) are a promising technology to achieve a significant enhancement in rate for future wireless networks. The pioneering investigation on near-field directional modulation design for a reconfigurable intelligent surface (RIS)-assisted MA system is presented, with the base station equipped with a MA array. To maximize the secrecy sum rate (Max-SSR) with hardware impairments (HWIs) and imperfect channel state information (CSI), which involves a joint optimization of beamforming vectors for confidential messages and artificial noise (AN), power allocation factors, phase shift matrices, MA positions, and receive beamforming vectors. Firstly, the transmit beamforming vectors and phase shift matrices are iteratively optimized, leveraging leakage theory and phase alignment techniques. Then, two novel algorithms for discrete MA positioning are proposed, respectively, employing uniform and compressed sensing (CS)-based non-uniform grouping strategies. Subsequently, the AN is considered and designed as the additional energy required for zero-space projection, and the receive beamforming vector is derived using the minimum mean square error (MMSE) method. The proposed algorithms have low computational complexity. Simulation results demonstrate the effectiveness of the proposed algorithms. Under HWIs and imperfect CSI, the proposed algorithm can achieve a 28\% enhancement in SSR performance while reducing the number of antennas by 37.5\% compared to traditional fixed-position antenna (FPA) systems.