Optimizing Movable Antenna Position and Transmissive RIS Phase for Efficient Base Station Design

TL;DR

This work tackles improving 6G base-station performance by jointly optimizing a movable antenna (MA) and a transmissive RIS (TRIS) operating in the near field. It develops an SNR-based optimization framework with a discrete $b$-bit TRIS phase set and proposes an alternating optimization algorithm to jointly relocate the MA and select TRIS phases, including a quantization function $Q(\cdot)$ and a finite MA search. The analysis shows an upper bound for continuous-phase TRIS and demonstrates that MA repositioning mitigates phase-quantization loss, yielding tangible SNR gains that scale with TRIS size and near-field coupling. The findings support a cost- and energy-efficient pathway to compact 6G BS by exploiting spatial degrees of freedom from MA mobility and low-resolution TRIS phase control. These results inform practical trade-offs between TRIS aperture, phase quantization, and MA mobility for robust near-field wireless design.

Abstract

Movable antennas (MA) and transmissive reconfigurable intelligent surfaces (TRIS) represent two innovative technologies that significantly enhance the flexibility of wireless communication systems. In this paper, we propose a novel and compact base station architecture that synergistically integrates a movable antenna with a transmissive RIS in the near field, enabling joint optimization of antenna positioning and TRIS phase adjustments. The proposed model compensates for phase quantization loss and significantly enhances signal strength, even with low-resolution (1-2 bit) phase shifters. Leveraging this framework, we systematically evaluate system performance as a function of TRIS size and antenna placement. Our results indicate that antenna mobility provides an additional degree of freedom to enhance the desired signal and achieve a higher SNR, particularly when combined with TRIS capabilities. These findings demonstrate that MA-TRIS integration offers a cost-effective and energy-efficient pathway toward compact 6G base stations, combining hardware simplicity with strong performance gains.

Figures (4)

• Figure 1: System model, the suggested compact BS with TRIS and MA, and the user device at the far field.
• Figure 2: Received SNR vs. TRIS size for different quantization bits for the phase-shifters, with and without MA optimization.
• Figure 3: SNR vs. MA-TRIS Distance for an optimized MA.
• Figure 4: Average relative SNR vs. Quantization levels for an optimized MA.