Performance Analysis of XL-MIMO With Rotary and Movable Antennas for High-Speed Railway

The rotary and movable antennas (ROMA) technology is efficient in enhancing wireless network capacity by adjusting both the antenna spacing and three-dimensional (3D) rotation of antenna surfaces, based on the spatial distribution of users and channel statistics. Applying ROMA to high-speed rail (HSR) wireless communications can significantly improve system performance in terms of array gain and spatial multiplexing. However, the rapidly changing channel conditions in HSR scenarios present challenges for ROMA configuration. In this correspondence, we propose an analytical framework for configuring ROMA-based extremely large-scale multiple-input-multiple-output (XL-MIMO) systems in HSR scenarios based on spatial correlation. First, we develop a localization model based on a mobility-aware near-field beam training algorithm to determine the real-time position of the train relay antennas. Next, we derive the expression for channel orthogonality and antenna spacing based on the spatial correlation matrix, and obtain the optimal antenna spacing when the transceiver arrays are aligned in parallel. Moreover, we propose an optimization algorithm for the rotation angle of the transceiver arrays, leveraging the differential evolution method, to determine the optimal angles. Finally, numerical results are provided to validate the computational results and optimization algorithm.