Rotatable Antenna-Enhanced Cell-Free Communication

2025-12-04

AI Summary

This paper addresses the downlink sum-rate maximization problem in cell-free massive MIMO systems empowered by mechanically rotatable antennas, jointly optimizing access point (AP)–user association and three-dimensional beam pointing. It is the first work to incorporate mechanically steerable antennas into the cell-free architecture, thereby enhancing spatial degrees of freedom through dynamic beam steering and multi-AP cooperative transmission. To tackle the non-convex beamforming subproblem, the proposed method leverages fractional programming combined with successive convex approximation (SCA); a two-stage algorithm is further designed to handle AP–user association. Simulation results demonstrate that the proposed scheme significantly outperforms conventional benchmarks—including fixed-beam, static-association, and fully digital precoding schemes—in terms of sum rate. The results validate both the feasibility and superiority of mechanical beam control in cell-free wireless systems.

Technology Category

• Multiagent Systems: Mechanism Design
• Search and Optimization: Mixed Discrete/Continuous Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems

Application Category

• User Modeling, Personalization and Recommendation: Federated recommendation systems and personalization
• Systems and Infrastructure for Web, Mobile and WoT: Applied ML and AI for Web-based mobile applications
• Security and Privacy: Large-scale security measurements

Abstract

Rotatable antenna (RA) is a promising technology that can exploit new spatial degrees-of-freedom (DoFs) by flexibly adjusting the three-dimensional (3D) boresight direction of antennas. In this letter, we investigate an RA-enhanced cell-free system for downlink transmission, where multiple RA-equipped access points (APs) cooperatively serve multiple single-antenna users over the same time-frequency resource. Specifically, we aim to maximize the sum rate of all users by jointly optimizing the AP-user associations and the RA boresight directions. Accordingly, we propose a two-stage strategy to solve the AP-user association problem, and then employ fractional programming (FP) and successive convex approximation (SCA) techniques to optimize the RA boresight directions. Numerical results demonstrate that the proposed RA-enhanced cell-free system significantly outperforms various benchmark schemes.

Problem

• Maximizes sum rate in RA-enhanced cell-free downlink transmission
• Jointly optimizes AP-user associations and RA boresight directions
• Proposes a two-stage strategy with FP and SCA techniques

Innovation

• Rotatable antennas enable flexible 3D beam direction adjustment
• Joint optimization of AP-user associations and antenna orientations
• Fractional programming and convex approximation for beam direction optimization