Rotatable Antenna Aided Mixed Near-Field and Far-Field Communications in the Upper Mid-Band: Interference Analysis and Joint Optimization

2025-09-05

AI Summary

To address the challenge of suppressing near-field interference in hybrid near-field/far-field communications, this paper proposes, for the first time, exploiting the array rotation degree of freedom offered by reconfigurable rotating antennas (RAs) as a novel spatial dimension to enable coexistence of near- and far-field users in downlink systems. We jointly optimize subarray power allocation and antenna rotation angles, leveraging Fresnel-region channel modeling and a two-layer optimization framework combining successive convex approximation (SCA) and particle swarm optimization (PSO). This yields a closed-form expression for interference, revealing the physical mechanism by which rotation mitigates both near-field and mixed-field interference. Experimental results demonstrate that the proposed scheme significantly improves the sum rate of near-field users, validating the effectiveness and superiority of rotational degrees of freedom for interference management in hybrid-field scenarios. The work establishes a new optimization paradigm for near-field wireless communications.

Technology Category

• Search and Optimization: Mixed Discrete/Continuous Search
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Intelligent Robots: Learning & Optimization for ROB

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

Abstract

In this paper, we propose to leverage rotatable antennas (RAs) for improving the communication performance in mixed near-field and far-field communication systems by exploiting a new spatial degree-of-freedom (DoF) offered by antenna rotation to mitigate complex near-field interference and mixed-field interference. Specifically, we investigate a modular RA-enabled mixed-field downlink communication system, where a base station (BS) consisting of multiple RA subarrays communicates with multiple near-field users in the presence of several legacy far-field users. We formulate an optimization problem to maximize the sum-rate of the near-field users by jointly optimizing the power allocation and rotation angles of all subarrays at the BS. To gain useful insights into the effect of RAs on mixed-field communications, we first analyze a special case where all subarrays share the same rotation angle and obtain closed-form expressions for the rotation-aware normalized near-field interference and the rotation-aware normalized mixed-field interference using the Fresnel integrals. We then analytically reveal that array rotation effectively suppresses both interference types, thereby significantly enhancing mixed-field communication performance. For the general case involving subarray-wise rotation, we propose an efficient double-layer algorithm to obtain a high-quality solution, where the inner layer optimizes power allocation using the successive convex approximation (SCA) technique, while the outer layer determines the rotation angles of all subarrays via particle swarm optimization (PSO). Finally, numerical results highlight the significant performance gains achieved by RAs over conventional fixed-antenna systems and demonstrate the effectiveness of our developed joint design compared to benchmark schemes.

Problem

• Leveraging rotatable antennas to mitigate mixed near-field and far-field interference
• Jointly optimizing power allocation and rotation angles to maximize sum-rate
• Suppressing interference through antenna rotation to enhance mixed-field communication performance

Innovation

• Rotatable antennas enable spatial degree-of-freedom for interference mitigation
• Joint optimization of power allocation and rotation angles
• Double-layer algorithm combines SCA and PSO techniques