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Joint Antenna Rotation and IRS Beamforming for Multi-User Uplink Communications

Guoying Zhang, Qingqing Wu, Ziyuan Zheng, Qiaoyan Peng, Yanze Zhu, Wen Chen, Penghui Huang

TL;DR

This work tackles angular misalignment and blockage in multi-user uplink communications by jointly optimizing rotatable-antenna (RA) orientations, receive beamforming, and IRS phase shifts in an RA-enabled IRS-assisted system. An alternating optimization (AO) framework is developed, employing projected gradient ascent (PGA) for the 3D RA deflection angles, MMSE-based closed-form receive beamforming, and fractional programming (FP) with Riemannian conjugate gradient (RCG) for IRS phases. The proposed method yields significant sum-rate gains over fixed-antenna and RA-only benchmarks, with larger gains as IRS aperture grows and under moderate transmit power. The results demonstrate that incorporating the RA’s rotational degree of freedom substantially mitigates geometric mismatch in near-field IRS deployments, enabling full realization of IRS gains in practical multi-user uplink settings.

Abstract

Rotatable antenna (RA) enhances wireless coverage through directional gain steering, yet suffers from performance degradation under physical blockages. Intelligent reflecting surface (IRS) establishes reflective paths to bypass obstacles, but suffers from angular mismatch when deployed in the side-lobe region of base station (BS) antennas. To address this issue, we propose a new RA-enabled IRS-assisted multi-user uplink system, in which the BS antennas are capable of flexibly adjusting their 3D orientations to align their boresights with the IRS. We formulate a sum rate maximization problem by jointly optimizing the antenna 3D rotations, receive beamforming and IRS phase shifts. To tackle this non-convex problem, we propose an efficient alternating optimization (AO) algorithm. Specifically, we iteratively update the antenna rotations via projected gradient ascent (PGA), compute the receive beamforming via a closed-form solution, and optimize the IRS phase shifts via fractional programming (FP). Numerical results demonstrate that the proposed system yields significant performance gains over conventional fixed-antenna systems, especially under large angular misalignments.

Joint Antenna Rotation and IRS Beamforming for Multi-User Uplink Communications

TL;DR

This work tackles angular misalignment and blockage in multi-user uplink communications by jointly optimizing rotatable-antenna (RA) orientations, receive beamforming, and IRS phase shifts in an RA-enabled IRS-assisted system. An alternating optimization (AO) framework is developed, employing projected gradient ascent (PGA) for the 3D RA deflection angles, MMSE-based closed-form receive beamforming, and fractional programming (FP) with Riemannian conjugate gradient (RCG) for IRS phases. The proposed method yields significant sum-rate gains over fixed-antenna and RA-only benchmarks, with larger gains as IRS aperture grows and under moderate transmit power. The results demonstrate that incorporating the RA’s rotational degree of freedom substantially mitigates geometric mismatch in near-field IRS deployments, enabling full realization of IRS gains in practical multi-user uplink settings.

Abstract

Rotatable antenna (RA) enhances wireless coverage through directional gain steering, yet suffers from performance degradation under physical blockages. Intelligent reflecting surface (IRS) establishes reflective paths to bypass obstacles, but suffers from angular mismatch when deployed in the side-lobe region of base station (BS) antennas. To address this issue, we propose a new RA-enabled IRS-assisted multi-user uplink system, in which the BS antennas are capable of flexibly adjusting their 3D orientations to align their boresights with the IRS. We formulate a sum rate maximization problem by jointly optimizing the antenna 3D rotations, receive beamforming and IRS phase shifts. To tackle this non-convex problem, we propose an efficient alternating optimization (AO) algorithm. Specifically, we iteratively update the antenna rotations via projected gradient ascent (PGA), compute the receive beamforming via a closed-form solution, and optimize the IRS phase shifts via fractional programming (FP). Numerical results demonstrate that the proposed system yields significant performance gains over conventional fixed-antenna systems, especially under large angular misalignments.
Paper Structure (12 sections, 18 equations, 4 figures, 1 table, 1 algorithm)

This paper contains 12 sections, 18 equations, 4 figures, 1 table, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model and Problem Formulation
  3. RA-Enabled IRS-Assisted Uplink System Model
  4. Channel Model and Signal Model
  5. Problem Formulation
  6. Proposed Solution
  7. BS Antenna Deflection Angle Optimization
  8. Receive Beamforming Optimization
  9. IRS Phase Shift Optimization
  10. Overall Algorithm and Complexity
  11. Simulation Results
  12. Conclusion

Figures (4)

  • Figure 1: An IRS-assisted uplink communication system with RAs.
  • Figure 2: Sum rate vs. users $K$.
  • Figure 3: Sum rate vs. IRS elements $N$.
  • Figure 4: Sum rate vs. power $P_k$.