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Downlink Beamforming with Pinching-Antenna Assisted MIMO Systems

Ali Bereyhi, Saba Asaad, Chongjun Ouyang, Zhiguo Ding, H. Vincent Poor

TL;DR

This work tackles downlink beamforming in a multiuser MIMO system aided by pinching-antenna systems (PAS), where movable pinching elements along dielectric waveguides reconfigure the end-to-end channel. The authors formulate a joint design problem for the digital precoder and pinching locations to maximize a weighted sum-rate under a power constraint, and solve it using a variational fractional programming framework with a two-tier block coordinate descent algorithm. The approach combines a Lagrange-like dual transform, a quadratic transform for fractions, and a Gauss-Seidel style per-location search, ensuring convergence and tractable complexity. Numerical results show PAS significantly outperforms fixed-location antenna baselines, achieving substantial throughput gains and indicating PAS potential as a practical enabling technology for next-generation wireless networks.

Abstract

Pinching antennas have been recently proposed as a promising flexible-antenna technology, which can be implemented by attaching low-cost pinching elements to dielectric waveguides. This work explores the potential of employing pinching antenna systems (PASs) for downlink transmission in a multiuser MIMO setting. We consider the problem of hybrid beamforming, where the digital precoder at the access point and the activated locations of the pinching elements are jointly optimized to maximize the achievable weighted sum-rate. Invoking fractional programming, a novel low-complexity algorithm is developed to iteratively update the precoding matrix and the locations of the pinching antennas. We validate the proposed scheme through extensive numerical experiments. Our investigations demonstrate that using PAS the system throughput can be significantly boosted as compared with the conventional fixed-location antenna systems, enlightening the potential of PAS as an enabling candidate for next-generation wireless networks.

Downlink Beamforming with Pinching-Antenna Assisted MIMO Systems

TL;DR

This work tackles downlink beamforming in a multiuser MIMO system aided by pinching-antenna systems (PAS), where movable pinching elements along dielectric waveguides reconfigure the end-to-end channel. The authors formulate a joint design problem for the digital precoder and pinching locations to maximize a weighted sum-rate under a power constraint, and solve it using a variational fractional programming framework with a two-tier block coordinate descent algorithm. The approach combines a Lagrange-like dual transform, a quadratic transform for fractions, and a Gauss-Seidel style per-location search, ensuring convergence and tractable complexity. Numerical results show PAS significantly outperforms fixed-location antenna baselines, achieving substantial throughput gains and indicating PAS potential as a practical enabling technology for next-generation wireless networks.

Abstract

Pinching antennas have been recently proposed as a promising flexible-antenna technology, which can be implemented by attaching low-cost pinching elements to dielectric waveguides. This work explores the potential of employing pinching antenna systems (PASs) for downlink transmission in a multiuser MIMO setting. We consider the problem of hybrid beamforming, where the digital precoder at the access point and the activated locations of the pinching elements are jointly optimized to maximize the achievable weighted sum-rate. Invoking fractional programming, a novel low-complexity algorithm is developed to iteratively update the precoding matrix and the locations of the pinching antennas. We validate the proposed scheme through extensive numerical experiments. Our investigations demonstrate that using PAS the system throughput can be significantly boosted as compared with the conventional fixed-location antenna systems, enlightening the potential of PAS as an enabling candidate for next-generation wireless networks.

Paper Structure

This paper contains 13 sections, 2 theorems, 32 equations, 3 figures, 1 algorithm.

Table of Contents

  1. Introduction
  2. Pinching-Antenna Systems
  3. Contributions
  4. System Model and Problem Formulation
  5. Characterizing End-to-End Channel
  6. Downlink Beamforming
  7. Hybrid Beamforming Design
  8. Optimal Beamforming Design
  9. Variational Solution via Fractional Programming
  10. Two-tier Iterative Algorithm
  11. Overall Algorithm, Convergence, and Complexity
  12. Numerical Investigations
  13. Conclusion

Key Result

Lemma 1

The optimal solution to the problem eq:optim satisfies the power constraint with equality, i.e., $\mathrm{tr}\left\lbrace \mathbf{W}_{\star}^{\mathsf{H}} \mathbf{W}_{\star} \right\rbrace = P$, for any $\mathbf{W}_\star$ that is a solution to eq:optim.

Figures (3)

  • Figure 1: Illustration of the system configuration: AP is equipped by multiple waveguides each pinched with an element.
  • Figure 2: Weighted sum-rate achieved by PAS. Arrows indicate the gain achieved by the proposed scheme over the fixed-antenna system.
  • Figure 3: Convergence of the proposed algorithm for different choices of $M$. Here, $P = 20$ dBm, $D=30$ m, and $K=4$.

Theorems & Definitions (4)

  • Remark 1
  • Lemma 1
  • Lemma 2
  • Remark 2