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MIMO-PASS: Uplink and Downlink Transmission via MIMO Pinching-Antenna Systems

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

TL;DR

The paper tackles the challenge of enhancing uplink and downlink throughput in multiuser MIMO by using Pinching-Antenna Systems (PASS) to reconfigure the end-to-end channel via movable pinching elements on dielectric waveguides. It develops a joint hybrid beamforming framework for downlink and a MMSE-based uplink detector, with efficient algorithms based on Fractional Programming, Block Coordinate Descent, and Gauss-Seidel updates, including a low-complexity alternative using Zero-Forcing. The results demonstrate substantial throughput gains over conventional MIMO, massive MIMO, and hybrid architectures, validating PASS as a promising reconfigurable-antenna technology for future wireless systems. The work highlights PASS’s potential to create strong, near-wired LoS-like links by dynamically tuning pinching-element locations, enabling scalable and cost-efficient improvements in indoor and dense deployments.

Abstract

Pinching-antenna systems (PASSs) are a recent flexible-antenna technology that is realized by attaching simple components, referred to as pinching elements, to dielectric waveguides. This work explores the potential of deploying PASS for uplink and downlink transmission in multiuser MIMO settings. For downlink PASS-aided communication, we formulate the optimal hybrid beamforming, in which the digital precoding matrix at the access point and the location of pinching elements on the waveguides are jointly optimized to maximize the achievable weighted sum-rate. Invoking fractional programming and Gauss-Seidel approach, we propose two low-complexity algorithms to iteratively update the precoding matrix and activated locations of the pinching elements. We further study uplink transmission aided by a PASS, where an iterative scheme is designed to address the underlying hybrid multiuser detection problem. We validate the proposed schemes through extensive numerical experiments. The results demonstrate that using a PASS, the throughput in both uplink and downlink is boosted significantly as compared with baseline MIMO architectures, such as massive MIMO~and classical hybrid analog-digital designs. This highlights the great potential of PASSs, making it a promising reconfigurable antenna technology for next-generation wireless systems.

MIMO-PASS: Uplink and Downlink Transmission via MIMO Pinching-Antenna Systems

TL;DR

The paper tackles the challenge of enhancing uplink and downlink throughput in multiuser MIMO by using Pinching-Antenna Systems (PASS) to reconfigure the end-to-end channel via movable pinching elements on dielectric waveguides. It develops a joint hybrid beamforming framework for downlink and a MMSE-based uplink detector, with efficient algorithms based on Fractional Programming, Block Coordinate Descent, and Gauss-Seidel updates, including a low-complexity alternative using Zero-Forcing. The results demonstrate substantial throughput gains over conventional MIMO, massive MIMO, and hybrid architectures, validating PASS as a promising reconfigurable-antenna technology for future wireless systems. The work highlights PASS’s potential to create strong, near-wired LoS-like links by dynamically tuning pinching-element locations, enabling scalable and cost-efficient improvements in indoor and dense deployments.

Abstract

Pinching-antenna systems (PASSs) are a recent flexible-antenna technology that is realized by attaching simple components, referred to as pinching elements, to dielectric waveguides. This work explores the potential of deploying PASS for uplink and downlink transmission in multiuser MIMO settings. For downlink PASS-aided communication, we formulate the optimal hybrid beamforming, in which the digital precoding matrix at the access point and the location of pinching elements on the waveguides are jointly optimized to maximize the achievable weighted sum-rate. Invoking fractional programming and Gauss-Seidel approach, we propose two low-complexity algorithms to iteratively update the precoding matrix and activated locations of the pinching elements. We further study uplink transmission aided by a PASS, where an iterative scheme is designed to address the underlying hybrid multiuser detection problem. We validate the proposed schemes through extensive numerical experiments. The results demonstrate that using a PASS, the throughput in both uplink and downlink is boosted significantly as compared with baseline MIMO architectures, such as massive MIMO~and classical hybrid analog-digital designs. This highlights the great potential of PASSs, making it a promising reconfigurable antenna technology for next-generation wireless systems.

Paper Structure

This paper contains 27 sections, 3 theorems, 74 equations, 5 figures, 3 algorithms.

Table of Contents

  1. Introduction
  2. Reconfigurable Antenna Technologies
  3. Pinching-Antenna Systems
  4. Contributions
  5. System Model
  6. Characterizing Downlink Channel
  7. Characterizing Uplink Channel
  8. Hybrid Beamforming in a Downlink PASS
  9. Joint Digital Precoding and Location Tuning
  10. Downlink Weighted Sum-Rate
  11. Optimal Beamforming Design
  12. Efficient Algorithm for Hybrid Beamforming
  13. Variational Design Problem
  14. Solution via Fractional Programming
  15. Two-tier Iterative Algorithm
  16. ...and 12 more sections

Key Result

Lemma 1

Consider $\mathbf{L} \in \mathbb{R}^{N\times M}$. Let $\tilde{\mathbf{L}}\in \mathbb{R}^{N\times M}$ be another location matrix whose columns are a permutation of the columns of $\mathbf{L}$. Then, for any $\mathbf{W} \in \mathbb{C}^{M\times K}$ we have

Figures (5)

  • Figure 1: Schematic of MIMO-PASS setting: each waveguide is pinched with multiple elements.
  • Figure 2: Convergence of the proposed iterative algorithms for MIMO-PASS uplink and downlink transmission.
  • Figure 3: Weighted sum-rate vs the grid search resolution. Arrows indicate the gain achieved by MIMO-PASS over the baselines.
  • Figure 4: Achievable downlink weighted sum-rate: arrows indicate the gain achieved by MIMO-PASS over the baselines.
  • Figure 5: Weighted uplink sum-rate achieved by MIMO-PASS against the uplink transmit power and number of users.

Theorems & Definitions (7)

  • Remark 1
  • Lemma 1
  • Remark 2
  • Lemma 2: Equality power constraint
  • Lemma 3: Unconstrained Equivalent Problem
  • Remark 3
  • Remark 4