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Exploiting Segmented Waveguide-Enabled Pinching-Antenna Systems (SWANs) for Uplink Tri-Hybrid Beamforming

Hao Jiang, Chongjun Ouyang, Zhaolin Wang, Yuanwei Liu, Arumugam Nallanathan, Zhiguo Ding, Robert Schober

Abstract

A segmented waveguide-enabled pinching-antenna system (SWAN)-based tri-hybrid beamforming architecture is proposed for uplink multi-user MIMO communications, which jointly optimizes digital, analog, and pinching beamforming. Both fully-connected (FC) and partially-connected (PC) structures between RF chains and segment feed points are considered. For the FC architecture, tri-hybrid beamforming is optimized using the weighted minimum mean-square error (WMMSE) and zero-forcing (ZF) approaches. Specifically, the digital, analog, and pinching beamforming components are optimized via a closed-form solution, Riemannian manifold optimization, and a Gauss-Seidel search, respectively. For the PC architecture, an interleaved topology tailored to the SWAN receiver is proposed, in which segments assigned to each RF chain (sub-array) are interleaved with those from other sub-arrays. Based on this structure, a WMMSE-based tri-hybrid design is developed, in which the Riemannian-manifold update used for the FC structure is replaced by element-wise phase calibration to exploit sparsity in analog beamforming. To gain insight into the performance of the proposed system, the rate-scaling laws with respect to the number of segments are derived for both the FC and PC structures. Our results demonstrate that: i)~SWAN with the proposed tri-hybrid beamforming consistently outperforms conventional hybrid beamforming and conventional pinching-antenna systems with pinching beamforming for both the FC and PC structures; and ii)~the PC structure can strike a good balance between sum rate and energy consumption when the number of segments is large; and iii) the achievable rate does not necessarily increase with the number of segments.

Exploiting Segmented Waveguide-Enabled Pinching-Antenna Systems (SWANs) for Uplink Tri-Hybrid Beamforming

Abstract

A segmented waveguide-enabled pinching-antenna system (SWAN)-based tri-hybrid beamforming architecture is proposed for uplink multi-user MIMO communications, which jointly optimizes digital, analog, and pinching beamforming. Both fully-connected (FC) and partially-connected (PC) structures between RF chains and segment feed points are considered. For the FC architecture, tri-hybrid beamforming is optimized using the weighted minimum mean-square error (WMMSE) and zero-forcing (ZF) approaches. Specifically, the digital, analog, and pinching beamforming components are optimized via a closed-form solution, Riemannian manifold optimization, and a Gauss-Seidel search, respectively. For the PC architecture, an interleaved topology tailored to the SWAN receiver is proposed, in which segments assigned to each RF chain (sub-array) are interleaved with those from other sub-arrays. Based on this structure, a WMMSE-based tri-hybrid design is developed, in which the Riemannian-manifold update used for the FC structure is replaced by element-wise phase calibration to exploit sparsity in analog beamforming. To gain insight into the performance of the proposed system, the rate-scaling laws with respect to the number of segments are derived for both the FC and PC structures. Our results demonstrate that: i)~SWAN with the proposed tri-hybrid beamforming consistently outperforms conventional hybrid beamforming and conventional pinching-antenna systems with pinching beamforming for both the FC and PC structures; and ii)~the PC structure can strike a good balance between sum rate and energy consumption when the number of segments is large; and iii) the achievable rate does not necessarily increase with the number of segments.
Paper Structure (30 sections, 62 equations, 10 figures, 1 table, 3 algorithms)

This paper contains 30 sections, 62 equations, 10 figures, 1 table, 3 algorithms.

Table of Contents

  1. Introduction
  2. Prior Works
  3. Motivations and Contributions
  4. Organization and Notations
  5. System Model
  6. System Model
  7. Problem Formulation
  8. Solutions for SWAN-Based Tri-Hybrid Beamforming for the FC structure
  9. WMMSE-Based Solution to \ref{['pd:uplink_sum_rate']}
  10. Digital Beamforming Optimization
  11. Analog Beamforming Optimization
  12. Pinching Beamforming Optimization
  13. Auxiliary Variable Set Optimization
  14. Zero-Forcing-Based Solution to \ref{['pd:uplink_sum_rate']}
  15. Digital Beamforming Optimization
  16. ...and 15 more sections

Figures (10)

  • Figure 1: Illustration for multi-user uplink tri-hybrid beamforming architecture proposed for SWAN.
  • Figure 2: Illustration of the PC structures: Sequential versus interleaved.
  • Figure 3: Illustration of the convergence behavior at $P=0~\mathrm{dBm}$ and $P=10~\mathrm{dBm}$.
  • Figure 4: Illustration of sum rate versus transmit power.
  • Figure 5: Illustration of sum rate versus the number of RF chains.
  • ...and 5 more figures

Theorems & Definitions (2)

  • Remark 1
  • Remark 2