Fundamental limit of Sum Capacity in Pinching Antenna Assisted Multiple Access Channel

2025-08-07

AI Summary

This work investigates fundamental limits of dynamic clamping beamforming and sum capacity in clamped-antenna-assisted multiple-access channels. For a reconfigurable channel realized via tunable-position clamped antennas on a dielectric waveguide, we propose a time-division alternating transmission strategy among users—obviating the need for NOMA—and rigorously prove its asymptotic optimality under large user numbers. We derive a closed-form upper bound on sum capacity and a lower bound on sum rate for finite users. Numerical results demonstrate that the proposed dynamic beamforming scheme significantly enhances system capacity under average power constraints while circumventing the complex interference management inherent to NOMA. The core contribution lies in uncovering a novel fundamental limit on joint optimization of physical-layer channel reconfiguration and multiuser scheduling, thereby establishing a theoretical foundation for ultra-low-overhead reconfigurable wireless access.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Mixed Discrete/Continuous Search
• Multiagent Systems: Mechanism Design

Application Category

• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs
• Responsible Web: Machine-in-the-loop, human agency and autonomy

Abstract

Pinching antenna systems (PASSs) have recently shown their promising ability to flexibly reconfigure wireless channels via dynamically adjusting the positions of pinching antennas over a dielectric waveguide, termed as pinching beamforming. This paper studies the fundamental limit of the sum capacity for a PASSassisted multiple access channel, in which multiple users transmit individual messages to a BS under the average power constraint. To this end, we consider a dynamic pinching beamforming setup, where multiple pinching beamforming vectors are employed in a transmission period and the capacity-achieving non-orthogonal multiple access (NOMA) based transmission scheme is considered. For the ideal case with an asymptotically large number of pinching beamforming vectors, we unveil that the optimal transmission scheme is alternating transmission among each user with its channel power gain maximized by dynamic pinching beamforming, which implies that the NOMA-based transmission scheme is not needed. The corresponding sum-rate is derived in closed-form expression, which serves as the upper bound of the sum-capacity. Inspired by this result, a lower bound of the sum-rate under an arbitrarily finite number of pinching beamforming vectors is obtained. Numerical results validate our theoretical findings and illustrate the practical significance of using dynamic pinching beamforming to improve the sum capacity.

Problem

• Study sum capacity limit in PASS-assisted multiple access channels
• Analyze dynamic pinching beamforming impact on user transmission
• Derive upper and lower bounds for sum-rate capacity

Innovation

• Dynamic pinching beamforming reconfigures wireless channels
• Alternating transmission maximizes user channel power gain
• Closed-form sum-rate expression provides capacity upper bound