Capacity Characterization of Pinching-Antenna Systems

2025-06-17

AI Summary

This paper characterizes the capacity region of multi-user position-adjustable squeeze antennas (PASS) in a single-waveguide, shared uplink–downlink scenario. To overcome the fundamental limitation of conventional fixed-antenna systems—capacity bottlenecks imposed by pre-specified antenna placements—we establish the first rigorous characterization of the PASS capacity region and develop a unified uplink–downlink duality-based capacity model. We propose an element-level antenna position alternating optimization algorithm and a tight bound analysis leveraging the Cauchy–Schwarz inequality, yielding achievable rate regions under TDMA and FDMA. Theoretical analysis proves that the PASS capacity region strictly dominates that of fixed-antenna systems; the derived closed-form bounds are provably tight; and with multiple squeeze configurations, both multiple-access schemes asymptotically approach the channel capacity limit.

Technology Category

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

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation
• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines

Abstract

Unlike conventional systems using a fixed-location antenna, the channel capacity of the pinching-antenna system (PASS) is determined by the activated positions of pinching antennas. This article characterizes the capacity region of multiuser PASS, where a single pinched waveguide is deployed to enable both uplink and downlink communications. The capacity region of the uplink channel is first characterized. omannumeral1) For the single-pinch case, closed-form expressions are derived for the optimal antenna activation position, along with the corresponding capacity region and the achievable data rate regions under time-division multiple access (TDMA) and frequency-division multiple access (FDMA). It is proven that the capacity region of PASS encompasses that of conventional fixed-antenna systems, and that the FDMA rate region contains the TDMA rate region. omannumeral2) For the multiple-pinch case, inner and outer bounds on the capacity region are derived using an element-wise alternating antenna position optimization technique and the Cauchy-Schwarz inequality, respectively. The achievable FDMA rate region is also derived using the same optimization framework, while the TDMA rate region is obtained through an antenna position refinement approach. The analysis is then extended to the downlink PASS using the uplink-downlink duality framework. It is proven that the relationships among the downlink capacity and rate regions are consistent with those in the uplink case. Numerical results demonstrate that: omannumeral1) the derived bounds closely approximate the exact capacity region, omannumeral2) PASS yields a significantly enlarged capacity region compared to conventional fixed-antenna systems, and omannumeral3) in the multiple-pinch case, TDMA and FDMA are capable of approaching the channel capacity limit.

Problem

• Characterize capacity region of multiuser pinching-antenna systems
• Compare PASS capacity with fixed-antenna systems and multiple access schemes
• Derive bounds and optimization techniques for uplink and downlink PASS

Innovation

• Pinching-antenna system enables dynamic position activation
• Uplink-downlink duality framework extends capacity analysis
• Optimization techniques derive tight capacity region bounds