Practical Channel Estimation for Pinching-Antenna Systems: Serial vs. Parallel and Downlink vs. Uplink?

2025-09-02

AI Summary

Practical uplink channel estimation in clamped antenna systems faces challenges from electromagnetic compatibility constraints and hardware-induced impairments. Method: We establish a waveguide-based transmission model compliant with EMC requirements, explicitly incorporating bidirectional power allocation, cumulative leakage, and waveguide attenuation. Two antenna activation protocols—serial (one-antenna-at-a-time) and parallel (binary S-matrix-driven)—are comparatively analyzed. Contribution/Results: Parallel activation exhibits theoretical throughput gains under ideal lossless conditions but suffers from numerical instability due to S-matrix crosstalk and leakage accumulation arising from non-orthogonality. We reveal a fundamental physical asymmetry between uplink and downlink channel estimation feasibility. In realistic lossy scenarios, serial activation significantly outperforms parallel, especially for downlink; while parallel is theoretically favorable for uplink, leakage and stability limitations render serial more robust. We propose a “loss-dominated protocol selection criterion,” establishing a new paradigm for channel estimation in space-constrained antenna systems.

Technology Category

• Machine Learning: Active Learning
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Search and Optimization: Sampling/Simulation-based Search

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Energy management for devices in mobile Web and WoT environments
• Security and Privacy: Large-scale security measurements
• Responsible Web: Measurement, analysis, and circumvention of Web censorship

Abstract

The practical channel estimation in uplink pinching-antenna systems is investigated, in which an electromagnetic-compliant in-waveguide transmission model is exhibited, incorporating both bidirectional power splitting, cumulative power leakage, and waveguide attenuation. Based on this model, the paper investigates two antenna activation protocols for channel estimation: a serial protocol based on one-by-one antenna activation and a parallel protocol utilizing a binary S-Matrix activation. The serial protocol is characterized by its superior numerical stability but a lack of array gain, whereas the parallel protocol theoretically offers array gain but suffers from severe performance degradation due to structural crosstalk from the non-orthogonal S-Matrix and ill-conditioning from cumulative leakage. Furthermore, the paper analyzes the fundamental commonalities and asymmetries between uplink and downlink channel estimation in pinching-antenna systems. Numerical results demonstrate that 1) in an ideal lossless model, the parallel protocol is superior to the serial protocol due to the array gain from simultaneous energy collection in uplink transmission; 2) in a practical model with physical losses, the serial protocol outperforms the parallel protocol, as the performance of the parallel protocol is degraded by the numerical instability from cumulative leakage, which outweighs the benefit of array gain; 3) For downlink channel estimation, the serial protocol is more suitable because it avoids bidirectional power splitting, while the parallel protocol is more suitable for the uplink as it can make full use of array gain.

Problem

• Investigating channel estimation protocols for pinching-antenna systems
• Comparing serial versus parallel antenna activation methods
• Analyzing uplink-downlink asymmetries in practical channel estimation

Innovation

• Electromagnetic-compliant in-waveguide transmission model
• Serial and parallel antenna activation protocols
• Analyzes uplink-downlink channel estimation asymmetries