A signal processing-based framework is proposed for detecting random segment failures in segmented waveguide-enabled pinching-antenna systems. To decouple the passively combined uplink signal and to provide per-segment observability, tagged pilots are employed. A simple tag is attached to each segment and is used to apply a known low-rate modulation at the segment feed, which assigns a unique signature to each segment. Based on the tagged-pilot model, a low-complexity per-segment maximum-likelihood (ML) detector is developed for the case in which the pilot length is no smaller than the number of segments. For the case in which the pilot length is smaller than the number of segments, sparsity in the failure-indicator vector is exploited and a compressive sensing-based detector is adopted. Numerical results show that the per-segment detector approaches joint ML performance, while the compressive sensing-based detector achieves reliable detection with a short pilot and can outperform baselines that require much longer pilots.
The pinching-antenna system (PASS) has attracted growing research interest as a reconfigurable-antenna architecture for next-generation networks [1]. PASS, first proposed and prototyped by NTT DOCOMO [2], employs low-loss dielectric waveguides as signal conduits and deploys small dielectric particles, termed pinching antennas (PAs), along the waveguides. Each PA can radiate guided signals into free space and can couple free-space signals back into the waveguide [1]. By adjusting the PA locations, PASS controls the phases and amplitudes of the radiated fields and achieves flexible beampattern shaping. PASS also supports waveguides with long spatial extent. This feature allows PAs to be placed close to users and enables strong line-of-sight (LoS) links, which alleviates large-scale path loss and mitigates blockage effects [3], [4]. In contrast, other reconfigurable-aperture technologies, such as movable antennas, fluid antennas, and reconfigurable intelligent surfaces, typically operate over apertures that span only a few to several tens of wavelengths [5], [6]. This extent is often insufficient at high-frequency bands envisioned for sixth-generation (6G) systems, such as the 7-24 GHz upper mid-bands [7].
Building on these advantages, recent works have optimized the placement of active PAs along a waveguide to enhance communication and sensing performance; see [8], [9] and references therein. Despite this progress, practical deployment C. Ouyang and H. Jiang are with the School of Electronic Engineering and Computer Science, Queen Mary University of London, London, E1 4NS, U.K. (e-mail: {c.ouyang, hao.jiang}@qmul.ac.uk).
Z. Wang and Y. Liu are with the Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong (email: {zhaolin.wang, yuanwei}@hku.hk).
Z. Ding is with the School of Electrical and Electronic Engineering (EEE), Nanyang Technological University, Singapore 639798 (zhiguo.ding@ntu.edu.sg). remains challenging. The main benefit of PASS relies on long dielectric waveguides that sustain stable LoS links. A long monolithic waveguide, however, raises two key concerns. In-waveguide attenuation increases with waveguide length. Maintainability also becomes difficult since a failure can occur at an arbitrary location and repairs may require replacing a large portion of the structure, which increases maintenance cost and limits scalability.
To address these issues, a segmented waveguide-enabled pinching-antenna system (SWAN) was proposed in [10]. SWAN employs multiple short dielectric waveguide segments that are arranged end-to-end without physical interconnection; see Fig. 1. Each segment has an independent feed point for signal injection and extraction. The extracted signals are forwarded to the base station (BS) through wired connections such as optical fiber or low-loss coaxial cables. Signal propagation and maintenance are confined within individual segments, which reduces in-waveguide attenuation and lowers repair cost.
In practice, each segment may experience random failures due to hardware defects, material degradation, or environmental factors. Reliable operation therefore requires timely identification of failed segments. A direct approach inspects segments sequentially, which is costly and time-consuming. This work developes a signal processing-based alternative for SWAN failure detection. We propose a tagged-pilot framework that attaches a simple tag to each segment and applies a known low-rate modulation at the segment feed, which provides a persegment signature after passive combining at the BS. Based on this framework, we develop failure detection methods under two representative regimes. When the pilot length is no smaller than the number of segments, we derive a low-complexity persegment maximum-likelihood (ML) detector that approaches the performance of joint ML detection. When the pilot length is smaller than the number of segments, we exploit sparse failures and design a detector based on compressive sensing. Numerical results validate the effectiveness of the proposed methods in terms of failure detection accuracy.
II. SYSTEM MODEL Consider a communication system where a BS employs a segmented pinched-waveguide structure to serve a singleantenna user, as shown in Fig. 1(a). The user is located in a rectangular service region with side lengths D x and D y along the xand y-axes, respectively. The user location is denoted by u [u x , u y , 0] T . The waveguide extends along the x-axis and covers the full horizontal span of the service region. It is partitioned into M segments, each with length L, so that
T denote the feed-point location of the mth segment, where ψ 1 0 < ψ 2 0 < . . . < ψ M 0 . The feed point is placed at the front-left end of each segment. One PA is deployed on each segment to radiate or capture signals [2]. The PA location on the mth segment (i.e., the mth PA) is denoted by ψ m [ψ m , 0, d] T , and it satisfies
where ∆ > 0 is the mi
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