A pinching antennas (PAs)-aided integrated sensing and multicast communication framework is proposed. In this framework, the communication performance is measured by the multicast rate considering max-min fairness. Moreover, the sensing performance is quantified by the Bayesian Cramér-Rao bound (BCRB), where a Gauss-Hermite quadrature-based approach is proposed to compute the Bayesian Fisher information matrix. Based on these metrics, PA placement is optimized under three criteria: communications-centric (C-C), sensing-centric (S-C), and Pareto-optimal designs. These designs are investigated in two scenarios: the single-PA case and the multi-PA case. 1) For the single-PA case, a closed-form solution is derived for the location of the C-C transmit PA, while the S-C design yields optimal transmit and receive PA placements that are symmetric about the target location. Leveraging this geometric insight, the Pareto-optimal design is solved by enforcing this PA placement symmetry, thereby reducing the joint transmit and receive PA placement to the transmit PA optimization. 2) For the general multi-PA case, the PA placements constitute a highly non-convex optimization problem. To solve this, an element-wise alternating optimization-based method is proposed to sequentially optimize all PA placements for the S-C design, and is further incorporated into an augmented Lagrangian (AL) framework and a rate-profile formulation to solve the C-C and Pareto-optimal design problems, respectively. Numerical results show that: i) PASS substantially outperforms fixed-antenna baselines in both multicast rate and sensing accuracy; ii) the multicasting gain becomes more pronounced as the user density increases; and iii) the sensing accuracy improves with the number of deployed PAs.
Integrated sensing and communications (ISAC) combines dual communication and sensing functionalities over shared wireless resources to improve spectrum utilization and system efficiency [1], [2]. Multiple-input multiple-output (MIMO) technology has been widely regarded as an efficient approach to ISAC, as it leverages spatial diversity and beamforming to simultaneously enhance spectral efficiency and sensing accuracy [3], [4]. However, conventional MIMO architectures remain constrained by their geometrically fixed antenna configurations, which limit their adaptability to dynamic propagation environments. To overcome this limitation, flexibleantenna systems have been proposed as an emerging antenna paradigm that enhance the spatial adaptability of wireless Shan Shan and Yong Li are with the School of Information and Communication Engineering, Beijing University of Posts and Telecommunications, Beijing 100876, China (e-mail: {shan.shan, liyong}@bupt.edu.cn). Chongjun Ouyang is with the School of Electronic Engineering and Computer Science, Queen Mary University of London, London E1 4NS, U.K. (e-mail: c.ouyang@qmul.ac.uk). Xiaohang Yang and Zhiqin Wang are with China Academy of Information and Communications Technology, Beijing 100876, China (e-mail: {yangxiaohang, wangzhiqin}@caict.ac.cn). Yuanwei Liu is with the Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong (e-mail: yuanwei@hku.hk). channels. Representative implementations include movableantenna and fluid-antenna architectures [5], [6]. Movable antennas change their physical positions to modify link geometry, while fluid antennas reshape their electromagnetic aperture through conductive-fluid redistribution. By locally adapting the propagation path, they can mitigate small-scale fading and improve both communication reliability and sensing accuracy in ISAC systems. In addition, reconfigurable intelligent surfaces (RISs) [7] have also been introduced to mitigate propagation blockages. By leveraging controllable phase shifts of numerous passive reflecting elements, RIS technology establishes reliable virtual links between the base station (BS) and sensing targets. However, the effectiveness of movable-antenna and fluid-antenna is generally constrained by limited movement ranges, which restricts their capability in addressing largescale path-loss or line-of-sight (LoS) blockage. Meanwhile, RIS encounters a severe double path-loss effect, especially at higher operating frequencies, which substantially degrades its reflection efficiency.
Recently, the Pinching-Antenna SyStem (PASS) has been experimentally demonstrated as a practical realization of flexibleantennas that addresses the aforementioned limitations [8], [9]. PASS employs a dielectric waveguide as the transmission medium with low in-waveguide propagation loss, and its aperture length spans from a few meters to tens of meters. Along the waveguide, small dielectric elements, termed pinching antennas (PAs), can be dynamically attached or detached, from which radio waves are transmitted or received. A key advantage of PASS for ISAC lies in its scalable waveguide structure, which can be extended to be arbitrarily long. From a communication perspective, this establishes “near-wired” links with strong LoS conditions to individual users. This characteristic effectively mitigates large scale path-loss and avoid LoS blockage [10]. Simultaneously, the long waveguide synthesizes a large effective aperture for sensing, which induces dominant near-field effects that facilitate precise polar domain localization [11].
The above advantages have motivated several early investigations into PASS-enabled communications and sensing. In particular, the authors in [12] provided an informationtheoretic characterization of the achievable rate region for PASS-aided ISAC systems, which revealed a fundamental tradeoff between communication and sensing rates. Extending this analysis, the studies in [13]- [15] investigated the integration of PASS into ISAC systems, where the received signalto-noise ratio (SNR) at the sensing targets was adopted as the performance metric. To obtain a more rigorous measure, subsequent studies adopted the Cramér-Rao bound (CRB), which provides the theoretical lower bound on the estimation error variance of any unbiased estimator [16], [17]. Specifically, the CRB achieved by PASS is first derived in [18] and then compared to that of conventional antennas, while [19] investigated its minimization via a particle swarm optimization (PSO)based algorithm. In parallel, works such as [20]- [22] analyzed round-trip sensing configurations using uniform linear arrays (ULAs) for echo reception. From an architectural perspective, the segmented waveguide system (SWAN) in [23] enhances the degrees of freedom (DoF) available for optimization and characterizes the Pareto fronts for sensing and communication performance. Building on these theoretical foundations, recent wor
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