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Integrated Sensing and Communications for Pinching-Antenna Systems (PASS)
Zheng Zhang, Zhaolin Wang, Xidong Mu, Bingtao He, Jian Chen, Yuanwei Liu
TL;DR
The paper addresses simultaneous communication and sensing with pinching antenna systems. It proposes a separated two-waveguide PASS design and a penalty-based alternating optimization method, with simulations reporting superiority over baseline schemes.
Problem
The paper studies how PASS can provide reliable line-of-sight communication and sensing links while supporting integrated sensing and communication.
Method
A separated two-waveguide design assigns transmission to one waveguide and echo reception to the other, while penalty-based alternating optimization adjusts pinching beamforming.
Results
Simulation results show that the proposed PASS-ISAC framework outperforms baseline schemes, while illumination power increases with the number of activated pinching antennas.
Takeaways & Limitations
Pinching-beamforming reconfiguration supports simultaneous communication and sensing in the proposed PASS framework.
Abstract
from arXiv · showhide
An integrated sensing and communication (ISAC) design for pinching antenna systems (PASS) is proposed, where the pinching antennas are deployed to establish reliable line-of-sight communication and sensing links. More particularly, a separated ISAC design is proposed for the two-waveguide PASS, where one waveguide is used to emit the information-bearing signals for ISAC transmission while the other waveguide is used to receive the reflected echo signals. Based on this framework, a penalty-based alternating optimization algorithm is proposed to maximize the illumination power as well as ensure the communication quality-of-service requirement. Numerical results demonstrate that the proposed PASS-ISAC scheme outperforms the conventional antenna scheme.
I. INTRODUCTION
The paper proposes a separated ISAC design for PASS that uses two waveguides to support communication and sensing. It optimizes pinching-antenna positions and beamforming to maximize target illumination while meeting communication QoS.
- Pinching antennas provide flexible repositioning, wide-range mobility, and potentially large apertures for favorable line-of-sight and nearfield links.
- The optimization maximizes target illumination power under a transmit-power budget and communication quality-of-service requirement.
- The design targets simultaneous communication and sensing using a dual-function base station, a single-antenna user, and a point-like target.
- A two-waveguide PASS separates functions: one waveguide transmits information-bearing signals, while the other receives target echoes for parameter estimation.
- The model uses 3D waveguide geometry, spherical-wave nearfield channels, and equal power allocation for the pinching antennas.
B. Signal Model
The signal model defines pinching beamforming through antenna-position-dependent channel reconfiguration. It assumes continuous activation, allowing antennas to be placed anywhere on the dielectric waveguide subject to minimum spacing.
- B. Signal Model: Pinching beamforming captures how antenna positions jointly affect free-space and in-waveguide channels for the user and sensing target.
- B. Signal Model: Under continuous activation, pinching antennas can be activated at any waveguide position.
- B. Signal Model: Adjacent pinching antennas must maintain a minimum separation distance Δx.
1) Communication Performance Metric:
The communication performance metric is based on the received user signal and achievable rate, while sensing performance is characterized by target illumination power.
- 1) Communication Performance Metric:: The communication metric derives the user’s achievable rate from the received signal, including additive white Gaussian noise.
- 2) Sensing Performance Metric:: Illumination power measures the received sensing signal power at the target.
C. Problem Formulation
The formulation maximizes target illumination power while meeting the communication user's QoS requirement under a transmit-power budget. Its quadratic objective and coupled variables make the problem challenging to solve.
- The optimization maximizes illumination power at the target subject to a transmit-power budget and the communication user's QoS requirement.
- The problem is difficult because its objective function is quadratic and its variables are coupled.
III. PINCHING BEAMFORMING OPTIMIZATION
The proposed penalty-based alternating optimization reformulates the coupled design using auxiliary beamforming variables, penalty terms, semidefinite relaxation, and rank-one recovery. It alternates beamforming and antenna-position updates while preserving equivalence to the original problem.
- A penalty-based alternating optimization framework handles the coupled variables by optimizing pinching-antenna positions element-wise and alternating them with auxiliary beamforming variables.
- The reformulation replaces beamforming expressions with auxiliary variables and moves their equality constraints into the objective as penalty terms.
- Semidefinite relaxation converts the quadratic objective and constraints into a lifted problem involving matrix beamforming variables.
- An iterative difference-of-convex procedure recovers rank-one beamforming solutions by repeatedly solving a convex problem and updating dominant eigenvectors.
2) Inner layer iteration—subproblem with respect to
With the beamforming variables fixed, the inner-layer position subproblem separates across pinching antennas in the objective but remains coupled through a constraint. Each position is therefore optimized using a low-complexity one-dimensional search.
- The position variables are separated in the objective but coupled in a constraint, motivating element-wise optimization.
- Each pinching-antenna position is updated through a low-complexity one-dimensional search with the other positions fixed.
3) Outer layer iteration:
The outer penalty-based alternating optimization iteratively updates beamforming and antenna positions, then increases the penalty parameter until convergence. The algorithm is stated to converge at least to a stationary-point solution, with complexity dominated by semidefinite programs and one-dimensional search.
- The penalty parameter is updated using an iteration coefficient satisfying 0 < c̄2 < 1.
- The penalty-based alternating optimization algorithm is assured to converge at least to a stationary-point solution.
- The algorithm repeatedly updates auxiliary beamforming variables with Algorithm 1 and antenna positions through element-wise optimization until the objective converges.
- Algorithm 2's computational complexity mainly depends on solving the semidefinite programs and performing the one-dimensional exhaustive search, whose quantization-bit count is denoted by Q̄.
IV. NUMERICAL RESULTS
The simulations evaluate PASS-ISAC under a 3D setup and compare pinching-antenna designs with conventional and fixed baselines. Results show that illumination depends on antenna count, power allocation, waveguide rotation, and height.
- The numerical evaluation uses a 3D topological network with a dielectric waveguide in the x-o-z plane and user and target positions in a square x-o-y region.The default parameters include σ2 = −105 dBm, f = 28 GHz, d = 10 m, and rs = 30 m.
- The comparison includes conventional antennas with one RF chain and analog phase shifters, alongside fixed pinching antennas.The conventional array uses antenna spacing of λ/2, while fixed pinching antennas remain uniformly distributed along the waveguide.
- Pinching antennas achieve the highest illumination power among the evaluated baseline schemes.Their repositioning attenuates large-scale path loss and provides additional spatial degrees of freedom; semi-continuous activation also outperforms conventional antennas by distributing antennas across the communication/sensing area.
- Increasing the number of activated pinching antennas raises illumination power by improving beam resolution and reducing power leakage.The proportional power allocation model is slightly inferior to equal power allocation in the reported comparison.
- Illumination power first increases and then decreases with waveguide rotation, reaching its maximum at 60° when the target lies underneath the waveguide.Further rotation increases the target-to-antenna distance, while increasing waveguide height decreases illumination power by increasing average distances to the user and target.
V. CONCLUSION
The paper proposes PASS-ISAC with pinching beamforming for simultaneous communication and sensing. Its separated two-waveguide design and penalty-based alternating optimization maximize target illumination while guaranteeing communication QoS, and simulations show superiority over baseline schemes.
- The proposed PASS-ISAC framework uses pinching beamforming for simultaneous communication and sensing.
- A separated two-waveguide design assigns one waveguide to transmission and the other to reflected-echo reception.
- A penalty-based alternating optimization algorithm maximizes target illumination while guaranteeing the communication user’s QoS requirement.
- Simulation results verify that PASS-ISAC outperforms the evaluated baseline schemes.