Rate Maximization for Downlink Pinching-Antenna Systems
Yanqing Xu, Zhiguo Ding, George K. Karagiannidis
TL;DR
This paper tackles downlink rate maximization for a novel pinching-antenna system, where multiple low-cost antennas are positioned along a dielectric waveguide to serve a single user. It introduces a relaxed, two-stage optimization: first, maximize the sum of reciprocals of distances to mitigate large-scale path loss under spacing constraints, yielding a closed-form, unimodal solution $\tilde{x}_1^* = x_m - \frac{N-1}{2} \Delta$ and antenna locations $\tilde{\boldsymbol{\psi}}_n^{\rm Pin}$; second, refine antenna positions on the wavelength scale to satisfy phase alignment constraints via sequential, local phase-difference minimization. The method balances path-loss mitigation with constructive signal combination, achieving near-optimal performance relative to exhaustive search and outperforming conventional fixed-antenna systems. Simulation results confirm the advantages of pinching-antenna deployments and demonstrate the practical viability of the proposed algorithm for flexible, low-cost downlink optimization in waveguide-based setups.
Abstract
In this letter, we consider a new type of flexible-antenna system, termed pinching-antenna, where multiple low-cost pinching antennas, realized by activating small dielectric particles on a dielectric waveguide, are jointly used to serve a single-antenna user. Our goal is to maximize the downlink transmission rate by optimizing the locations of the pinching antennas. However, these locations affect both the path losses and the phase shifts of the user's effective channel gain, making the problem challenging to solve. To address this challenge and solve the problem in a low complexity manner, a relaxed optimization problem is developed that minimizes the impact of path loss while ensuring that the received signals at the user are constructive. This approach leads to a two-stage algorithm: in the first stage, the locations of the pinching antennas are optimized to minimize the large-scale path loss; in the second stage, the antenna locations are refined to maximize the received signal strength. Simulation results show that pinching-antenna systems significantly outperform conventional fixed-location antenna systems, and the proposed algorithm achieves nearly the same performance as the highly complex exhaustive search-based benchmark.