Pinching antenna systems (PASS) have recently emerged as a promising architecture for high-frequency wireless communications. In this letter, we investigate localization in PASS by jointly exploiting the received signal amplitude and phase information, unlike recent works that consider only the amplitude information. A complex baseband signal model is formulated to capture free-space path loss, waveguide attenuation, and distance-dependent phase rotation between the user and each pinching antenna. Using this model, we derive the Fisher information matrix (FIM) with respect to the user location and obtain closed-form expressions for the Cramer-Rao lower bound (CRLB) and the position error bound (PEB). A maximum likelihood (ML) estimator that jointly considers the received signal amplitude and phase is developed to estimate the unknown user location. Given the non-convexity of the estimation problem, a two-stage solution combining coarse grid search and Levenberg-Marquardt refinement is proposed. Numerical results demonstrate that the proposed phase-aware estimator outperforms existing amplitude-only method in terms of positioning accuracy.

翻译：夹持天线系统（PASS）作为一种有前景的高频无线通信架构，近年来备受关注。与近期仅利用接收信号幅度信息的研究不同，本文通过联合利用接收信号的幅度与相位信息，对PASS中的定位问题展开研究。我们建立了一个复基带信号模型，以捕捉用户与每个夹持天线之间的自由空间路径损耗、波导衰减以及距离相关的相位旋转。基于该模型，我们推导了关于用户位置的费舍尔信息矩阵（FIM），并得到了克拉美-罗下界（CRLB）与位置误差界（PEB）的闭式表达式。为了估计未知的用户位置，我们开发了一种联合考虑接收信号幅度与相位的最大似然（ML）估计器。针对该估计问题的非凸性，提出了一种结合粗粒度网格搜索与Levenberg-Marquardt精细化的两阶段求解方案。数值结果表明，所提出的基于相位的估计器在定位精度方面优于现有的仅利用幅度信息的方法。