A generalized framework for the novel center-fed pinching antenna system (C-PASS) is proposed. Within this framework, closed-form expressions for the degree of freedom (DoF) and power scaling law of the proposed C-PASS are first derived. These theoretical results reveal that the achievable DoF scales linearly with the number of input ports, $M$, and the number of receive antennas, $K$. Furthermore, the derived power scaling laws demonstrate that the C-PASS achieves a power gain of order $\mathcal{O}(P_T M)$, where $P_T$ denotes the transmit power. Based on the proposed C-PASS modeling, a sum-rate maximization problem for the joint optimization of transmit and pinching beamforming is then formulated. To solve this highly coupled non-convex problem, an efficient alternating optimization algorithm is developed. More particularly, the transmit precoding and power splitting ratios are updated via derived closed-form solutions, while the pinching antenna positions and radiation coefficients are optimized using block coordinate descent (BCD) methods. Finally, our numerical results reveal that the single-waveguide C-PASS: 1) achieves superior DoF and power scaling laws compared to the single-waveguide PASS; and 2) outperforms the multi-waveguide PASS in high-attenuation regimes, yielding a substantial gain exceeding $10$ dB.

翻译：本文提出了一种新颖的中心馈电夹持天线系统（C-PASS）的通用框架。在此框架内，首先推导了所提C-PASS的自由度（DoF）和功率缩放定律的闭式表达式。这些理论结果表明，可实现的自由度与输入端口数量 $M$ 和接收天线数量 $K$ 呈线性增长。此外，推导出的功率缩放定律表明，C-PASS实现了 $\mathcal{O}(P_T M)$ 量级的功率增益，其中 $P_T$ 表示发射功率。基于所提出的C-PASS建模，随后构建了一个用于联合优化发射与夹持波束成形的和速率最大化问题。为解决这一高度耦合的非凸问题，开发了一种高效的交替优化算法。具体而言，通过推导的闭式解更新发射预编码和功率分配比，同时利用块坐标下降（BCD）方法优化夹持天线位置和辐射系数。最后，数值结果表明，单波导C-PASS：1) 相比单波导PASS实现了更优的自由度和功率缩放定律；2) 在高衰减场景下性能优于多波导PASS，可获得超过 $10$ dB 的显著增益。