The novel architecture of the center-fed pinching antenna system (C-PASS) is investigated, where the waveguide-fed signal is divided into two propagation directions through controllable power splitting. By doing so, a doubled degree of freedom (DoF) is achieved compared to conventional PASS. Based on the new designed basic signal model of C-PASS, three practical operating protocols for C-PASS are proposed, namely power splitting (PS), direction switching (DS), and time switching (TS). Then, the sum-rate maximization problem for the joint optimization of transmit and pinching beamforming is formulated for each of the proposed protocols. 1) For PS, the highly coupled non-convex problem is first transformed into a tractable form via the weighted minimum mean square error reformulation and solved using the alternating optimization framework; 2) For DS, the above approach is subsequently extended to solve the mixed-integer constraints inherent for DS via the penalty-based algorithm; 3) For TS, the optimization problem can be decomposed into two subproblems and solved using the similar iterative techniques, while its optimal time allocation ratio is derived in closed form. Finally, numerical results reveal that TS is superior in the low-power regime, while PS and DS achieve significantly higher rates in the high-power regime due to the enhanced DoF.

翻译：本文研究了中心馈电夹持天线系统（C-PASS）的新型架构，其中波导馈送的信号通过可控功率分配被分成两个传播方向。通过这种方式，与传统PASS相比，实现了加倍的自由度（DoF）。基于新设计的C-PASS基本信号模型，提出了三种实用的C-PASS操作协议，即功率分配（PS）、方向切换（DS）和时间切换（TS）。随后，针对每种提出的协议，构建了发射与夹持波束成形联合优化的和速率最大化问题。1）对于PS，首先通过加权最小均方误差重构将高度耦合的非凸问题转化为易处理形式，并利用交替优化框架求解；2）对于DS，随后将上述方法扩展，通过基于惩罚的算法解决DS固有的混合整数约束；3）对于TS，优化问题可分解为两个子问题，并使用类似的迭代技术求解，同时其最优时间分配比例以闭合形式导出。最后，数值结果表明，在低功率区域TS更优，而在高功率区域，由于增强的DoF，PS和DS实现了显著更高的速率。