In this paper, we propose a distributed flexible coupler (FC) array to enhance communication performance with low hardware cost. At each FC antenna, there is one fixed-position active antenna and multiple passive couplers that can move within a designated region around the active antenna. Moreover, each FC antenna is equipped with a local processing unit (LPU). All LPUs exchange signals with a central processing unit (CPU) for joint signal processing. We study an FC-aided multiuser multiple-input multiple-output (MIMO) system, where an FC array base station (BS) is deployed to enhance the downlink communication between the BS and multiple single-antenna users. We formulate optimization problems to maximize the achievable sum rate of users by jointly optimizing the coupler positions and digital beamforming, subject to movement constraints on the coupler positions and the transmit power constraint. To address the resulting nonconvex optimization problem, the digital beamforming is expressed as a function of the FC position vectors, which are then optimized using the proposed distributed coupler position optimization algorithm. Considering a structured time domain pattern of pilots and coupler positions, pilot-assisted centralized and distributed channel estimation algorithms are designed under the FC array architecture. Simulation results demonstrate that the distributed FC array achieves substantial rate gains over conventional benchmarks in multiuser systems without moving active antennas, and approaches the performance of fully active arrays while significantly reducing hardware cost and power consumption. Moreover, the proposed channel estimation algorithms outperform the benchmark schemes in terms of both pilot overhead and channel reconstruction accuracy.

翻译：本文提出一种分布式柔性耦合器阵列，以较低硬件成本提升通信性能。每个柔性耦合器天线包含一个固定位置的有源天线和多个可在有源天线周围指定区域内移动的无源耦合器。此外，每个柔性耦合器天线配备本地处理单元，所有本地处理单元与中央处理单元进行信号交互以实现联合信号处理。我们研究一种柔性耦合器辅助的多用户多输入多输出系统，其中部署柔性耦合器阵列基站以增强基站与多个单天线用户间的下行链路通信。我们构建了优化问题，在耦合器位置移动约束和发射功率约束条件下，通过联合优化耦合器位置与数字波束成形来最大化用户可达和速率。针对由此产生的非凸优化问题，将数字波束成形表达为柔性耦合器位置向量的函数，进而采用所提出的分布式耦合器位置优化算法进行位置优化。考虑导频与耦合器位置的结构化时域模式，在柔性耦合器阵列架构下设计了导频辅助的集中式与分布式信道估计算法。仿真结果表明：在不移动有源天线的多用户系统中，分布式柔性耦合器阵列相比传统基准方案实现了显著的速率增益，且能以显著降低的硬件成本与功耗逼近全有源阵列的性能。此外，所提出的信道估计算法在导频开销与信道重构精度方面均优于基准方案。