Distributed Antenna Systems (DASs) employ multiple antenna arrays in remote radio units to achieve highly directional transmission and provide great coverage performance for future-generation networks. However, the utilization of active antenna arrays results in a significant increase in hardware costs and power consumption for DAS. To address these issues, integrating DAS with Reconfigurable Intelligent Surfaces (RIS) offers a viable approach to ensure transmission performance while maintaining low hardware costs and power consumption. To incorporate the merits of RIS into the DAS from practical consideration, a novel architecture of ``Reconfigurable Distributed Antennas and Reflecting Surfaces (RDARS)'' is proposed in this paper. Specifically, based on the design of the additional direct-through state together with the existing high-quality fronthaul link, any element of the RDARS can be dynamically programmed to connect with the base station (BS) via fibers and perform the connected mode as remote distributed antennas of the BS to receive or transmit signals. Additionally, RDARS also inherits the low-cost and low-energy-consumption benefits of fully passive RISs by default configuring the elements as passive to perform the reflection mode. As a result, RDARS offers flexible control over the trade-off between distribution gain and reflection gain to enhance performance. The ergodic achievable rate under the RDARS architecture is analyzed and closed-form expression with meaningful insights is derived. The theoretical analysis and simulation results prove that the RDARS achieves a higher achievable rate than both DAS and RIS. A RDARS prototype with 256 elements is built for real experiments which shows that the RDARS-aided system can achieve an additional 21% and 170% throughput improvement over DAS and RIS-aided systems, respectively.

翻译：分布式天线系统（DAS）通过在远端射频单元部署多组天线阵列，可实现高度定向传输并为下一代网络提供优异的覆盖性能。然而，有源天线阵列的使用导致DAS的硬件成本和功耗显著增加。为解决这些问题，将DAS与可重构智能表面（RIS）相结合，提供了一种在保持低硬件成本和功耗的同时确保传输性能的可行方案。为从实际应用角度将RIS的优势融入DAS，本文提出一种名为"可重构分布式天线与反射表面（RDARS）"的新型架构。具体而言，基于附加的直通状态设计与现有高质量前传链路，RDARS的任意单元均可动态编程以通过光纤与基站（BS）连接，作为BS的远程分布式天线执行连接模式以接收或发射信号。此外，RDARS默认将单元配置为无源状态以执行反射模式，从而继承了全无源RIS的低成本与低能耗优势。因此，RDARS能够灵活控制分布增益与反射增益之间的权衡以提升性能。本文分析了RDARS架构下的遍历可达速率，推导了具有深刻意义的闭式表达式。理论分析与仿真结果证明，RDARS的可达速率优于DAS和RIS。我们构建了包含256个单元的RDARS原型并进行实际实验，结果显示：相较于DAS辅助系统和RIS辅助系统，RDARS辅助系统可分别实现21%和170%的额外吞吐量提升。