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中部署多个天线阵列，能够实现高方向性传输，并为未来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法。为了实际考虑中将RIS的优势融入DAS，本文提出了一种新型架构——"可重构分布式天线与反射表面（RDARS）"。具体而言，基于额外直通状态的设计以及现有的高质量前传链路，RDARS的每个单元均可动态编程，通过光纤与基站（BS）连接，并作为BS的远端分布式天线以连接模式运行，用于接收或发送信号。此外，RDARS通过默认将单元配置为无源模式以执行反射操作，从而继承了完全无源RIS的低成本和低能耗优势。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，并推导了具有深刻见解的闭式表达式。理论分析和仿真结果证明，RDARS实现了比DAS和RIS更高的可达速率。本文构建了一个包含256个单元的RDARS原型进行实际实验，结果表明，与DAS和RIS辅助系统相比，RDARS辅助系统分别可额外提升21%和170%的吞吐量。