Reconfigurable Distributed Antennas and Reflecting Surface: A New Architecture for Wireless Communications

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 fully digital or hybrid 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 coverage and 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 &#x201C;Reconfigurable Distributed Antennas and Reflecting Surfaces (RDARS)&#x201D; 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 <italic>connected mode</italic> 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 <italic>reflection mode</italic>. As a result, RDARS encompasses both DAS and RIS as special cases, offering flexible control over the trade-off between <italic>distribution gain</italic> and <italic>reflection gain</italic> to enhance performance. To unveil the potential of such architecture, the ergodic achievable rate under the RDARS architecture is analyzed and closed-form expression with meaningful insights is derived. The theoretical analysis proves that the RDARS can achieve a higher achievable rate than both DAS and fully passive RIS with the passive beamforming gain provided by elements acting <italic>reflection mode</italic> while combating the &#x201C;multiplicative fading&#x201D; suffered by RISs through the <italic>connected mode</italic> performed at the RDARS. Simulation results also demonstrate the superiority of the RDARS architecture over DAS and passive RIS-aided systems and its flexible trade-off between performance and cost. To further validate the feasibility and effectiveness, an RDARS prototype with 256 elements is built for real experiments. Experimental results show that the RDARS-aided system with only one element operating in <italic>connected mode</italic> can achieve an additional 21% and 170% throughput improvement over DAS and RIS-aided systems, respectively.