Dynamic metasurface antennas (DMAs), with their ability to manipulate electromagnetic waves using tunable metamaterial elements, provide a promising solution for beamforming in next-generation wireless communication systems. However, practical constraints, such as discrete phase shifts and the Lorentzian constraint, pose significant challenges for their optimization. This paper investigates the beamforming optimization problem in a downlink system where a base station (BS) equipped with a DMA operates under arbitrary discrete phase shift constraints. We propose two algorithms: the closest point projection (CPP) algorithm, which efficiently projects continuous-phase solutions onto discrete domains with lower complexity, and the optimalM-phase beamforming (OMPB) algorithm, which is proven to achieve the globally optimal solution for discrete phase configurations. We derive closed-form expressions for the quantization performance loss and average signal-to-noise ratio (SNR). Our analysis reveals that the quantization-induced performance losses for 1-bit, 2-bit, and 3-bit uniform phase configurations are 3.74 dB, 0.87 dB, and 0.22 dB, respectively. Extensive Monte-Carlo simulations validate the theoretical analysis and demonstrate that the proposed methods achieve notable performance gains over traditional relaxation and random algorithms.

Reconfigurable intelligent surface (RIS) is a promising technology that has the potential to change the way we interact with the wireless propagating environment. In this paper, we propose a practical two-stage spatial-oversampling codebook algorithm for the beamforming of RIS, which is based on the spatial structure of the wireless channel. This algorithm has significantly lower complexity compared to the two-dimensional full-space searching-based codebook, yet with only negligible performance loss in the experiment. Then, a series of experiments are conducted with the fabricated RIS systems, covering office, corridor, and outdoor environments, to verify the effectiveness of RIS in both laboratory and current fifth generation (5G) commercial networks. In the office and corridor scenarios, the 5.8 GHz RIS provided a power gain of $\mathbf{1 0 - 2 0 ~ d B}$ at the receiver. In commercial 5G networks, the 2.6 GHz RIS improved indoor signal strength by 4-7 dB.

Most research works on reconfigurable intelligent surfaces (RIS) rely on idealized models of the reflection coefficients, i.e., uniform reflection amplitude for any phase and sufficient phase shifting capability. In practice however, such models are oversimplified. This paper introduces a realistic reflection coefficient model for RIS based on measurements. The reflection coefficients are modeled as discrete complex values that have non-uniform amplitudes and suffer from insufficient phase shift capability. We then propose a group-based query algorithm that takes the imperfect coefficients into consideration while calculating the reflection coefficients. We analyze the performance of the proposed algorithm, and derive the closed-form expressions to characterize the received power of an RIS-aided wireless communication system. The performance gains of the proposed algorithm are confirmed in simulations. Furthermore, we validate the proposed theoretical results by experiments with our fabricated RIS prototype systems. The simulation and measurement results match well with the theoretical analysis.

The prospects of using a Reconfigurable Intelligent Surface (RIS) to aid wireless communication systems have recently received much attention from academia and industry. Most papers make theoretical studies based on elementary models, while the prototyping of RIS-aided wireless communication and real-world field trials are scarce. In this paper, we describe a new RIS prototype consisting of 1100 controllable elements working at 5.8 GHz band. We propose an efficient algorithm for configuring the RIS over the air by exploiting the geometrical array properties and a practical receiver-RIS feedback link. In our indoor test, where the transmitter and receiver are separated by a 30 cm thick concrete wall, our RIS prototype provides a 26 dB power gain compared to the baseline case where the RIS is replaced by a copper plate. A 27 dB power gain was observed in the short-distance outdoor measurement. We also carried out long-distance measurements and successfully transmitted a 32 Mbps data stream over 500 m. A 1080p video was live-streamed and it only played smoothly when the RIS was utilized. The power consumption of the RIS is around 1 W. Our paper is vivid proof that the RIS is a very promising technology for future wireless communications.