RIS-Aided Wireless Communications: Prototyping, Adaptive Beamforming, and Indoor/Outdoor Field Trials (2103.00534v2)

Abstract: 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.

• The paper demonstrates that a RIS prototype with 1100 elements operating at 5.8 GHz delivers up to 27 dB power gain in both indoor NLoS and outdoor scenarios.
• The study employs a novel feedback-based adaptive beamforming algorithm that configures the RIS in real-time without altering existing communication protocols.
• Field trials validate the RIS's effectiveness by relaying high-speed data (32 Mbps) and streaming 1080p video over distances up to 500m with low energy consumption.

Overview of RIS-Aided Wireless Communications Prototyping and Field Trials

The paper presents a comprehensive paper on the practical implementation and performance evaluation of Reconfigurable Intelligent Surface (RIS)-aided wireless communication systems. While much attention has been garnered by RIS technologies in theoretical contexts, this research emphasizes the pragmatic aspects by advancing a prototype and assessing its applicability through extensive indoor and outdoor trials. The paper strives to bridge the gap between theoretical expectations and real-world operational performance.

Technical Contributions and Findings

The implemented RIS prototype consists of 1100 controllable elements operating at a frequency of 5.8 GHz. The authors developed an efficient algorithm that exploits the intrinsic properties of the geometric array for configuring the RIS directly over the air. Significant findings from the prototyping and experiments are:

1. Indoor Tests with Non-Line-of-Sight (NLoS) Scenarios: The paper achieved a remarkable 26 dB power gain using the RIS compared to a baseline where a copper plate was used in similar conditions. The transmission occurred around significant concrete obstruction, emphasizing the RIS's role in enhancing signal strength in challenging propagation environments.
2. Short-Distance Outdoor Measurements: In settings where the transmission distance was reduced, a consistent power gain of 27 dB was recorded. This reinforces the RIS's potential to mitigate propagation losses effectively.
3. Long-Distance Outdoor Trials: The research conducted experiments over 500m, successfully relaying a 32 Mbps data stream, which entailed smooth streaming of 1080p video exclusively when the RIS was active. While the gain was relatively lower at 14 dB, it illustrates the RIS's efficacy in enlarging the coverage area.

The power consumption of the RIS maintained at approximately 1 W, showcasing its energy efficiency potential.

Algorithmic Development and Implementations

A novel feedback-based adaptive reflection coefficient optimization algorithm was proposed. This innovation allows for real-time beamforming without needing to adapt existing communication protocols, making it an adaptable addition to current communication infrastructures. Notably, the algorithm optimizes RIS configuration to raise the amplitude-level at the receiver side, underscoring a pragmatic approach aligned to the existing wireless standards.

Challenges and Future Directions

The research highlighted practical considerations, such as the incident-angle-dependent behavior of the RIS, which deviates from canonical models predominantly used in the academia. The non-ideal features, including the phase variations caused by different incident angles, necessitate refined models to better represent real-world scenarios. Acknowledging these non-linearities is critical to developing more robust, optimized designs in future implementations.

Further research could delve into expanding the resolution of RIS configurations beyond the binary states employed here (1-bit phase resolution). Enhanced resolution could potentially mitigate performance degradation in more complex environments with multifaceted propagation characteristics. Additionally, integrating machine learning techniques might further optimize the RIS configuration dynamics in real-time, adapting to fluctuating channel conditions.

Implications

The implications of this paper are significant for the future of wireless communications, particularly as the demand for higher capacity and more flexible network topologies expands with the proliferation of 5G and beyond. RIS technology offers a path towards more energy-efficient, high-performance networks by empowering adaptive environmental control on signal propagation.

In summary, the research substantiates RIS technology as a promising augmentative solution for future wireless communication systems. Its low power consumption, adaptability, and proven gains in both controlled and harsh environments mark it as a pivotal technology in the ongoing evolution of wireless infrastructure. As theoretical investigations converge with practical applications, RIS technologies are poised to play a crucial role in the next-generation communication paradigms.