Reconfigurable Intelligent Surface-Based Wireless Communication: Antenna Design, Prototyping and Experimental Results (1912.03620v1)

Abstract: One of the key enablers of future wireless communications is constituted by massive multiple-input multiple-output (MIMO) systems, which can improve the spectral efficiency by orders of magnitude. However, in existing massive MIMO systems, conventional phased arrays are used for beamforming, which result in excessive power consumption and hardware cost. Recently, reconfigurable intelligent surface (RIS) has been considered as one of the revolutionary technologies to enable energy-efficient and smart wireless communications, which is a two-dimensional structure with a large number of passive elements. In this paper, we propose and develop a new type of high-gain yet low-cost RIS having 256 elements. The proposed RIS combines the functions of phase shift and radiation together on an electromagnetic surface, where positive intrinsic-negative (PIN) diodes are used to realize 2-bit phase shifting for beamforming. Based on this radical design, the world's first wireless communication prototype using RIS having 256 2-bit elements is designed and developed. Specifically, the prototype conceived consists of modular hardware and flexible software, including the hosts for parameter setting and data exchange, the universal software radio peripherals (USRPs) for baseband and radio frequency (RF) signal processing, as well as the RIS for signal transmission and reception. Our performance evaluation confirms the feasibility and efficiency of RISs in future wireless communications. More particularly, it is shown that a 21.7 dBi antenna gain can be obtained by the proposed RIS at 2.3 GHz, while at the millimeter wave (mmWave) frequency, i.e., 28.5 GHz, a 19.1 dBi antenna gain can be achieved. Furthermore, the over-the-air (OTA) test results show that the RIS-based wireless communication prototype developed is capable of significantly reducing the power consumption.

• The paper introduces a 256-element RIS with integrated 2-bit phase shifting that delivers gains of 21.7 dBi at 2.3 GHz and 19.1 dBi at 28.5 GHz.
• It employs a novel antenna design merging phase shift and radiation functions to address limitations of traditional massive MIMO systems.
• The experimental prototype validates RIS technology’s potential by achieving high performance with lower power consumption and reduced hardware complexity.

Reconfigurable Intelligent Surface-Based Wireless Communication: Antenna Design, Prototyping and Experimental Results

The spotlight of the paper "Reconfigurable Intelligent Surface-Based Wireless Communication: Antenna Design, Prototyping and Experimental Results" is placed on the transformative role of Reconfigurable Intelligent Surfaces (RIS) in the landscape of wireless communications, showcasing a notable development in RIS comprising 256 elements. The authors propose an innovative approach to resolving the limitations associated with conventional massive multiple-input multiple-output (MIMO) systems. The RIS introduced in this paper offers a promising solution to overcoming excessive power consumption and high hardware costs typically seen with traditional phased arrays.

Overview and Context

Massive MIMO systems have been lauded for their potential to significantly boost spectral efficiency. However, the conventional phased arrays employed within these systems necessitate numerous high-resolution phase shifters and detailed feeding networks to accomplish beamforming. The accompanying increased power consumption and financial costs pose challenges to their scalability and implementation in practical scenarios.

RIS technology, structured from a multitude of passive elements, stands apart as a low-energy alternative. This approach circumvents the need for expensive and complex phase shifters by adopting positive intrinsic-negative (PIN) diodes for 2-bit phase shifting. The paper discusses the design and development of one of the first RIS-based wireless communication prototypes with 256 2-bit elements, demonstrating its functionality as both a transmitter and receiver component in a wireless communication system.

Technical Contributions

The paper's technical contribution is the innovative design of a two-bit RIS that intricately merges phase shift and radiation functions on an electromagnetic surface. This RIS, developed with positive intrinsic-negative (PIN) diodes, achieved a 21.7 dBi antenna gain at the lower frequency of 2.3 GHz and a 19.1 dBi gain at the higher millimeter-wave frequency of 28.5 GHz.

• Antenna Design and Characterisation: The proposed RIS consists of a detailed layout of modular hardware and customizable software components. The antenna structure involves specific design choices such as integrating a large number of nearly passive elements that control electromagnetic wave phases through electronic means.
• Prototype Development: The development of the world's first wireless communication prototype leveraging 256 2-bit elements is notable. Utilizing tools like universal software radio peripherals (USRPs) for baseband and RF signal processing this prototype confirms the practical viability and operational efficiency of RIS in reducing hardware costs while maintaining high performance.
• Performance Metrics: The paper's experimental evaluations reveal substantial power gain compared to the traditional phased array setups, achieving equivalent or superior performance in terms of effective isotropic radiated power (EIRP), while significantly reducing power consumption.

Practical and Theoretical Implications

The practical implications of adopting RIS technology are profound, offering a path toward more sustainable and economically feasible wireless networks. With a decrease in required power and simplification of the hardware components, RIS can facilitate broader deployment of high-efficiency communication systems across diverse terrain, air-to-ground, air-to-air data transmission, and satellite communications.

Theoretically, the paper advances the understanding of RIS technology and provides a template for future designs that can balance complexity, cost, and performance. It leads the way toward creating more versatile and adaptive wireless environments that could significantly reshape how wireless systems are conceptualized and built.

Future Developments

Looking ahead, the evolution of RIS technology may involve research focus on further reducing phase quantization errors and enhancing the efficiency of multi-bit element RIS. There is potential for expanding RIS applications into ultra-reliable low-latency communication (URLLC) and massive machine-type communications (mMTC), crucial for the forthcoming generations of wireless technology.

In synthesis, this paper offers a detailed exploration into RIS technology, providing a strong foundation for future research and development also setting a benchmark for wireless communication innovation by exhibiting feasible solutions for existing limitations with massive MIMO systems.