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Reconfigurable Intelligent Surface-Based Wireless Communication: Antenna Design, Prototyping and Experimental Results
Linglong Dai, Bichai Wang, Min Wang, Xue Yang, Jingbo Tan, Shuangkaisheng Bi, Shenheng Xu, Fan Yang, Zhi Chen, Marco Di Renzo, Lajos Hanzo
TL;DR
Conventional phased arrays make massive-MIMO scaling costly and power-intensive. The paper develops a 256-element 2-bit RIS and a modular wireless prototype, demonstrating phase control, beam scanning, and measured communication-system gains. The results support the feasibility and efficiency of RIS-based wireless communications within the tested settings.
Problem
Conventional phased arrays require numerous phase shifters and complex feeding networks, creating high power consumption and hardware cost for practical massive-MIMO arrays.
Method
The paper constructs 2-bit RIS elements combining phase shifting and radiation, then integrates a 256-element RIS with hosts and USRPs into a wireless communication prototype.
Results
18.0 dBi measured gain at a 60° scanning angle corresponded to only 3.7 dB scanning gain reduction, while the prototype reached 51.7 dBm EIRP at 30 dBm transmitted power.
Takeaways & Limitations
The experiments demonstrate the feasibility and efficiency of a 256-element 2-bit RIS for energy-efficient wireless communications and flexible wide-angle beam scanning.
Abstract
from arXiv · showhide
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.
I. INTRODUCTION
Massive MIMO can greatly improve spectral efficiency, but conventional phased arrays require many power-hungry phase shifters and complex feeding networks. This paper proposes a 256-element, 2-bit RIS and develops a modular wireless communication prototype using it.
- I. INTRODUCTION: Massive MIMO improves spectral efficiency through large antenna arrays, but conventional phased arrays require hundreds of high-resolution phase shifters and complex feeding networks.These requirements limit practical antenna-array scale through high power consumption and hardware cost.
- I. INTRODUCTION: RISs offer an alternative based on many nearly passive elements that electronically control incident-wave phase with ultra-low power consumption.Their spatial feeding mechanism is presented as avoiding excessive power loss from bulky feeding networks.
- I. INTRODUCTION: 1-bit RIS elements provide only two phase states and can reduce antenna gain by more than 3 dB because of phase errors.The supplied passage identifies low-resolution phase control as the source of this reduction.
- I. INTRODUCTION: The paper fabricates and measures 16×16 RISs with 2-bit elements at 2.3 GHz and 28.5 GHz, and develops the first wireless communication prototype using 256 such elements.The RIS is used for beamforming during both transmission and reception, unlike the cited metasurface prototype used for transmission-only signal modulation.
- I. INTRODUCTION: The prototype combines hosts for parameter setting and data exchange, USRPs for baseband and RF processing, and the RIS for signal transmission and reception.The transmitter USRP performs source coding, channel coding, and OFDM modulation before RIS transmission; the receiver USRP processes the received signal.
II. THE RIS WITH 2-BIT ELEMENTS
The proposed RIS combines radiation and electronic 2-bit phase shifting in a low-cost surface element using PIN-controlled RF current paths. A fabricated 16 × 16 array demonstrates stable simulated phase states, low insertion loss, and steerable high-gain beams.
- Element structure: The novel element structure combines an upper patch, slot-loaded plane, and ground plane to receive, control, and reradiate electromagnetic energy.The slot-loaded plane controls the phase state, while the ground plane suppresses back radiation.
- Element structure: Five PIN diodes are integrated into four symmetric slot sets and independently controlled through two bias lines.The diode groups use +0.9 V and −0.9 V forward and reverse DC voltages.
- Phase control: The diode states control RF current paths and slot resonant lengths, producing four phase states with an approximate 90° increment.This realizes 2-bit phase resolution without conventional phase shifters.
- Polarization: The symmetric element structure supports the same performance for x- and y-polarized incident waves, suiting dual-linearly and dual-circularly polarized systems.Incident and reradiated fields are orthogonally polarized because the current directions change.
- Simulated performance: The four simulated phase states remain stable from 2 GHz to 2.6 GHz, while insertion magnitude loss stays below 1.2 dB.The element configurations exhibit similar magnitude responses in paired states and approximately 180° phase differences due to current reversal.
- Array implementation: A fabricated 16 × 16 RIS array dynamically converts the feed’s spherical wavefront into a planar wavefront and switches beams across a two-dimensional ±60° range.The surface measures 800 mm × 800 mm, with the primary feed 720 mm away.
III. RIS-BASED WIRELESS COMMUNICATION PROTOTYPE
The prototype combines a 256-element 2-bit RIS with modular hardware and flexible software to implement end-to-end wireless transmission and reception. Its processing follows an LTE-based FDD signal chain with configurable transmission parameters.
- Hardware architecture: The prototype integrates a transmitter host, USRPs, a 256-element 2-bit RIS, a receiver antenna, and a receiver host.The hardware is divided between base-station and user sides.
- Software control: Flexible software controls parameters including carrier frequency, transmit power, modulation, and coding modes.The graphical interface at the transmitter host configures these operating settings.
- Implementation: The baseband processing follows the LTE standard with frequency division duplex and is implemented on a high-speed FPGA processor.Graphical programming supports the FPGA implementation.
- Transmitter processing: The transmitter performs source coding, channel coding, interleaving, and OFDM processing before RF transmission through the RIS.OFDM is used for wideband transmission over dispersive channels.
- Receiver processing: The receiver reverses the transmission process, using synchronization signals and pilots for synchronization and channel estimation before signal detection.Recovered signals and communication parameters are displayed at the receiver host.
IV. EXPERIMENTAL RESULTS
Measurements characterize the RIS beam patterns, gain, scanning performance, and wireless prototype operation at 2.3 GHz and 28.5 GHz. The prototype also demonstrates over-the-air transmission of high-definition VR video.
- 2.3 GHz antenna measurements: The 2.3 GHz broadside beam has measured half-power beamwidths of 9.1° and 8.8° in the two principal planes.Measured sidelobe levels are −16.7 dB and −16.4 dB, respectively.
- 2.3 GHz antenna measurements: 21.9 dBi is the maximum measured gain at 2.4 GHz, with a 350 MHz 1-dB gain bandwidth.The bandwidth corresponds to 15.2% at the 2.3 GHz design frequency.
- Beam scanning: The RIS scans beams from 0° to 60°, while increasing scan angle reduces measured gain and broadens the main beam.The measured patterns are normalized to the broadside-beam gain.
- Beam scanning: 18.0 dBi is the measured gain at a 60° scanning angle, corresponding to a scanning gain reduction of only 3.7 dB.These measurements verify wide-angle beam scanning with the 2-bit RIS.
- Wireless communication prototype: The 2.3 GHz OTA prototype transmits high-definition VR video over a 20-meter indoor link, with clearly separated received 64QAM symbols.The system uses 1200 OFDM subcarriers and supports QPSK, 16QAM, and 64QAM.
- Wireless communication prototype: 51.7 dBm is the prototype EIRP at 30 dBm transmitted power, providing a 2 dB gain over 1-bit RIS-based wireless communication systems.A separate 28.5 GHz prototype achieves a measured gain of 19.1 dBi.
V. CONCLUSIONS
The paper concludes that a 256-element 2-bit RIS can support energy-efficient wireless communication with high measured antenna gain and reduced power consumption.
- Conclusions: The proposed RIS has 256 2-bit elements and significantly reduces the power consumption and hardware cost of conventional phased arrays.The paper reports experimental evaluation of the fabricated and measured surface.
- Conclusions: 21.7 dBi is obtained at 2.3 GHz, while 19.1 dBi is achieved at 28.5 GHz.These are the reported antenna gains for the two operating frequencies.
- Conclusions: OTA tests show significantly reduced power consumption without degrading EIRP compared with existing wireless communication systems.The conclusion attributes this result to the proposed RIS-based wireless communication system.