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

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 intrinsicnegative (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.

Smart Radio Environments Empowered by Reconfigurable Intelligent Surfaces: How It Works, State of Research, and The Road Ahead

“…In [286], the authors report a new type of high-gain yet low-cost RIS made of 256 elements. The proposed RIS combines the functions of phase shift and EM radiation on an electromagnetic surface where PIN diodes are used to realize two-bit phase shifts for beamforming.…”

Reconfigurable Intelligent Surface Aided NOMA Networks

“…is a diagonal matrix, which accounts for the effective phase shift applied by all intelligent surfaces, β n ∈ (0, 1] represents the amplitude reflection coefficient of RISs, while φ n = exp(jθ n ), j = √ −1, ∀n = 1, 2 • • • , N , and θ n ∈ [0, 2π) denotes the phase shift introduced by the n-th intelligent surface. Based on the insights from [38], the amplitude coefficient of each RIS elements can be different, but in order to obtain tractable analytical results, we set β 1 , . .…”

“…SE of the proposed RIS-aided NOMA network versus the SNR and the number of RISs. The results of POD and FOD are calculated from(38) and[27]. The fading parameters are set to m 1 = m W = m v = 3.…”

Intelligent Reflecting Surfaces With Spatial Modulation: An Electromagnetic Perspective

“…(3) Analyzing (2) and 3, it is evident that, a constructive interference can be achieved in a given (θ, φ) direction by maximizing the exponential term (and hence the AF) for the steering angle of interest. To achieve this, the phase advance introduced by the unit cells of the reflecting surface must be chosen as the complex conjugate of (3) as follows:…”

“…For these reasons, it comes as no surprise that the related literature has been fast expanding with numerous papers appearing over the last two years. In this context, it is worth mentioning the stream of publications on channel estimation for IRS [7], [8], precoding design [9], [10] and physical prototyping [2], [11].…”