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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. In existing massive MIMO systems, however, conventional phased arrays are used for beamforming. This method results in excessive power consumption and high hardware costs. 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 develop a new type of high-gain yet low-cost RIS that bears 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. This radical design forms the basis for the world's first wireless communication prototype using RIS having 256 two-bit elements. The prototype consists of modular hardware and flexible software that encompass the following: 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 wireless communications. We show that, at 2.3 GHz, the proposed RIS can achieve a 21.7 dBi antenna gain. At the millimeter wave (mmWave) frequency, that is, 28.5 GHz, it attains a 19.1 dBi antenna gain. Furthermore, it has been shown that the RIS-based wireless communication prototype developed is capable of significantly reducing the power consumption.
Highlights
Massive multiple-input multiple-output (MIMO) schemes constitute promising techniques for future wirelessThe associate editor coordinating the review of this manuscript and approving it for publication was Kezhi Wang.communications
Once the signals from the transmitter host have been received, the universal software radio peripherals (USRPs) at the transmitter carries out the signal processing, which aims to transform the signals into a form suitable for transmission in wireless channels. (Later we introduce the detailed signal processing flow.) After that, the processed signals are forwarded to the reconfigurable intelligent surface (RIS) having 256 2-bit elements
Our prototype significantly reduced the power consumption and hardware cost of the conventional phased arrays
Summary
Massive multiple-input multiple-output (MIMO) schemes constitute promising techniques for future wirelessThe associate editor coordinating the review of this manuscript and approving it for publication was Kezhi Wang.communications. Massive multiple-input multiple-output (MIMO) schemes constitute promising techniques for future wireless. By relying on a large antenna array, massive MIMO schemes provide a substantial power gain and improve the spectral efficiency by orders of magnitude [1], [2]. L. Dai et al.: RIS-Based Wireless Communications and this requires hundreds of high-resolution phase shifters and complex feeding networks [3], [4]. The high power consumption and hardware cost of these phase shifters and complex feeding networks limit the antenna array scale in practical massive MIMO systems. The potential advantages of massive MIMO schemes cannot be fully realized
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