[论文解读] Reconfigurable Intelligent Surface-Based Wireless Communication: Antenna Design, Prototyping and Experimental Results

Linglong Dai, Bichai Wang+9 more|arXiv (Cornell University)|Dec 8, 2019

Advanced Wireless Communication Technologies参考文献 21被引用 8

一句话总结

本论文展示了具有256个两比特移相元件的可重构智能表面（RIS）的设计、原型制作及实验验证，实现了高效能、高增益的无线通信。该RIS通过PIN二极管实现辐射与相位控制一体化，2.3 GHz频段下实现21.7 dBi增益，28.5 GHz频段下实现19.1 dBi增益，过空气（OTA）测试证实可实现实时高清VR视频传输，并相较1比特RIS系统实现2 dB EIRP增益。

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.

研究动机与目标

• 解决未来无线网络中传统大规模MIMO相控阵带来的高功耗与高硬件成本问题。
• 开发一种基于可重构智能表面（RIS）的低成本、低功耗替代方案，实现多比特相位控制。
• 设计并原型化一个256单元、具备两比特移相功能的RIS，以实现灵活波束成形与高方向性。
• 通过在Sub-6 GHz与毫米波频段进行过空气（OTA）实验，验证基于RIS的无线通信的可行性与性能。
• 展示利用RIS原型实现实时高速率应用，如高清VR视频流传输。

提出的方法

• RIS采用256单元阵列，每个单元利用PIN二极管实现两比特移相（0°、90°、180°、270°），无需主动射频链路即可实现波束成形。
• RIS结构将辐射单元与相位控制功能集成于单一电磁表面上，消除了复杂的馈电网络，降低了功耗。
• 波束成形控制板可动态调节256个单元的相位状态，实现主波束在宽角度范围（最高±60°）内的扫描。
• 原型采用USRPs进行基带与射频信号处理，主机负责参数设置与数据交换，实现全软件定义操作。
• 系统工作于2.3 GHz与28.5 GHz频段，采用OFDM调制、QAM与Turbo编码，以实现高谱效率与强健性。
• 在室内环境中开展过空气（OTA）测试，链路距离20米，以高分辨率立体VR视频作为数据源。

实验结果

研究问题

• RQ1 具备两比特移相器的256单元RIS是否能实现足够的方向性与波束成形增益，以支持高速率无线通信？
• RQ2 与1比特RIS相比，两比特RIS在有效全向辐射功率（EIRP）与频谱效率方面表现如何？
• RQ3 能否通过模块化硬件与灵活软件实现一个功能完整的RIS无线通信原型，以支持实时数据传输？
• RQ4 RIS在不同扫描角度下的波束扫描能力与增益退化情况如何？
• RQ5 RIS原型能否支持实时高速率应用，如高清VR视频流传输？

主要发现

• 在2.3 GHz频段，RIS实测增益达21.7 dBi，峰值增益21.9 dBi（2.4 GHz），1-dB带宽为350 MHz（相对带宽15.2%）。
• 在28.5 GHz频段，RIS实测增益达19.1 dBi，证明其在毫米波频段的可行性。
• RIS实现从 broadside 到60°的宽角波束扫描，仅造成3.7 dB增益下降，证实其具备灵活波束成形能力。
• 过空气测试证实，采用64-QAM调制可实现高清3920×1440 VR视频的实时传输，星座图分离清晰，数据速率稳定。
• 原型EIRP达51.7 dBm（发射功率30 dBm），相较现有1比特RIS系统提升2 dB。
• 与传统相控阵相比，系统展现出显著的功耗降低，验证了RIS通信的高能效特性。