Modeling, Optimization, and Hardware Design of Intelligent Reflecting Surface Assisted Wireless Communication Systems

在过去的几十年里，已经开发了各种技术来提高无线通信系统的频谱和功率效率。这些技术包括(大规模)多输入多输出(MIMO)、全双工通信和非正交多址。尽管这些计划和其他类似的方法具有显著的优势，但它们也有局限性。特别是，它们的有效性关键取决于无线通道。如果信道的散射体很少或/并且发射机和接收机之间没有视距(LOS)，则性能可能会严重下降。然而，到目前为止，几乎所有改善无线通信系统性能的尝试都集中在发射机和/或接收机上。无线频道本身一直被视为“上天赐予的”。为了克服这一限制，最近，人们提出了在无线系统中引入大反射面的想法，这种反射面的电磁(EM)特性可以通过外部控制。这些智能反射面(IRS)可以部署在室外建筑物的立面上，也可以部署在室内的墙上，以帮助发射器和接收器之间的通信。从通信系统设计的角度来看，IR构成了一种完全的范式转变，因为它们第一次允许操纵无线信道的属性。然而，IRS辅助无线通信系统的研究还处于起步阶段，为了充分评估和挖掘其巨大的潜力，需要一种涵盖IRS辅助无线通信系统的建模、优化和实现的整体设计方法。为了实现这一目标，我们组建了一支在信号处理和通信(Schober，数字通信研究所)、EM建模和天线设计(Vossiek，微波与光子学研究所)以及收发器设计和实施(Weigel，电子工程研究所)方面拥有丰富专业知识的研究团队。该项目的具体目标包括：1)根据电磁波传播及其与IRS相互作用的物理规律，建立IRS辅助无线系统的通用通信理论模型。2)设计和优化IRS辅助无线系统，包括波束形成、资源分配和信道估计。3)设计和实现完全模块化和灵活的IRS，具有耦合和孔径效率优化的单元单元和能够进行大规模测量的阵列设计。4)基于实验的验证和改进所提出的理论模型以及单元单元、阵列、该项目的预期成果包括经过实验验证的IRS辅助无线通信的分析模型和设计框架，以及一个完全运行的IRS试验台。

Over the past decades, various techniques have been developed to improve the spectral and power efficiency of wireless communication systems. These techniques include (massive) multiple-input multiple-output (MIMO), full duplex communication, and non-orthogonal multiple access. Despite their significant advantages, these schemes and other similar approaches also have limitations. In particular, their effectiveness crucially depends on the wireless channel. If the channel has few scatterers or/and there is no line-of-sight (LoS) between transmitter and receiver, performance may severely degrade. However, so far, practically all attempts to improve the performance of wireless communication systems have focused on the transmitter and/or the receiver. The wireless channel itself has always been viewed as "God-given". To overcome this limitation, very recently, the idea of introducing large reflecting surfaces, whose electromagnetic (EM) properties can be externally controlled, into wireless systems was presented. These intelligent reflecting surfaces (IRSs) may be deployed outdoors on the facades of buildings or indoors on walls to assist the communication between the transmitters and receivers. From a communication system design point of view, IRS constitute a complete paradigm shift as they allow, for the first time, the manipulation of the properties of the wireless channel. However, the research on IRS-assisted wireless communication systems is still in its infancy.To fully evaluate and exploit their tremendous potential, a holistic design approach covering the modeling, optimization, and implementation of IRS-assisted wireless communication systems is needed. To accomplish this, we have assembled a team of researchers with significant expertise in signal processing and communications (Schober, Institute for Digital Communications), EM modelling and antenna design (Vossiek, Institute of Microwaves and Photonics), and transceiver design and implementation (Weigel, Institute for Electronics Engineering). The specific objectives of the proposed project include:1) Development of a general communication-theoretical model for IRS-assisted wireless systems based on the laws of physics governing the propagation of EM waves and their interaction with the IRS.2) Design and optimization of IRS-assisted wireless systems including beamforming, resource allocation, and channel estimation.3) Design and implementation of a fully modularized and flexible IRS with coupling and aperture efficiency optimized unit cells and an array design enabling large-scale measurements.4) Experiment based verification and refinement of the proposed theoretical models as well as the unit cell, array, and signal designs.The expected outcomes of this project include experimentally verified analytical model and design frameworks for IRS-assisted wireless communications as well as a fully operational IRS testbed.