Intelligent reflecting surfaces (IRSs) have the potential to transform wireless communication channels into smart reconfigurable propagation environments. To realize this new paradigm, the passive IRSs have to be large, especially for communication in far-field scenarios, so that they can compensate for the large end-to-end path-loss, which is caused by the multiplication of the individual path-losses of the transmitter-to-IRS and IRS-to-receiver channels. However, optimizing a large number of sub-wavelength IRS elements imposes a significant challenge for online transmission. To address this issue, in this paper, we develop a physics-based model and a scalable optimization framework for large IRSs. The basic idea is to partition the IRS unit cells into several subsets, referred to as tiles, model the impact of each tile on the wireless channel, and then optimize each tile in two stages, namely an offline design stage and an online optimization stage. For physics-based modeling, we borrow concepts from the radar literature, model each tile as an anomalous reflector, and derive its impact on the wireless channel for a given phase shift by solving the corresponding integral equations for the electric and magnetic vector fields. In the offline design stage, the IRS unit cells of each tile are jointly designed for the support of different transmission modes, where each transmission mode effectively corresponds to a given configuration of the phase shifts that the unit cells of the tile apply to an impinging electromagnetic wave. In the online optimization stage, the best transmission mode of each tile is selected such that a desired quality-of-service (QoS) criterion is maximized. We show that the proposed modeling and optimization framework can be used to efficiently optimize large IRSs comprising thousands of unit cells.

中文翻译：

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基于物理的大型智能反射面建模与可扩展优化

智能反射面 (IRS) 具有将无线通信信道转变为智能可重构传播环境的潜力。为了实现这种新范式，无源 IRS 必须很大，特别是对于远场场景中的通信，以便它们可以补偿由单个路径倍增引起的较大的端到端路径损耗- 发射机到 IRS 和 IRS 到接收机通道的损耗。然而，优化大量亚波长 IRS 元素对在线​​传输提出了重大挑战。为了解决这个问题，在本文中，我们为大型 IRS 开发了一个基于物理的模型和一个可扩展的优化框架。基本思想是将 IRS 单位单元划分为几个子集，称为瓦片，模拟每个瓦片对无线信道的影响，然后分两个阶段优化每个瓦片，即离线设计阶段和在线优化阶段。对于基于物理的建模，我们借鉴了雷达文献中的概念，将每个瓦片建模为一个异常反射器，并通过求解相应的电场和磁场矢量场积分方程，推导出给定相移对无线信道的影响。在离线设计阶段，每个瓦片的 IRS 单位单元被联合设计以支持不同的传输模式，其中每个传输模式有效地对应于瓦片的单位单元应用于撞击电磁的相移的给定配置。海浪。在在线优化阶段，选择每个瓦片的最佳传输模式，使得期望的服务质量 (QoS) 标准最大化。