In the intelligent reflecting surface (IRS)-enhanced wireless communication system, channel state information (CSI) is of paramount importance for achieving the passive beamforming gain of IRS, which, however, is a practically challenging task due to its massive number of passive elements without transmitting/receiving capabilities. In this letter, we propose a practical transmission protocol to execute channel estimation and reflection optimization successively for an IRS-enhanced orthogonal frequency division multiplexing (OFDM) system. Under the unit-modulus constraint, a novel reflection pattern at the IRS is designed to aid the channel estimation at the access point (AP) based on the received pilot signals from the user, for which the channel estimation error is derived in closed-form. With the estimated CSI, the reflection coefficients are then optimized by a low-complexity algorithm based on the resolved strongest signal path in the time domain. Simulation results corroborate the effectiveness of the proposed channel estimation and reflection optimization methods.

中文翻译：

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智能反射表面增强型 OFDM：信道估计和反射优化

在智能反射面 (IRS) 增强型无线通信系统中，信道状态信息 (CSI) 对于实现 IRS 的无源波束成形增益至关重要，然而，由于其大量的无源元件，这是一项具有实际挑战性的任务没有发送/接收功能。在这封信中，我们提出了一种实用的传输协议，用于连续执行 IRS 增强正交频分复用 (OFDM) 系统的信道估计和反射优化。在单位模数约束下，IRS 处的新型反射模式被设计为基于从用户接收到的导频信号来辅助接入点 (AP) 处的信道估计，其信道估计误差以封闭形式导出. 使用估计的 CSI，然后基于解析出的时域最强信号路径，通过低复杂度算法优化反射系数。仿真结果证实了所提出的信道估计和反射优化方法的有效性。