Intelligent reflecting surface (IRS) is envisioned as a revolutionary technology for future wireless communication systems since it can intelligently change radio environment and integrate it into wireless communication optimization. However, most existing works adopted an ideal IRS reflection model, which is impractical and can cause significant performance degradation in realistic wideband systems. To address this issue, we first study the dual phase- and amplitude-squint effect of reflected signals and present a simplified practical IRS reflection model for wideband signals. Then, an IRS enhanced wideband multiuser multi-input single-output orthogonal frequency division multiplexing (MU-MISO-OFDM) system is investigated. We aim to jointly design the transmit beamformer and IRS reflection for the case of using both continuous and discrete phase shifters to maximize the average sum-rate over all subcarriers. By exploiting the relationship between sum-rate maximization and mean square error (MSE) minimization, the original problem is equivalently transformed into a multi-block/variable problem, which can be efficiently solved by the block coordinate descent (BCD) method. Complexity and convergence for both cases are analyzed or illustrated. Simulation results demonstrate that the proposed algorithm can offer significant average sum-rate enhancement compared to that achieved using the ideal IRS reflection model, which confirms the importance of the use of the practical model for the design of wideband systems.

中文翻译：

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智能反射面增强型宽带 MIMO-OFDM 通信：从实用模型到反射优化

智能反射面 (IRS) 被设想为未来无线通信系统的革命性技术，因为它可以智能地改变无线电环境并将其集成到无线通信优化中。然而，大多数现有工作采用了理想的 IRS 反射模型，这是不切实际的，并且会导致现实宽带系统的性能显着下降。为了解决这个问题，我们首先研究反射信号的双相位和幅度斜视效应，并提出了宽带信号的简化实用 IRS 反射模型。然后，研究了IRS增强型宽带多用户多输入单输出正交频分复用（MU-MISO-OFDM）系统。我们的目标是在使用连续和离散移相器的情况下联合设计发射波束形成器和 IRS 反射，以最大化所有子载波的平均总和速率。通过利用和速率最大化和均方误差（MSE）最小化之间的关系，将原始问题等效地转化为多块/变量问题，可以通过块坐标下降（BCD）方法有效解决。分析或说明了这两种情况的复杂性和收敛性。