In this letter, we optimize the channel estimator of the cascaded channel in an intelligent reflecting surface (IRS)-assisted millimeter wave (mmWave) multi-antenna system. In this system, the receiver is equipped with a hybrid architecture adopting quantized beamforming. Different from traditional multiple-input multiple-output (MIMO) systems, the design of channel estimation is challenging since the IRS is usually a passive array with limited signal processing capability. We derive the optimized channel estimator in a closed form by reformulating the problem of cascaded channel estimation in this system, leveraging the typical mean-squared error (MSE) criterion. Considering the presence of possible channel sparsity in mmWave channels, we generalize the proposed method by exploiting the channel sparsity for further performance enhancement and computational complexity reduction. Simulation results verify that the proposed estimator significantly outperforms the existing ones.

中文翻译：

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具有量化波束成形的 IRS 辅助毫米波多天线级联信道估计

在这封信中，我们优化了智能反射面 (IRS) 辅助毫米波 (mmWave) 多天线系统中级联信道的信道估计器。在该系统中，接收器配备了采用量化波束成形的混合架构。与传统的多输入多输出 (MIMO) 系统不同，信道估计的设计具有挑战性，因为 IRS 通常是一个信号处理能力有限的无源阵列。我们利用典型的均方误差 (MSE) 标准，通过重新阐述该系统中级联信道估计的问题，以封闭形式推导出优化的信道估计器。考虑到毫米波信道中可能存在的信道稀疏性，我们通过利用信道稀疏性来推广所提出的方法，以进一步提高性能和降低计算复杂度。仿真结果验证了所提出的估计器明显优于现有的估计器。