In this paper, we study how to jointly design the phase shift of cascaded multi-IRSs and the precoding vector of the BS to improve the coverage in dense urban areas. We aim to maximize the signal-to-noise ratio (SNR) of the user equipment (UE) received signal by employing this method. However, it is a constrained non-convex optimization problem and is NP-hard. In order to solve this problem, we simplify it by utilizing the characteristic of the mmWave wireless system to decompose the optimization problem into multiple sub-optimization problems. By employing the asymptotic orthogonality of wireless channel in mmWave system to solve the sub-optimization problems, we finally yield a closed-form sub-optimal solution. The simulation results verify that our solution can effectively improve the coverage of deep dense urban areas.

翻译：在本文中,我们研究如何共同设计级联多IRS和BS预编码矢量的分阶段转换,以扩大密集城市地区的覆盖面。我们的目标是通过使用这种方法最大限度地扩大用户设备收到的信号的信号对噪音比率(SNR),然而,这是一个有限的非电流优化问题,而且是NP-硬的。为了解决这个问题,我们通过利用毫米Wave无线系统的特性将优化问题分解为多个次优化问题来简化它。我们利用毫米Wave系统中无线通道的无线通道的无线性或多位化来解决亚优化问题,我们终于产生了一个封闭式次优化解决方案。模拟结果证实我们的解决方案能够有效地改善密度较大的城市地区的覆盖面。