Intelligent reflecting surfaces (IRSs) have received considerable attention
from the wireless communications research community recently. In particular, as
low-cost passive devices, IRSs enable the control of the wireless propagation
environment, which is not possible in conventional wireless networks. To take
full advantage of such IRS-assisted communication systems, both the beamformer
at the access point (AP) and the phase shifts at the IRS need to be optimally
designed. However, thus far, the optimal design is not well understood. In this
paper, a point-to-point IRS-assisted multiple-input single-output (MISO)
communication system is investigated. The beamformer at the AP and the IRS
phase shifts are jointly optimized to maximize the spectral efficiency. Two
efficient algorithms exploiting fixed point iteration and manifold optimization
techniques, respectively, are developed for solving the resulting non-convex
optimization problem. The proposed algorithms not only achieve a higher
spectral efficiency but also lead to a lower computational complexity than the
state-of-the-art approach. Simulation results reveal that deploying large-scale
IRSs in wireless systems is more efficient than increasing the antenna array
size at the AP for enhancing both the spectral and the energy efficiency.

本文研究了点对点 IRS 辅助多输入单输出通信系统中 AP 波束赋形器以及 IRS 相移的联合优化，提出了固定点迭代和流形优化技术两种有效算法，其不仅能够提高频谱效率，而且计算复杂度更低。仿真结果表明，在无线系统中部署大规模的 IRS 较增加 AP 天线阵列的效率更高，可以提高频谱和能量效率。