Conventional beamforming methods for intelligent reflecting surfaces (IRSs) or reconfigurable intelligent surfaces (RISs) typically entail the full channel state information (CSI). However, the computational cost of channel acquisition soars exponentially with the number of IRSs. To bypass this difficulty, we propose a novel strategy called blind beamforming that coordinates multiple IRSs by means of statistics without knowing CSI. Blind beamforming only requires measuring the received signal power at the user terminal for a sequence of randomly generated phase shifts across all IRSs. The main idea is to extract the key statistical quantity for beamforming by exploring only a small portion of the whole solution space of phase shifts. We show that blind beamforming guarantees a signal-to-noise ratio (SNR) boost of Theta(N^{2L}) under certain conditions, where L is the number of IRSs and N is the number of reflecting elements per IRS. The above result significantly improves upon the state of the art in the area of multi-IRS assisted communication. Moreover, blind beamforming is justified via field tests and simulations.

翻译：传统面向智能反射面（IRS）或可重构智能表面（RIS）的波束赋形方法通常需要完整的信道状态信息（CSI）。然而，随着IRS数量的增加，信道获取的计算成本呈指数级增长。为克服这一困难，我们提出一种名为"盲波束赋形"的新策略，该策略无需CSI即可通过统计方法协调多个IRS。盲波束赋形仅需在用户终端测量所有IRS上随机生成相位偏移序列对应的接收信号功率。其核心思想是通过仅探索整个相位偏移解空间的一小部分，提取用于波束赋形的关键统计量。我们证明，在特定条件下，盲波束赋形可保证信噪比（SNR）提升量达到Θ(N^{2L})，其中L为IRS数量，N为每个IRS的反射单元数。该结果显著优于多IRS辅助通信领域的最新成果。此外，通过现场测试和仿真验证了盲波束赋形的有效性。