This letter considers the communication between a multiple antenna Base Station (BS) and a single antenna user, assisted by an Intelligent Reflecting Surface (IRS). Due to the large number of elements at the IRS, acquiring Channel State Information (CSI) requires many radio-frequency chains and considerable training overhead, what is limiting in practice. We aim to optimize the beamforming at the BS and IRS without CSI, by minimizing the transmit power, subject to a minimum signal-to-noise ratio (SNR). To solve this problem, a new method based on the Particle Swarm Optimization (PSO) technique is proposed. Results show that the new solution achieves similar performance as that of the optimal beamforming with CSI.

中文翻译：

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无CSI智能反射面的波束成形优化

这封信考虑了由智能反射面 (IRS) 辅助的多天线基站 (BS) 和单天线用户之间的通信。由于 IRS 有大量元素，获取信道状态信息 (CSI) 需要许多射频链和相当大的训练开销，这在实践中是有限的。我们的目标是在没有 CSI 的情况下优化 BS 和 IRS 的波束成形，通过最小化发射功率，受制于最小信噪比 (SNR)。为了解决这个问题，提出了一种基于粒子群优化（PSO）技术的新方法。结果表明，新解决方案实现了与使用 CSI 的最佳波束成形相似的性能。