In this letter, we consider an intelligent reflecting surface (IRS)-assisted multiuser communication system, where an IRS is deployed to provide virtual line-of-sight (LoS) links between an access point (AP) and multiple users. We consider the practical codebook-based IRS passive beamforming and study efficient design for IRS reflect beam training, which is challenging due to the large number of IRS reflecting elements. In contrast to the conventional single-beam training, we propose a new multi-beam training method by dividing the IRS reflecting elements into multiple sub-arrays and designing their simultaneous multi-beam steering over time. By simply comparing the received signal power over time, each user can detect its optimal IRS beam direction with a high probability, even without searching over all possible beam directions as the single-beam training. Simulation results show that our proposed multi-beam training significantly reduces the training time of conventional single-beam training and yet achieves comparable IRS passive beamforming performance for data transmission.

中文翻译：

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用于 IRS 辅助多用户通信的快速波束训练

在这封信中，我们考虑了智能反射面 (IRS) 辅助多用户通信系统，其中部署了 IRS 以在接入点 (AP) 和多个用户之间提供虚拟视距 (LoS) 链接。我们考虑了实用的基于码本的 IRS 无源波束成形，并研究了 IRS 反射波束训练的有效设计，由于 IRS 反射元件数量众多，这具有挑战性。与传统的单波束训练相比，我们提出了一种新的多波束训练方法，将 IRS 反射元件划分为多个子阵列，并随着时间的推移设计它们的同步多波束转向。通过简单地比较接收信号功率随时间的变化，每个用户都可以高概率检测到其最佳 IRS 波束方向，即使没有像单波束训练那样搜索所有可能的波束方向。仿真结果表明，我们提出的多波束训练显着减少了传统单波束训练的训练时间，同时实现了可比的 IRS 被动波束成形性能用于数据传输。