标题： 多IRS辅助通信的协作波束路由 显示英文标题

标题： Cooperative Beam Routing for Multi-IRS Aided Communication

摘要： 智能反射表面（IRS）被认为是一种变革性技术，用于实现无线通信中的智能和可重构环境。 这封信研究了一个新的IRS辅助通信系统，其中多个IRS通过多跳信号反射协助多天线基站（BS）与远程单天线用户之间的通信。 具体而言，通过利用附近IRS之间的视距（LoS）链路，建立BS和用户之间的多跳级联LoS链路，选择一组IRS依次反射BS的信号，以使用户处的接收信号功率最大化。 为解决这一新问题，我们首先为给定的波束路由分别给出了BS和选定IRS上最优主动和协作被动波束成形的闭式解。 然后，我们推导了端到端信道功率，揭示了在最优波束路由设计中最大化乘法被动波束成形增益与最小化多反射路径损耗之间的基本权衡。 为了调和这一权衡，我们将IRS选择和波束路由问题重新表述为图论中的等效最短简单路径问题，并对其进行最优求解。 数值结果表明，所提出的算法相对于基准方案具有显著的性能优势，并对最优波束路由设计提供了有用的见解。 显示英文摘要

摘要： Intelligent reflecting surface (IRS) has been deemed as a transformative technology to achieve smart and reconfigurable environment for wireless communication. This letter studies a new IRS-aided communication system, where multiple IRSs assist in the communication between a multi-antenna base station (BS) and a remote single-antenna user by multi-hop signal reflection. Specifically, by exploiting the line-of-sight (LoS) link between nearby IRSs, a multi-hop cascaded LoS link between the BS and user is established where a set of IRSs are selected to successively reflect the BS's signal, so that the received signal power at the user is maximized. To tackle this new problem, we first present the closed-form solutions for the optimal active and cooperative passive beamforming at the BS and selected IRSs, respectively, for a given beam route. Then, we derive the end-to-end channel power, which unveils a fundamental trade-off in the optimal beam routing design between maximizing the multiplicative passive beamforming gain and minimizing the multi-reflection path loss. To reconcile this trade-off, we recast the IRS selection and beam routing problem as an equivalent shortest simple-path problem in graph theory and solve it optimally. Numerical results show significant performance gains of the proposed algorithm over benchmark schemes and also draw useful insights into the optimal beam routing design.