Intelligent reflecting surface (IRS) can be densely deployed in wireless networks to significantly enhance the communication channels. In this letter, we consider the downlink transmission from a multi-antenna base station (BS) to a single-antenna user, by exploiting the cooperative passive beamforming (CPB) and line-of-sight (LoS) path diversity gains of multi-IRS signal reflection. Unlike existing works where only one single multi-IRS reflection path from the BS to user is selected, we propose a new and more general multi-path beam routing scheme. Specifically, the BS sends the user's information signal via multiple orthogonal active beams (termed as active beam splitting), which point towards different IRSs. Then, these beamed signals are subsequently reflected by selected IRSs via their CPB in different paths, and finally coherently combined at the user's receiver (thus named {\it \textbf{passive beam combining}}). For this scheme, we formulate a new multi-path beam routing design problem to jointly optimize the number of IRS reflection paths, the selected IRSs for each of the reflection paths, the active/passive beamforming at the BS/each selected IRS, as well as the BS's power allocation over different active beams, so as to maximize the received signal power at the user. To solve this challenging problem, we first derive the optimal BS/IRS beamforming and BS power allocation for a given set of reflection paths. The clique-based approach in graph theory is then applied to solve the remaining multi-path selection problem efficiently. Simulation results show that our proposed multi-path beam routing scheme significantly outperforms its conventional single-path beam routing special case.
翻译:智能反射表面( IRS) 可以在无线网络中密集部署, 以大大增强通信频道。 具体地说, 我们考虑从多亚硝基站( BS) 向单一亚硝基站( BS) 发送用户信息信号, 利用多IRS 信号反射的合作性被动波束成形( CPB) 和直观( LOS) 路径多样性增益。 与目前只选择一个从 BS 到用户的多个多IRS 反射路径的工程不同, 我们提议了一个新的、 更普遍的多路径路程。 具体地说, BS 通过多个或远方的波纹基站将用户信息信号发送到一个单一的天线上, 然后, 这些信号随后通过多路径的 IP, 最终在用户接收器上一致地组合起来( 以 listitalbrobbbbbrick/ 组合起来) 。 对于这个方案, 我们制定了一个新的多路路径, 以 IMS 向多星流S 的多向多线流分配 的多路分配,, 以共同优化的图像 显示 的路径显示 的路径, 以共同优化的 以 IMS 优化的路径为 的 的, 以 以 优化的流 S 的 显示 的 的 的 以 以 最优化的 的 优化的 的 方向为 的 的 的 的 的 优化的 以, 方向为 以 的 优化的 优化的 向向向为 的 。