Cooperative Beam Routing for Multi-IRS Aided Communication

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