Intelligent Reflecting Surface-Aided Wireless Networks: From Single-Reflection to Multireflection Design and Optimization

Intelligent reflecting surface (IRS) has emerged as a promising technique for wireless communication networks. By dynamically tuning the reflection amplitudes/phase shifts of large number passive elements, IRS enables flexible channel control and configuration thereby enhances signal transmission rate reliability significantly. Despite vast literature on designing optimizing assorted IRS-aided systems, prior works have mainly focused enhancing links with single only by one or multiple IRSs, which may be insufficient to boost link capacity under some harsh propagation conditions (e.g., indoor environment dense blockages/obstructions). This issue can tackled employing two more IRSs assist each jointly exploiting their well reflections over them. However, resultant double-/multi-IRS-aided systems face complex design issues new practical challenges implementation compared conventional single-IRS counterpart, in terms optimization, acquisition, deployment association/selection. As such, paradigm multi-IRS cooperative beamforming joint active/passive beam routing arises, calls innovative approaches optimization methods. In this article, we give tutorial overview multi-IRS-aided networks, an emphasis addressing due routing. Moreover, point out important directions worthy research investigation future.