Cooperative Multi-RIS Communications for Wideband mmWave MISO-OFDM Systems

Reconfigurable intelligent surfaces (RISs) can shape the wireless environment for enhancing communication performance. In this letter, we propose a cooperative multi-RIS assisted transmission scheme millimeter-wave multi-antenna orthogonal frequency division multiplexing system. We first put forward delay matching based simultaneously estimating multipath channels and delays of distributed RISs, which requires limited training overhead feedback. Based on scheme, obtain closed-form solution RIS phase shift. Then, derive an analytical expression downlink rate, is proved to increase logarithmically with square number reflecting elements. Simulations are conducted verify these observations.