Channel Estimation for RIS-Aided Multiuser Millimeter-Wave Systems

Reconfigurable intelligent surface (RIS) is a promising device that can reconfigure the electromagnetic propagation environment through adjustment of phase shifts its reflecting elements. However, channel estimation in RIS-aided multiuser multiple-input single-output (MU-MISO) wireless communication systems challenging due to passive nature RIS and large number elements lead high overhead. To address this issue, we propose novel cascaded strategy with low pilot overhead by exploiting sparsity correlation channels millimeter-wave MISO systems. Based on fact physical positions BS, users do not appreciably change over multiple consecutive coherence blocks, first estimate full state information (CSI) including all angle gain block, then only re-estimate gains remaining blocks much lower In two-phase method, which one typical user estimated Phase I based linear among paths, while other are II utilizing reparameterized CSI common base station (BS)-RIS obtained I. The minimum less than existing works. Simulation results show performance proposed method outperforms methods terms accuracy when using same amount