Terahertz Multi-User Massive MIMO With Intelligent Reflecting Surface: Beam Training and Hybrid Beamforming

Terahertz (THz) communications open a new frontier for the wireless network thanks to their dramatically wider available bandwidth compared current micro-wave and forthcoming millimeter-wave communications. However, due short length of THz waves, they also suffer from severe path attenuation poor diffraction. To compensate THz-induced propagation loss, this paper proposes combine two promising techniques, viz., massive multiple input output (MIMO) intelligent reflecting surface (IRS), in multi-user communications, considering significant beamforming aperture gains. Nonetheless, channel estimation low-cost turn out be main obstacles realizing combination, passivity IRS sending/receiving pilot signals large-scale use expensive RF chains MIMO. In view these limitations, first develops cooperative beam training scheme facilitate with IRS. particular, we design different hierarchical codebooks proposed procedure, which are able balance between robustness against noise searching complexity. Based on results, further propose cost-efficient hybrid (HB) designs both single-user scenarios, respectively. Simulation results demonstrate that joint HB is achieve close performance optimal fully digital implemented even under perfect state information (CSI).