RIS-Assisted mmWave MIMO Communications With Finite-Alphabet Inputs and Partial CSI

A reconfigurable intelligent surface (RIS)-assisted transmission framework is proposed for millimeter wave (mmWave) multiple-input multiple-output systems having finite-alphabet input signals. To reduce signaling overhead, only partial channel state information (CSI), including the instantaneous CSI between the RIS and the base station (BS) as well as the statistical CSI between the user and the RIS, is exploited for asymptotic analyses of the ergodic mutual information (EMI). It is found that the EMI converges to some constant in the high-SNR regime and the rate of convergence is determined by the diversity order and the array gain. On this basis, an efficient algorithm is proposed to jointly design the passive beamformer of the RIS and the active beamformer of the BS to improve the array gain as well as the EMI. All the analytical results are verified by numerical results.