Alternating Minimization for the Downlink of Wideband IRS-Aided mmWave MIMO Systems

We consider an orthogonal frequency division multiplexing (OFDM) intelligent reflecting surface (IRS)-aided millimeter-wave (mmWave) multiple-input multipleoutput (MIMO) broadcast (BC) system. The IRS phase-shift matrix, the filters, and the precoders are jointly designed to minimize the mean square error (MSE) of the estimated user symbols. This is challenging because the IRS phase-shift matrix is frequency-flat and common to all the users. The optimization problem is solved via the BC-multiple access channel (MAC) duality and following an alternating minimization approach. The results show that the proposed approach leads to large gains with respect to baseline strategies that do not account for the inter-user interference.