This work focuses on wideband intelligent reflecting surface (IRS)-aided multiuser MIMO systems. One of the major challenges of this scenario is the joint design of the frequency-dependent base station (BS) precoder and user filters, and the IRS phase-shift matrix which is frequency flat and common to all the users. In addition, we consider that the channel state information (CSI) is imperfect at both the transmitter and the receivers. A statistical model for the imperfect CSI is developed and exploited for the system design. A minimum mean square error (MMSE) approach is followed to determine the IRS phase-shift matrix, the transmit precoders, and the receiving filters. The broadcast (BC)- multiple access channel (MAC) duality is used to solve the optimization problem following an alternating minimization approach. Numerical results show that the proposed approach leads to substantial performance gains with respect to baseline strategies that neglect the inter-user interference and do not optimize the IRS phase-shift matrix. Further performance gains are obtained when incorporating into the system design the statistical information of the channel estimation errors.

翻译：本文研究宽带智能反射面(IRS)辅助的多用户MIMO系统。该场景的主要挑战之一在于联合设计频率相关的基站(BS)预编码器与用户滤波器，以及频率平坦且对所有用户共用的IRS相移矩阵。此外，我们考虑发射端和接收端的信道状态信息(CSI)均不完善。本文建立并利用不完全CSI的统计模型进行系统设计。采用最小均方误差(MMSE)方法确定IRS相移矩阵、发射预编码器和接收滤波器。利用广播信道(BC)-多址接入信道(MAC)对偶性，通过交替最小化方法求解优化问题。数值结果表明，与忽略用户间干扰且不优化IRS相移矩阵的基准策略相比，所提方法可带来显著的性能提升。将信道估计误差的统计信息纳入系统设计后，可获得进一步的性能增益。