Abstract: The intelligent reflecting surface (IRS) is considered a core technology of next-generation mobile communication. It has significant advantages in enhancing network coverage, spectrum efficiency, energy efficiency, and deployment cost. The aerial intelligent reflecting surface (AIRS), which combines the high mobility of the air platform and the high-quality link characteristics provided by the intelligent reflecting surface, can effectively assist the transmission from the base station to the users in complex communication scenarios and enhance the network coverage. A joint optimization problem of the transmit beamforming, as well as the placement and passive beamforming for the AIRS was studied for AIRS assisted multi-user massive multiple input multiple output (MIMO) systems. Under the condition that the statistical channel state information (CSI) is known, an optimization scheme of system ergodic sum rate based on block coordinate descent (BCD) was proposed. Firstly, an optimization model was established by jointly optimizing the transmit beamforming at base station, the placement and the passive beamforming for AIRS. Secondly, the nonconvex optimization problem was decoupled into three subproblems that are easy to deal with by BCD descent algorithm. Finally, Lagrange multiplier method, relaxation variable method and RMSProp gradient descent algorithm were used to solve the subproblems respectively. The simulation results show that the proposed optimization scheme can effectively improve the ergodic sum rate of the system with good convergence properties.

Key words: Massive MIMO, Aerial intelligent reflecting surface, Statistical CSI, Location optimization, Beam forming