Robust Transmit and Reflect Beamforming Design for IRS-Assisted Offshore NOMA Communication Systems

We consider a non-orthogonal multiple access (NOMA) offshore communication system, where an intelligent reflecting surface (IRS) is deployed to assist the communication from a terrestrial base station (BS) to two ship users, and the channel state information (CSI) of the BS-user and BS-IRS channels is imperfect due to these channels' time-varying nature caused by wave fluctuation. By applying the bounded error model to describe the imperfect CSI, we conduct robust design on the BS's transmit beamforming and the IRS's reflect beamforming, which minimizes the BS's transmit power subject to the constraints of the users' minimum required data rates. An efficient alternating optimization algorithm based on the S-procedure, semidefinite programming, penalty, and successive convex approximation techniques has been proposed to solve the robust design problem. Furthermore, the proposed algorithm is extended to the case where the IRS has the reflecting element grouping capability. Simulation results show that the proposed algorithm can significantly reduce the BS's transmit power and guarantee the users' worst-case required data rates, as compared to other baseline algorithms.