Abstract: Aiming at the high energy consumption problem that exists in multiple-input multiple-output C-IoT (Cognitive Internet of Things) systems, a joint beamforming optimization algorithm based on IRS(Intelligent Reflecting Surface) assistance is proposed. Taking the signal-to-interference-to-noise ratio at the secondary user and the discrete phase shift at the IRS as constraints, a new optimization criterion is constructed to maximize the energy efficiency of system by jointly optimizing the active beamforming matrix at the secondary transmitter and the passive beamforming matrix at the IRS. After decomposing the complex non-convex optimization problem into sub-problems, the fixed-point iteration method and the successive refinement method are used to process the sub- problems respectively. The simulation results show that the proposed algorithm has good convergence in multi- antenna scenarios. Compared to the baseline scheme, the proposed algorithm effectively improves the energy efficiency of the system in multi-user situations.

Key words: intelligent reflecting surface, discrete phase shift, beamforming optimization, energy efficiency