Abstract: This paper studies the optimization of wireless powered communication network assisted by intelligent reflecting surface (IRS). In order to improve the overall transmission rate of the system while guaranteeing the fairness of user service, beamforming, time allocation, user transmission power and IRS phase shift are jointly optimized to maximize the minimum user transmission rate. The original optimization problem is a multi-variable non-convex problem, which is transformed by introducing slack variables and using semi-definite relaxation. Then, the transformed problem is solved by using the method including golden section search, successive convex approximation and alternate iterative optimization. The simulation results show that compared with the optimization scheme aiming at the maximum sum rate, the proposed optimization algorithm can obtain a significantly higher minimum user rate, and the service fairness among users is significantly improved. Compared with the scheme without IRS, which maximize the minimum user rate, both the minimum user rate and the sum rate are higher, and the performance advantage increases with the increase of the number of IRS units in our proposed scheme, which shows that IRS can effectively improve the energy and information transmission efficiency.

Key words: intelligent reflecting surface (IRS), wireless powered communication network (WPCN), minimum rate maximization, beam forming