关键词: 无线协能通信网络, 智能反射面, 资源分配, 时分多址技术, 能量效率, Dinkelbach方法, 半正定规划方法

Abstract: Aiming at the problems of small coverage area and easy to be blocked by obstacles in Wireless Powered Communication Network (WPCN), the resource allocation of Intelligent Reflective Surface (IRS)assisted relaying in WPCN systems under communication blocking conditions was investigated. Specifically, in the downlink, IRS was used to assist users to collect energy from the Hybrid Access Point (HAP); in the uplink, IRS was used to assist users to send information to the HAP. Considering that the system contains both energy transmission and information transmission, the Time Division Multiple Access (TDMA) was used to divide the energy collection, the data communication, and the data relay transmission. Based on the constructed system model and transmission strategy, the energy efficiency optimisation problem was proposed with the constraints of user's quality of service and the energy consumed by the user to send information.The total energy efficiency of the system was maximised by jointly optimising the sending power, IRS phase shift matrix and time scheduling. Due to the non-convex nature of the proposed problem, the fractional form of the objective function was first converted to a non-fractional form using Dinkelbach's method, then the non-convex problem was converted to a convex problem using variable substitution and Semi-Definite Programming (SDP), and finally the suboptimal solution of the optimisation problem was obtained using CVX. Simulation results show that the proposed scheme not only extends the coverage of this system, but also effectively improves the energy efficiency of the system. Compared with the average allocation time scheme and the use of hybrid relay nodes, the proposed scheme improves the system energy efficiency by 12.43% and 30.46% on average.

Key words: Wireless Powered Communication Network(WPCN), Intelligent Reflecting Surface(IRS), resource allocation, Time Division Multiple Access(TDMA), energy efficiency, Dinkelbach method, Semi-Definite Programming(SDP)