Resource Allocation for Spectral Efficiency Maximization in WPCN-NOMA Systems with Multiple IRSs

Intelligent Reflecting Surface (IRS) is a prominent technology for wireless communications especially due to its capacity to enhance signal propagation based on the signal reconfiguration made by smart reflections. In this context, the investigation of the performance gains that can be obtained with the introduction of IRSs in Wireless Powered Communication Network (WPCN) has been a relevant research topic. In this article, we assume a Non-Orthogonal Multiple Access (NOMA)-based WPCN with multiple IRSs. In order to maximize the total transmitted data rate, we consider the optimization of IRSs' phase shifts and time duration for Downlink Wireless Power Transfer (DL WPT) phase and Uplink Wireless Information Transmission (UL WIT) phase of WPCN, as well as devices' transmit power. We proposed two different solutions based on Alternating Optimization (AO): centralized and distributed approaches. While the phase shifts of all IRSs are jointly optimized in the former, the phase shifts are independently defined for each IRS in the latter. In our simulation results, we show that increasing the number of IRSs in the system enhances the sum throughput and reduces the energy consumption. Furthermore, the centralized approach not only achieves higher throughput and lower energy consumption compared to the distributed one but also is more robust against the imperfect Channel State Information (CSI) issue than the distributed approach.