Optimization-Based Solution for Data Rate Maximization with QoS Guarantees for IRS-Aided NOMA-WPCN

In this article, we study an Intelligent Reflecting Surface (IRS)-aided Wireless Powered Communication Network (WPCN) composed of a Power Station (PS), an Access Point (AP), and several devices. In the first phase, devices collect energy in Downlink (DL) through Wireless Energy Transfer (WET) from PS, whereas in the second phase, they perform Wireless Information Transfer (WIT) in Uplink (UL) to the AP. During UL WIT, Non-Orthogonal Multiple Access (NOMA) is employed where the devices’ messages are decoded through Successive Interference Cancellation (SIC) at the AP. In this context, a problem is formulated with the objective of maximizing the total uplink data rate subject to individual Quality of Service (QoS) guarantees to the devices. To achieve that objective, the time duration for phases 1 and 2 as well as phase shifts of the IRS for WET and WIT are jointly optimized. The optimization problem is non-convex and very difficult to solve, therefore, we propose a solution based on Alternate Optimization (AO) which splits the problem into three new subproblems: 1) phases duration optimization; 2) phase shifts optimization for DL WET; 3) phase shifts optimization for UL WIT. In particular, numerical results show that the proposed solution outperforms benchmark solutions both in terms of maximizing data rates and reducing time duration in DL WET for different levels of QoS and number of IRS elements.