Max-Min Throughput Optimization in WPCNs: A Hybrid Active/Passive IRS-Assisted Scheme

The integration of wireless powered communication network (WPCNs) with intelligent reflecting surface (IRS) technology has emerged as a promising solution for enhancing the energy and spectral efficiency of the network. Recent studies have explored the benefits of active and passive reflecting element surfaces in various networks. However, most existing works on IRS-assisted WPCNs mainly focus on comparing an active IRS to single/multiple IRSs or to a hybrid IRS comprising active and passive elements on the same surface. In this paper, we explore a hybrid, active and passive IRS-assisted WPCN which can significantly improve network capacity. By introducing a distributed pair of active and passive IRSs, signal amplification and multiple reflection links can boost the wireless link capacity. To enhance network performance, this new framework utilizes both active and passive IRS elements to optimize wireless energy transfer (WET) on the downlink and wireless information transfer (WIT) on the uplink. However, designing a joint deployment of active and passive IRS elements becomes more challenging due to the joint operations of downlink WET and uplink WIT in WPCNs. To address the complexity of the non-convex optimization problem associated with the hybrid IRS-aided architecture, we use a systematic divide-and-conquer methodology. This decomposes the main problem into three interconnected sub-problems that are solved sequentially using sophisticated techniques. Furthermore, the study examines two practical deployment scenarios for active and passive IRS elements, namely 'Hybrid Case-1' (where active IRS is placed near the hybrid access point (H-AP) and passive IRS is placed near wireless devices) and 'Hybrid Case-2' (where active IRS is placed near wireless devices and passive IRS is placed near the H-AP). Extensive simulations and numerical analysis demonstrate the superiority of our proposed hybrid IRS-based framework over single active IRS and conventional double passive IRSs-assisted network, making it a promising and compelling solution for practical WPCN deployments, ensuring enhanced network performance and throughput fairness in wireless power and communications technologies.