Multiobjective Optimization of Wireless Powered Communication Networks Assisted by Intelligent Reflecting Surface Based on Multiagent Reinforcement Learning

Intelligent reflecting surface (IRS) is expected to be an important enabling technology for future wireless communication networks due to its capacity for reconfiguring wireless propagation environments. In this article, we consider a multiuser communication system for wireless powered communication network (WPCN) with IRS assistance. To overcome the low-quality communication problem of remote Internet of Things (IoT) devices in WPCN, we propose a multiobjective optimization scheme for IRS-assisted WPCN to optimize jointly throughput and remaining energy of remote IoT devices. We present a multiobjective optimization problem by jointly designing the hybrid access point (HAP) transmit beamforming, HAP receive beamforming, IRS phase shift beamforming, the IoT device transmit power, and energy-harvesting (EH)/information transmission (IT) time allocation to maximize system throughput and remaining energy. To address the aforementioned multiobjective optimization problem, the original optimization problem is first transformed into a Markov game model, and then, a multiobjective optimization scheme based on a multiagent deep deterministic policy gradient (MADDPG) is proposed. We centrally train the MADDPG model offline, and the two optimization objectives throughput and remaining energy are abstracted as two agents to execute decisions online. According to the results of the simulation, the multiobjective optimization scheme based on multiagent reinforcement learning can guarantee the performance of WPCN and enhance the throughput and remaining energy overall.