IEEE TRANSACTIONS ON GREEN COMMUNICATIONS AND NETWORKING, VOL. 6, NO. 1, MARCH 2022 175 Exploiting Benefits of IRS in Wireless Powered NOMA Networks Xingwang Li , Senior Member, IEEE, Zhen Xie, Zheng Chu , Member, IEEE, Varun G. Menon , Senior Member, IEEE, Shahid Mumtaz , Senior Member, IEEE, and Jianhua Zhang , Senior Member, IEEE Abstract—We consider an intelligent reflecting surface (IRS) wireless-powered NOMA Internet-of-Things (IoT) network, where multiple NOMA IoT devices can communicate with access point (AP) with the aid of IRS. Specifically, IoT devices can harvest energy from a nearby appropriative power station (PS) during the wireless energy transfer (WET) phase through the direct links as well as the reflecting links from IRS. Then, the harvested energy can achieve the wireless information trans- fer (WIT) during the uplink between IoT devices and AP by adopting NOMA protocol. A novel resource allocation scheme is proposed to maximized the sum throughput of the consid- ered system by jointly optimizing the time allocation factor and phase shift matrices of WET and WIT. The optimization problem is non-convex due to multiple variables. We first transfer this problem into convex function by assuming one of the phase shift matrices fixed, and solve the transferred problem by obtaining closed-form solution. Then, the elements collaborative approxi- mate (ECA) and the manifold space gradient descent (MSGD) algorithms are designed to optimize the phase shift matrix. ECA is iteratively optimizing one element and MSGD is focus on the derivation of a gradient descent over the manifold space. Numerical results indicate the sum throughput enhancement by IRS compared with no IRS, and highlight the advantages of IRS. Index Terms—Intelligent reflecting surface (IRS), non- orthogonal multiple access (NOMA), Internet of Things (IoT). Manuscript received June 9, 2021; revised December 27, 2021; accepted January 16, 2022. Date of publication January 20, 2022; date of current ver- sion February 16, 2022. This work was supported in part by the National Natural Science Foundation of China under Grant 92167202; in part by the Key project of Guizhou Science and Technology Support Program under Grant Guizhou Key Science and Support [2021]- 001; in part by the Open Foundation of State key Laboratory of Networking and Switching Technology (Beijing University of Posts and Telecommunications) under Grant SKLNST- 2021-1-21; and in part by the Intelligent and Sustainable Aerial-Terrestrial IoT Networks-BATS under Grant PTDC/EEI-TEL/1744/2021. (Corresponding author: Xingwang Li.) Xingwang Li and Zhen Xie are with the School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo 454000, China (e-mail: lixingwang@hpu.edu.cn; 311622020210@home.hpu.edu.cn). Zheng Chu is with the 5GIC & 6GIC, Institute for Communication Systems, University of Surrey, Guildford GU2 7XH, U.K. (e-mail: andrew.chuzheng7@gmail.com). Varun G. Menon is with the Department of Computer Science and Engineering, SCMS School of Engineering and Technology, Ernakulam 683576, India (e-mail: varunmenon@ieee.org). Shahid Mumtaz is with the Instituto de Telecomunicações, 3810078 Aveiro, Portugal (e-mail: smumtaz@av.it.pt). Jianhua Zhang is with the State Key Laboratory of Networking and Switching Technology, Beijing University of Posts and Telecommunications, Beijing 100876, China (e-mail: jhzhang@bupt.edu.cn). Digital Object Identifier 10.1109/TGCN.2022.3144744 I. I NTRODUCTION I NTERNET-OF-THINGS (IoT) technology is indispensable to the beyond fifth-generation (B5G) by delivering spec- ified functions through connecting devices or “things” over the mobile Internet, which can greatly improve the access rate of mass devices [1]–[3]. The IoT has another advantage to connect a huge number of devices for information transfer and/or exchange [4]. As one of the core components of the IoT network, machine-type communication (MTC) devices are assumed to be maintained without manual operation [5]. The sensors of IoT are designed with low power and always be powered by the batteries [6]. Therefore, this needs to peri- odic maintenance or change batteries to prolong their service time [7]. However, to face various applications of IoT, sensors will be deployed any scenarios, such as deployed in hospital to detect temperature and humidity [8], as well as can be worn by people to monitor their environments and physical charac- teristics in real time [9]. To this end, it is urgent to prolong lifetime of senors, but with limitations of battery technology, it is still an open problem [10]–[12]. Intelligent reflecting surface (IRS) is considered as one promising technology for B5G communication networks, which can intelligently promote the sum throughput of IoT [13]–[15]. The advantages of IRS are as follows: 1) By deploying a mass of IRS reflecting elements with low power, the disruptive revolution of IRS is that it can enable wireless reflection state reconfiguration by changing phase or ampli- tude according to the actual situation [16]–[18]; 2) Small size and low cost elements are deployed, where the signal can be efficiently and flexibly reflected form multiple beam without the dedicated radio frequency (RF) components [19]; 3) IRS can achieve signal coverage, that is, when there is a bar- rier to direct communication, IRS can be deployed to reflect signals for wireless communication [20]; 4) IRS can also change channel propagation condition by controlling the phase of reflecting elements, thereby improving the performance of wireless communication systems, such as energy efficiency, sum-throughput, etc. [21]–[23]; 5) In terms of physical deploy- ment, IRS has the features of small and light which make it easy to be attached to or removed from walls, which make it very simple for actual deployment [24]. In light of this fact, a comparison of IRS with classical decode and forward relays showed the superiority of IRS [25]. Finally, the security and reliability can be improved by superimposition of reflected signals of IRS and other path signals [26]. 2473-2400 c  2022 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See https://www.ieee.org/publications/rights/index.html for more information. Authorized licensed use limited to: Henan Polytechnic University. Downloaded on July 28,2022 at 08:05:27 UTC from IEEE Xplore. Restrictions apply.