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Energy-Efficient Wireless Communications with Distributed Reconfigurable Intelligent Surfaces

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Zhaohui Yang, Mingzhe Chen, Walid Saad, Wei Xu, Mohammad Shikh-Bahaei, H. Vincent Poor, Shuguang Cui

Bibliographical note

Funding Information: This work was supported in part by the U.S. National Science Foundation under Grant 2030215, Grant CNS-1836802, and Grant CNS-1909372; in part by the Engineering and Physical Sciences Research Council (EPSRC) Scalable Full Duplex Dense Wireless Networks (SENSE) Project under Grant EP/P003486/1; in part by the NSFC under Grant 62022026; in part by the Natural Science Foundation of Jiangsu Province for Distinguished Young Scholars under Grant BK20190012; in part by the Fundamental Research Funds for the Central Universities under Grant 2042021kf1030; and in part by EPSRC Internet of Silicon Retinas (IoSIRE) Project under Grant EP/P022723/1. Publisher Copyright: IEEE

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This paper investigates the problem of resource allocation for a wireless communication network with distributed reconfigurable intelligent surfaces (RISs). In this network, multiple RISs are spatially distributed to serve wireless users and the energy efficiency of the network is maximized by dynamically controlling the on-off status of each RIS as well as optimizing the reflection coefficients matrix of the RISs. This problem is posed as a joint optimization problem of transmit beamforming and RIS control, whose goal is to maximize the energy efficiency under minimum rate constraints of the users. To solve this problem, two iterative algorithms are proposed for the singleuser case and multi-user case. For the single-user case, the phase optimization problem is solved by using a successive convex approximation method, which admits a closed-form solution at each step. Moreover, the optimal RIS on-off status is obtained by using the dual method. For the multi-user case, a low-complexity greedy searching method is proposed to solve the RIS on-off optimization problem. Simulation results show that the proposed scheme achieves up to 33% and 68% gains in terms of the energy efficiency in both single-user and multi-user cases compared to the conventional RIS scheme and amplify-and-forward relay scheme, respectively.

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