Cooperative Reflection Design With Timing Offsets in Distributed Multi-RIS Communications

• Published in: IEEE wireless communications letters Vol. 10; no. 11; pp. 2379 - 2383
• Main Authors: Zhao, Yaqiong, Xu, Wei, Sun, Huan, Ng, Derrick Wing Kwan, You, Xiaohu
• Format: Journal Article
• Language: English
• Published: Piscataway IEEE 01.11.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Channel estimation; Closed form solutions; Equalizers; Exact solutions; majorization-minimization; Mathematical analysis; multi-node synchronization; Offsets; Pulse shaping methods; Reconfigurable intelligent surface (RIS); Reflection; Simulation; Sun; Synchronism; Synchronization; timing offset; Wireless communication; Wireless communication systems
• ISSN: 2162-2337; 2162-2345
• DOI: 10.1109/LWC.2021.3100989

This letter investigates a wireless communication system deploying distributed reconfigurable intelligent surfaces (RISs). Existing works have assumed that perfect timing synchronization is available among all the cooperative RISs. For practical considerations, we first study cooperative reflection design for multi-RIS-aided communication systems taking into account timing synchronization errors. We aim to minimize the mean-squared error of the recovered data in the presence of timing offsets subject to the unit-modulus constraints imposed on the phase shifts of the RISs. In order to handle this sophisticated nonconvex problem, we develop a computationally-efficient algorithm based on the majorization-minimization framework where the RIS phase shift matrices and the timing offset equalizer are respectively developed in a semi-closed form and a closed form. Numerical examples validate the improved performance of our proposed design compared with various schemes.