10 11 12 13 the coverage hole problem was a reconfigurable intelligent 57 surface (RIS). A RIS, defined as an actively controlled meta-58 surface, can provide alternative wireless propagation paths 59 when new ones are required, as shown in Fig. 1. When 60 obstacles block the line-of-sight paths between the base sta-61 tion and user equipment, alternative paths can be provided 62 to users in the blocked area via the reflected signal at the 63 RIS. The RIS consists of uniformly distributed reconfigurable 64 unit cells with integrated switching devices (or components).

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