Path Loss in Reconfigurable Intelligent Surface-Enabled Channels
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A reconfigurable intelligent surface (RIS) employs an array of individually-controllable elements to scatter incident signals in a desirable way; for example, to facilitate links between base stations and mobile users that would otherwise be blocked by terrain. Models used to analyze RIS-enabled links in wireless networks are commonly rudimentary; typically considering only the number of elements and omitting considerations such as the physical dimensions of the RIS and the radiation pattern and spacing of constituent elements. This paper presents a simple yet broadly-applicable physical model for the RIS-enabled channel that accounts for these factors. This model is then used to analyze the path loss of channels enabled by a reflectarray-type RIS, yielding insights into performance as a function of the size of the RIS, proximity of the RIS to the transmitter and receiver, and the criteria used to control the elements. Path loss is compared to that of a free space (i.e., no RIS) channel having equal path length, and the conditions required for path loss equal to this benchmark are identified.
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