Realizing the wireless environmental sensing is another desired function of reconfigurable intelligent surface (RIS), in addition to enhancing the performance of wireless communication systems. In this paper, we design a holographic RIS-aided computational imaging system, which consists of a transmitter, a holographic RIS, a rectangular target and a receiver. Here, the target is composed of a series of discrete segments, each of which possesses a constant scattering density. The sensing task of the proposed system is to estimate the scattering densities of the target, which corresponds to the term computational imaging. The term holographic means that the RIS is modeled as a physically continuous surface with a physically continuous phase shift pattern, which can be approximately considered as having massive (possibly infinite) number of elements within a finite space. Both the RIS and the target are subject to the electromagnetic boundary conditions, whose scattered fields are computed by the equivalent current method and the physical equivalent. Based on the computed scattered fields of the target, we derive the pathloss of the proposed system. In order to perform the imaging, we alter the phase shift pattern of the RIS such that the main energy of its scattered fields is focused towards different segments of the target successively, which then produces multiple measurements of the scattering densities and simultaneously ensures a low pathloss. After all measurements are completed, the scattering densities of the target can be estimated with the observed measurement vector and the reconstructed sensing channel, i.e., the computational imaging is accomplished. Simulation results show that the proposed imaging strategy performs well if the system parameters are designed properly.

中文翻译：

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全息 RIS 计算成像：传感原理和路径损耗分析


除了增强无线通信系统的性能之外，实现无线环境传感是可重构智能表面（RIS）的另一个期望功能。在本文中，我们设计了一种全息RIS辅助计算成像系统，该系统由发射器、全息RIS、矩形目标和接收器组成。这里，目标由一系列离散的部分组成，每个部分都具有恒定的散射密度。该系统的传感任务是估计目标的散射密度，这对应于术语计算成像。全息一词意味着 RIS 被建模为具有物理连续相移图案的物理连续表面，可以近似认为在有限空间内具有大量（可能无限）的元素。 RIS和目标均受到电磁边界条件的影响，其散射场通过等效电流法和物理等效法计算。根据计算出的目标散射场，我们推导出所提出系统的路径损耗。为了进行成像，我们改变了 RIS 的相移模式，使其散射场的主要能量连续聚焦到目标的不同部分，然后产生散射密度的多次测量，同时确保低路径损耗。当所有测量完成后，可以利用观测到的测量向量和重建的传感通道来估计目标的散射密度，即完成计算成像。 仿真结果表明，如果系统参数设计得当，所提出的成像策略效果良好。