This paper considers the massive connectivity with the aid of a reconfigurable intelligent surface (RIS), where an enormous number of devices transmit sporadically to a base station (BS). The RIS establishes favorable signal propagation environments to enhance data transmission in massive connectivity in such a scenario. Nevertheless, the BS needs to detect active devices and estimate channels to support data transmission in RIS-assisted massive access systems. Furthermore, due to a large number of devices, it is impossible to assign orthogonal signature sequences to the devices as in most of the existing works on RIS-related channel estimation, which yields unique challenges. This paper shall consider a RIS-assisted uplink IoT network and solve the RIS-related activity detection and channel estimation problem. The BS detects the active devices and estimates the separated channels of the RIS-to-device link and the RIS-to-BS link by using non-orthogonal pilot sequences. Due to limited scattering between the RIS and the BS, we model the RIS-to-BS channel as a sparse channel. As a result, by simultaneously exploiting both the sparsity of sporadic transmission in massive connectivity and the RIS-to-BS channels, we formulate the RIS-related activity detection and channel estimation problem as a sparse matrix factorization problem. Furthermore, we develop an approximate message passing (AMP) based algorithm to solve the problem based on the Bayesian inference framework and reduce the computational complexity by approximating the algorithm with the central limit theorem and Taylor series expansion. Finally, extensive numerical experiments are conducted to verify the effectiveness of the proposed algorithm.

中文翻译：

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用于大规模连接的可重构智能表面：联合活动检测和信道估计

本文考虑了借助可重构智能表面 (RIS) 的大规模连接，其中大量设备偶尔向基站 (BS) 传输。RIS 建立了有利的信号传播环境，以在这种情况下增强海量连接中的数据传输。然而，BS需要检测活动设备并估计信道以支持RIS辅助的海量接入系统中的数据传输。此外，由于设备数量众多，不可能像大多数现有的 RIS 相关信道估计工作那样为设备分配正交签名序列，这产生了独特的挑战。本文将考虑一个 RIS 辅助的上行物联网网络并解决RIS相关的活动检测和信道估计问题。BS通过使用非正交导频序列来检测活动设备并估计RIS-to-device链路和RIS-to-BS链路的分离信道。由于 RIS 和 BS 之间的散射有限，我们将 RIS 到 BS 通道建模为稀疏通道。因此，通过同时利用大规模连接中零星传输的稀疏性和 RIS 到 BS 信道，我们将与 RIS 相关的活动检测和信道估计问题表述为稀疏矩阵分解问题。此外，我们开发了一种基于近似消息传递 (AMP) 的算法来解决基于贝叶斯推理框架的问题，并通过使用中心极限定理和泰勒级数展开近似算法来降低计算复杂度。