Autonomous reconfigurable intelligent surface (RIS) offers the potential to simplify deployment by reducing the need for real-time remote control between a base station (BS) and an RIS. However, we highlight two major challenges posed by autonomy. The first is implementation complexity, as autonomy requires hybrid RISs (HRISs) equipped with additional on-board hardware to monitor the propagation environment and conduct local channel estimation (CHEST), a process known as probing. The second challenge, termed probe distortion, reflects a form of the observer effect: during probing, an HRIS can inadvertently alter the propagation environment, potentially disrupting the operations of other communicating devices. While implementation complexity has been extensively studied, probe distortion remains largely unexplored. To further assess the potential of autonomous RISs, this paper comprehensively and pragmatically studies fundamental trade-offs posed by these challenges. We examine the robustness of an HRIS-assisted massive multiple-input multiple-output (mMIMO) system under minimal design choices that reflect the essential elements and stringent conditions, including (a) two extremes of implementation complexity realized through minimalist operational designs of two HRIS hardware architectures, and (b) an oblivious BS that fully embraces probe distortion. To make our analysis possible, we propose a physical-layer orchestration framework that aligns HRIS and mMIMO operations. We provide empirical evidence showing that autonomous RIS holds promise even under these strict conditions and propose new research directions, particularly for advancing the understanding of probe distortion.

翻译：自主可重构智能表面（RIS）通过减少基站（BS）与RIS之间实时远程控制的需求，为简化部署提供了潜力。然而，我们指出自主性带来的两大挑战。其一是实现复杂性，因为自主性需要混合RIS（HRIS）配备额外的板载硬件以监测传播环境并进行本地信道估计（CHEST），这一过程称为探测。第二个挑战称为探测失真，它反映了观察者效应的一种形式：在探测过程中，HRIS可能无意中改变传播环境，从而潜在地干扰其他通信设备的运行。虽然实现复杂性已得到广泛研究，但探测失真在很大程度上仍未得到探索。为了进一步评估自主RIS的潜力，本文全面且务实地研究了这些挑战带来的基本权衡。我们考察了HRIS辅助的大规模多输入多输出（mMIMO）系统在反映基本要素和严格条件的最小设计选择下的鲁棒性，包括：（a）通过两种HRIS硬件架构的极简操作设计实现实现复杂性的两个极端，以及（b）完全接受探测失真的无感知BS。为了使分析可行，我们提出了一个物理层编排框架，以协调HRIS和mMIMO操作。我们提供的实证证据表明，即使在上述严格条件下，自主RIS仍具有发展前景，并提出了新的研究方向，特别是为了推进对探测失真的理解。