Reconfigurable intelligent surfaces (RISs) have been introduced to improve the signal propagation characteristics by focusing the signal power in the preferred direction, thus making the communication environment 'smart'. The typical use cases and applications for the 'smart' environment include beyond 5G communication networks, smart cities, etc. The main advantage of employing RISs in such networks is a more efficient exploitation of spatial degrees of freedom. This advantage manifests in better interference mitigation as well as increased spectral and energy efficiency due to passive beam steering. Challenging environments (CEs) comprise a range of scenarios, which share the fact that it is extremely difficult to establish a communication link using conventional technology due to many impairments typically associated with the propagation medium and increased signal scattering. Although the challenges for the design of communication networks in such environments are known, there is no common enabler or solution for all these applications. Interestingly, the use of RISs in such scenarios can become such an enabler and a game changer technology. Surprisingly, the benefits of RIS for wireless networking in underwater and underground medium as well as in industrial and disaster environments have not been addressed yet. This paper aims at filling this gap by providing a motivation for the application of RISs in CEs. In addition, novel research challenges to be addressed in this context are discussed.

中文翻译：

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在具有挑战性的环境中可重新配置的智能曲面

已引入可重构智能表面（RIS），以通过将信号功率集中在首选方向来改善信号传播特性，从而使通信环境“智能”。“智能”环境的典型用例和应用包括5G通信网络，智慧城市等以外的地区。在此类网络中使用RIS的主要优势是对空间自由度的更有效利用。由于无源光束转向，这种优势体现在更好的干扰减轻以及频谱和能量效率的提高。具有挑战性的环境（CE）包含一系列场景，它们共享以下事实：由于通常与传播介质相关联的许多损害和增加的信号散射，因此使用常规技术建立通信链路极为困难。尽管在这样的环境中设计通信网络面临的挑战是众所周知的，但是对于所有这些应用程序都没有通用的实现器或解决方案。有趣的是，在这种情况下使用RIS可以成为这种推动者和改变游戏规则的技术。令人惊讶的是，RIS在水下和地下介质以及工业和灾难环境中的无线网络优势尚未得到解决。本文旨在通过提供将RIS应用于CE的动机来填补这一空白。另外，讨论了在这种情况下要解决的新颖研究挑战。