The performance characterization of communication systems assisted by large reconfigurable intelligent surfaces (RISs) significantly depends on the adopted models for the underlying channels. Under unrealistic channel models, the system performance may be over- or under-estimated which yields inaccurate conclusions for the system design. In this paper, we review five channel models that are chosen to progressively improve the modeling accuracy for large RISs. For each channel model, we highlight the underlying assumptions, its advantages, and its limitations. We compare the system performance under the aforementioned channel models using RIS configuration algorithms from the literature and a new scalable algorithm proposed in this paper specifically for the configuration of extremely large RISs.

翻译：在不切实际的频道模型下,系统性能可能高估或低估,为系统设计得出不准确的结论;在本文件中,我们审查了为逐步提高大型RIS的模型准确性而选择的五个频道模型;对于每一个频道模型,我们强调基本假设、其优点及其局限性;我们利用文献中的RIS配置算法和本文件中专门为极大型RIS配置而提出的新的可扩展算法,比较上述频道模型下的系统性能。