The high-altitude platform station (HAPS) concept has recently received notable attention from both industry and academia to support future wireless networks. A HAPS can be equipped with fifth-generation (5G) and beyond technologies such as massive multiple-input multiple-output (MIMO) and reconfigurable intelligent surface (RIS). Hence, it is expected that HAPS will support numerous applications in both rural and urban areas. However, this comes at the expense of high energy consumption and thus shorter loitering time. To tackle this issue, we envision the use of a multimode HAPS that can adaptively switch among different modes so as to reduce energy consumption and extend the HAPS loitering time. These modes comprise a HAPS super macro base station (HAPS-SMBS) mode for enhanced computing, caching, and communication services; a HAPS relay station (HAPS-RS) mode for active communication; and a HAPS-RIS mode for passive communication. This multimode HAPS ensures that operations rely mostly on the passive communication payload, while switching to an energy-greedy active mode only when necessary. In this article, we begin with a brief review of HAPS features compared with other nonterrestrial systems, followed by an exposition of the different HAPS modes proposed. Subsequently, we illustrate the envisioned multimode HAPS and discuss its benefits and challenges. Finally, we validate the multimode efficiency through a case study.

中文翻译：

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下一代无线网络多模高空平台站：选择机制、优势和潜在挑战

高空平台站（HAPS）概念最近受到业界和学术界的高度关注，以支持未来的无线网络。HAPS 可配备第五代 (5G) 及更高技术，例如大规模多输入多输出 (MIMO) 和可重构智能表面 (RIS)。因此，预计 HAPS 将支持农村和城市地区的众多应用。然而，这是以高能耗和更短的徘徊时间为代价的。为了解决这个问题，我们设想使用多模式 HAPS，它可以在不同模式之间自适应切换，从而降低能耗并延长 HAPS 徘徊时间。这些模式包括 HAPS 超级宏基站 (HAPS-SMBS) 模式，用于增强计算、缓存、和通讯服务；用于主动通信的HAPS中继站（HAPS-RS）模式；以及用于被动通信的 HAPS-RIS 模式。这种多模式 HAPS 确保操作主要依赖于无源通信有效负载，同时仅在必要时才切换到耗能的主动模式。在本文中，我们首先简要回顾一下 HAPS 与其他非地面系统相比的特点，然后阐述所提出的不同 HAPS 模式。随后，我们阐述了设想的多模式 HAPS 并讨论了其优点和挑战。最后，我们通过案例研究验证了多模效率。仅在必要时才切换到耗能主动模式。在本文中，我们首先简要回顾一下 HAPS 与其他非地面系统相比的特点，然后阐述所提出的不同 HAPS 模式。随后，我们阐述了设想的多模式 HAPS 并讨论了其优点和挑战。最后，我们通过案例研究验证了多模效率。仅在必要时才切换到耗能主动模式。在本文中，我们首先简要回顾一下 HAPS 与其他非地面系统相比的特点，然后阐述所提出的不同 HAPS 模式。随后，我们阐述了设想的多模式 HAPS 并讨论了其优点和挑战。最后，我们通过案例研究验证了多模效率。