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 5th 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 multi-mode HAPS that can adaptively switch between 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 to other non-terrestrial systems, followed by an exposition of the different HAPS modes proposed. Subsequently, we illustrate the envisioned multi-mode HAPS, and discuss its benefits and challenges. Finally, we validate the multi-mode efficiency through a case study.

翻译：高空平台站（HAPS）概念近期受到工业界和学术界的广泛关注，以支持未来无线网络。HAPS可配备第五代（5G）及更先进技术，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将在农村和城市地区支持众多应用。然而，这伴随着高能耗和较短的滞空时间。为解决这一问题，我们设想采用一种多模式HAPS，能够自适应地在不同模式间切换以降低能耗并延长滞空时间。这些模式包括：用于增强计算、缓存和通信服务的HAPS超级宏基站（HAPS-SMBS）模式，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确保运行主要依赖被动通信载荷，仅在必要时切换到高能耗的主动模式。本文首先简要回顾HAPS相较于其他非地面系统的特性，随后阐述所提出的不同HAPS模式。接着，我们描绘所设想的的多模式HAPS，并讨论其优势与挑战。最后，通过案例研究验证多模式的效率。