The advent of the fifth-generation (5G) technology has revolutionized the way we think about communication networks, enabling a plethora of new use cases and scenarios that were not possible with previous generations of wireless technology. The existing 5G communication networks predominantly rely on terrestrial communication infrastructure, which, however, exhibits several notable limitations such as capacity constraints, latency issues, and energy inefficiencies, necessitating this next-generation leap. The 6G aims to provide a comprehensive solution for a hyperconnected, intelligent, and immersive digital ecosystem, seamlessly integrating terrestrial, airborne, and spaceborne networks which is referred to as the space-air-ground-sea integrated network (SAGSIN). A traditional SAGSIN scenario mainly includes 3 segments: spaceborne network, airborne network, and terrestrial network. The classical SAGSIN architecture has shown remarkable capabilities in providing massive connectivity by integrating spaceborne, airborne, and terrestrial cellular networks, which, however, encounters inherent technical challenges against their respective practical implementation. On the other hand, the philosophy of near-space communications (NS-COM) is gradually emerging. The distinctive location of near space which is 20 ~ 100 km above Earth’s surface positiones at the core of the SAGSIN, thus allowing the NS-COM network to address the shortcomings of traditional spaceborne, terrestrial, and airborne networks. NS-COM present a promising addition to SAGSIN, making them the final piece of the SAGSIN puzzle.
