Nonterrestrial Communications Assisted by Reconfigurable Intelligent Surfaces

Nonterrestrial communications have emerged as a key enabler for seamless connectivity in the upcoming generation networks. This kind of network can support high data rate among aerial platforms (i.e., unmanned vehicles (UAVs), high-altitude (HAPs), and satellites) cellular networks, achieving anywhere anytime connections. However, there are many practical implementation limitations, especially overload power consumption, probability blockage, dynamic propagation environment. Fortunately, recent technology reconfigurable intelligent surface (RIS) is expected to be one most cost-efficient solutions address such issues. RIS with low-cost elements bypass blockages create multiple line-of-sight (LoS) links provide controllable communication channels. In this article, we present comprehensive literature review on RIS-assisted nonterrestrial networks (RANTNs). First, framework RANTNs introduced detailed discussion about distinct properties NTNs two deployment types RIS, that is, terrestrial RISs (TRISs), (ARISs), classification RANTNs, including air-to-ground (A2G)/ground-to-air (G2A), ARIS-assisted ground-to-ground (G2G), air-to-air (A2A) communications. combination next-generation technologies, advanced technologies discussed. Then, overview related from perspectives performance analysis optimization, followed by widely used methodologies. Finally, open challenges future research direction context highlighted.