Wireless communication is a fast-growing field that attracts much research attention, from both industry and academia. As we progress to the next decade, the need for wireless connectivity will continue to grow, and the big challenge arises when the expected wireless system support new applications, such as metaverse, vehicle communication, and at space-air-ground domain. The demand-supply relationship in wireless communication will continue to push technologies forward. In this chapter, we briefly summarize active research for the next-generation wireless systems. 12.1 Joint Communication and Sensing Future wireless system not only desires for highly reliable and faster connectivity, but also the ability to sense surrounding dynamics with ubiquitous wireless signals [133]. Such sensing capabilities include range and velocity estimation, object detection, collision avoidance, and localization. In the past, communication and sensing have been designed separately, where either communication or sensing is the main target design, the other as the by-product. However, integrating both functionalities within one system has clear advantages in providing better power and spectral efficiency, as well as reducing hardware and signaling cost through efficient resource coordination [56, 117]. Joint communication and sensing has attracted extensive attention from the perspec- tive of jointly considering and unifying two operations, especially in emerging applications like vehicle-to-everything (V2X), where simultaneous information exchange and radar-like parameter estimation are critical. Yet, achieving integration gain from Joint communica- tion and sensing system faces numerous challenges. Among them, Joint communication and sensing physical layer design such as waveform optimization, collaborative resource allocation, and beamforming are of paramount importance. 12.2 Space-Air-Ground Communication One limitation for 5G wireless system is that it provides network access mainly for terres- trial (ground) communication. Emerg