Starting from the future application scenarios of mobile communications, this book analyzes the performance requirements and spectrum resources of 6G, combined with the network topology of wireless access networks, provides a comprehensive description of the basic functions of the wireless physical layer, including mobility management, wireless transmission, wireless positioning, and more. Building on the foundation of fourth and fifth-generation air interface technologies, it naturally transitions to 6G. The book delves into potential key technologies of 6G wireless networks in three major technical areas: coded multiple access waveform class, multi-antenna spatial domain class, and high-frequency deployment class. The content of the book is structured comprehensively, combining textual descriptions with mathematical formulas, emphasizing the impact of network topology, deployment frequency bands, and channel propagation characteristics on air interface design.