This book systematically introduces the new technologies and characteristics emerging in 5G communication systems. Different from traditional communication systems that focus on analog and digital analysis methods, design principles, and hardware implementations, this book emphasizes key technologies in the new era such as cloud computing, spatial-temporal wireless channels, and multi-carrier modulation. It is suitable for undergraduate students majoring in electronic information, computer science, and automatic control, and can also serve as a teaching reference for lower-level graduate students.