This book provides a systematic introduction to the knowledge involved in the daily maintenance and optimization of 5G wireless networks, with a focus on the NR (New Radio) and signaling processes, as well as message content resolution. The book covers 5G theoretical foundation, network architecture, protocol stacks, NR channels, signaling process, etc. By reading this book, readers can quickly master the essential knowledge of 5G networks and have a thorough and clear understanding of 5G networks. The authors have written this book based on their own years of learning experience in mobile network optimization, centering around the needs of the optimization and maintenance personnel of the carriers. This book can be used as both a work guide for 5G optimization and maintenance personnel and a reference book for related practitioners to take the wireless network co-optation certification exam.