The first book to introduce user-centric ultra-dense network (UUDN) for 5G, including the concept, challenges, architecture and key technologies Proposes the novel principle of “de-cellular” and “user-centric” to meet the challenges faced by 5G in UDN scenario Presents the UUDN network architecture based on the novel principle Explores key characteristics of UUDN, including four aspects: Intelligent network knows user, Moving network follows user, Dynamic network serves user, Secured network protects user. Deciphers key technologies of UUDN, including: dynamic APs grouping (DAPGing) method, intelligent networking, advanced interference management, user-centric security Illustrates an experimental UUDN network with numerology and evaluation results Includes supplementary material: sn.pub/extras