With the rapid deployment of 5G communication networks, the sixth-generation (6G) mobile network has attracted extensive attention from academia, industry, and government agencies, devoting to identifying critical drivers, performance requirements, and technological innovations.The progress of 6G networks in enhanced mobile broadband,massive machine-type communications and ultra-reliable and low-latency communications will promote the fast development of new services, e.g., Augmented Reality (AR), Virtual Reality (VR), holographic communications, Vehicle-to-Everything (V2X), self-driving cars, massive connections.Different services would have different features and requirements.In order to adapt to the ever-changing services, 6G should not only be intelligent and open to support full broadband services, but also enhance its capabilities compared with 5G.This will challenge 6G from various aspects, such as rate, delay, coverage, access, energy consumption, interaction, reliability, and degree of intelligence.