  The fifth generation (5G) of wireless communication is in its infancy, and
its evolving versions will be launched over the coming years. However,
according to exposing the inherent constraints of 5G and the emerging
applications and services with stringent requirements e.g. latency, energy/bit,
traffic capacity, peak data rate, and reliability, telecom researchers are
turning their attention to conceptualize the next generation of wireless
communications, i.e. 6G. In this paper, we investigate 6G challenges,
requirements, and trends. Furthermore, we discuss how artificial intelligence
(AI) techniques can contribute to 6G. Based on the requirements and solutions,
we identify some new fascinating services and use-cases of 6G, which can not be
supported by 5G appropriately. Moreover, we explain some research directions
that lead to the successful conceptualization and implementation of 6G.
