  The Internet of Things (IoT) is the enabler for smart city to achieve the
envision of the "Internet of Everything" by intelligently connecting devices
without human interventions. The explosive growth of IoT devices makes the
amount of business data generated by machine-type communications (MTC) account
for a great proportion in all communication services. The fifth-generation (5G)
specification for cellular networks defines two types of application scenarios
for MTC: One is massive machine type communications (mMTC) requiring massive
connections, while the other is ultra-reliable low latency communications
(URLLC) requiring high reliability and low latency communications. 6G, as the
next generation beyond 5G, will have even stronger scales of mMTC and URLLC.
mMTC and URLLC will co-exist in MTC networks for 5G 6G-enabled smart city. To
enable massive and reliable LLC access to such heterogeneous MTC networks where
mMTC and URLLC co-exist, in this article, we introduce the network architecture
of heterogeneous MTC networks, and propose an intelligent hybrid random access
scheme for 5G/6G-enabled smart city. Numerical results show that, compared to
the benchmark schemes, the proposed scheme significantly improves the
successful access probability, and satisfies the diverse quality of services
requirements of URLLC and mMTC devices.
