  A traditional cellular system (e.g., LTE) operates only on the licensed
spectrum. This tutorial explains the concept of cellular communications on both
licensed and license-exempt spectrum under a unified architecture. The purpose
to extend a cellular system into the bandwidth-rich license-exempt spectrum is
to form a larger cellular network for all spectrum types. This would result in
an ultimate mobile converged cellular network. This tutorial examines the
benefits of this concept, the technical challenges, and provides a conceptual
LTE-based design example that helps to show how a traditional cellular system
like the LTE can adapt itself to a different spectrum type, conform to the
regulatory requirements, and harmoniously co-exist with the incumbent systems
such as Wi-Fi. In order to cope with the interference and regulation rules on
license-exempt spectrum, a special medium access mechanism is introduced into
the existing LTE transmission frame structure to exploit the full benefits of
coordinated and managed cellular architecture.
