Cellular communications on license-exempt spectrum

Abstract

A traditional cellular system (e.g., LTE) operates only on licensed spectrum. This article describes the concept of cellular communications on both licensed and license-exempt/unlicensed spectrum under a unified architecture. The purpose of extending a cellular system into the bandwidth-rich license-exempt spectrum is to form a larger cellular network for both spectrum types. This would result in an ultimate mobile converged cellular network. This article examines the benefits of this concept and the technical challenges, and provides a conceptual LTE-based design example that demonstrates how a traditional cellular system like LTE can adapt itself to a different spectrum type, conform to the regulatory requirements, and harmoniously coexist with the incumbent systems such as WiFi. In order to cope with the interference and regulatory 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.