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LTE in the Unlicensed Spectrum: A Survey

ABSTRACT Fueled by the increasing popularity of handheld mobile devices with powerful data processing capabilities, the wireless industry is witnessing an avalanche of mobile traffic. This unprecedented escalation has imposed significant challenges due to the limited licensed spectrum for cellular networks. Any effort to achieve capacity growth through network densification will face the challenge of severe inter-cell interference. Among the most effective solutions to this issue is to make the best use of all spectrum types through matured technology. Long-term evolution (LTE) access to unlicensed spectrum is considered one of the latest groundbreaking innovations to provide high-performance and a seamless user experience under a unified radio technology by extending LTE to the readily available unlicensed spectrum. In this article, we introduce the dawn of LTE access to unlicensed spectrum as a boon to the spectrum scarcity problem. Then, we explore deployment scenarios for LTE in unlicensed spectrum. We further identify key issues in bringing LTE unlicensed spectrum access to reality, together with other technologies for accessing unlicensed spectrum, specifically Wi-Fi. Finally, we discuss some existing coexistence mechanisms for successful, harmonious deployment of LTE and Wi-Fi in the same unlicensed band.