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5G CommuniCations RaCe Pursuit of More Capacity Triggers LTE in Unlicensed Band anwer al-Dulaimi, Saba al-rubaye, Qiang ni, and Elvino Sousa ifth-generation (5G) network developers need to iden- noncoordinated and coordinated network managements to tify the necessary requirements toward additional enable coexistence between both technologies using trad- capacity and spectrally efficient wireless technolo- eoff performance for fair spectrum sharing. We concentrate gies. Therefore, the significant amount of underuti- on the initial coexistent technique and discuss how it maps F lized spectrum in the Wi-Fi band is motivating operators to to higher-layer improvements. This article shows new combine long-term evolution (LTE) with Wi-Fi technologies. approaches to achieve the Third-Generation Partnership This new LTE in unlicensed band (LTE-U) has the physical Project (3GPP) Release 13. layer topology to access Wi-Fi spectrum, specifically the 5-GHz band. Nevertheless, the evolution of LTE-U affects Introduction the Wi-Fi operations due to the absence of any regularity There is currently much interest in increasing the capa- for LTE-U transmissions in unlicensed band. In this article, bility of wireless networks to provide significantly high- we address the challenges for Wi-Fi to maintain transmis- er data rates to higher densities of users beyond the sions under the umbrella of LTE-U as Wi-Fi is pushed offline capability of current networks. To achieve such capaci- because of the listen-before-talk (LBT) feature. Therefore, ty increases, a