ABSTRACT
CONTENTS 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 5.2 Overview of Traditional LTE in the Licensed Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
5.2.1 Network Architectures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.2.1.1 LTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.2.1.2 IEEE LTE-Advanced . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
5.2.2 Overview of Physical Layer (PHY) Air Interfaces . . . . . . . . . . . . . . . . . . . . . . . . . 111 5.2.2.1 LTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 5.2.2.2 IEEE LTE-A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
5.2.3 Medium Access Control Scheduling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 5.2.3.1 LTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 5.2.3.2 LTE-A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.2.4 Traditional Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 5.2.4.1 LTE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 5.2.4.2 IEEE LTE-A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
5.3 Overview of Traditional Wi-Fi in the Unlicensed Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 5.3.1 Network Architectures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 5.3.2 Overview of Physical Layers (PHYs) of IEEE 802.11a/b/g/n/ac . . . . . . . . . . . . 116 5.3.3 Medium Access Control (MAC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
5.3.3.1 IEEE 802.11 Distributed Coordination Function (DCF) . . . . . . 117 5.3.3.2 IEEE 802.11e Enhanced Distributed Channel Access (EDCA) 118 5.3.3.3 IEEE 802.11n Reverse Direction Protocol (RDP) . . . . . . . . . . . . 120 5.3.3.4 IEEE 802.11ac Dynamic Channel Bandwidth Access (DCBA) 121 5.3.3.5 IEEE 802.11ad Directional MAC Access Protocols in the
Service Periods (SPs) and Contention-Based Periods (CBAPs) 121 5.3.4 Traditional Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
5.4 LTE in the Unlicensed Band . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 5.4.1 Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 5.4.2 Coexistence Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 5.4.3 Spectrum Regulations at the 5 GHz Unlicensed Band . . . . . . . . . . . . . . . . . . . . . . 129 5.4.4 LTE-U Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 5.4.5 Some Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
5.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
5.1 Introduction Cellular networks have evolved from the first generation (1G) systems to the current fourth generation (4G) systems with higher data rates in the downlink and the uplink from one generation to the next generation, leveraging on new technologies. Similarly, wireless local area networks or Wi-Fi have also evolved from one generation of standard to the next generation of standard. In terms of spectrum, cellular networks traditionally operate in the licensed band, while wireless local area networks traditionally operate in the unlicensed band. However, there is a trend to have (3.9)th generation (3.9G)/4G cellular networks operating in the unlicensed band to increase its throughput, while coexisting with wireless local area networks in recent years. Although Wi-Fi operates in the 2.4 GHz, 5 GHz and 60 GHz unlicensed band, the focus of having 3.9G/4G cellular networks in the unlicensed band is in the 5 GHz band initially. long-term evolution (LTE) is the 3.9 G cellular network, while LTE-Advanced is the 4G cellular network. The first name coined for such a scenario of cellular networks coexisting with Wi-Fi networks is LTE in the unlicensed band or LTE-U. Later, another name for this coexistence scenario in the unlicensed band is used-LTE licensed-assisted access (LAA).
