Published online by Cambridge University Press: 28 April 2017
Introduction
In recent years, wireless service providers in different countries have deployed both the Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) and LTE-Advanced systems. Despite the unprecedented data rates and quality of service (QoS) provided by these new networks, user demand is beginning to exceed their capabilities. For example, the proliferation of smartphones and tablets has caused a significant and sustained increase in mobile data traffic. In fact, in 2015 alone, global mobile data traffic grew by 74% from 2.1 to 3.7 exabytes [1]. Furthermore, the existing networks are not well suited for the exceedingly large number of devices and appliances that are expected to be connected wirelessly to the Internet in future Internet of Things (IoT) applications and machine-to-machine (M2M) communications. Moreover, to make the growth of networks and the number of connected devices economically and ecologically sustainable, energy efficiency has to be substantially improved. Also, emerging new applications such as remote surgery in healthcare, autonomous driving, and wireless control of industrial robots require ultra-low latencies in the sub-millisecond range and ultra-high reliability, giving rise to the notion of the Tactile Internet. In order to support the exponential growth of existing mobile traffic and the emergence of new wireless applications and services, researchers and standardization bodies worldwide have set out to develop a fifth generation (5G) of wireless networks [2–6]. Some of the stringent requirements for this next generation of wireless networks are listed in Table 1.1 [7].
To meet these challenging requirements, a mere evolution of the current networks is not sufficient. Instead, a true revolution of technologies in both the radio access network and the mobile core network is needed (Figure 1.1). In the radio access network, fundamentally new physical layer technologies such as massive multiple-input multiple-output (MIMO), non-orthogonal multiple access (NOMA), full-duplex (FD) communication, millimeter wave (mmWave) communication, device-to-device (D2D) communication, and visible light communication (VLC) will be deployed. Furthermore, leveraging cloud computing, the cloud radio access network (C-RAN) has emerged as a promising and cost-efficient mobile network architecture to enhance the spectrum and energy efficiency of 5G networks. In addition, different access technologies, including LTE and Wireless Fidelity (Wi-Fi), may be integrated to guarantee seamless coverage, and to support high data-rate transmission and data offloading.
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