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T he evolving fifth generation (5G) cellular wireless networks
are envisioned to provide higher data rates,
enhance end-user quality-of-experience (QoE), reduce
end-to-end latency, and lower energy consumption. This
article presents several emerging technologies which could
enable and define future 5G mobile communication standards
and cellular networks. We highlight the key ideas for each
technology and the major open research challenges related to
measurement, testing and validating the performance of 5G
system components. Then, we highlight the fundamental research
challenges for resource management in 5G systems.
Introduction
The exponential growth of wireless data services driven by
mobile Internet and smart devices has triggered the investigation
of the 5G cellular network. Around 2020, the new 5G
mobile networks are expected to be deployed. 5G networks
will have to support multimedia applications with a wide variety
of requirements, including higher peak and user data rates,
reduced latency, enhanced indoor coverage, improved energy
efficiency, and so on.
The primary technologies and approaches to address
the requirements for 5G systems can be classified as follows
[1]–[3]:
◗ densification of existing cellular networks with the
massive addition of small cells and a provision for peerto-peer
(P2P) communication (e.g., device-to-device
(D2D) and machine-to-machine (M2M) communicationenabled
multi-tier heterogeneous networks);
◗ simultaneous transmission and reception (e.g., fullduplex
(FD) communication);
◗ massive multiple-input multiple-output (massiveMIMO)
and millimeter-wave (mm-wave communications
technologies;
◗ improved energy efficiency by energy-aware communication
and energy harvesting;
◗ cloud-based radio access network (C-RAN); and
◗ virtualization of wireless resources.
The visions and requirements of 5G networks and the corresponding
technologies are in Table 1.
Networks and Devices for 5G Systems
The 5G networks will consist of nodes/cells with heterogeneous
characteristics and capacities (such as macrocells, small
cells (e.g., femtocells and picocells), D2D user equipment
(UE), etc.), which will result in a multi-tier architecture. Due
to increasing complexity in network management and coordination
among multiple network tiers, the network nodes will
have the capability of self-organization (e.g., autonomous load
balancing, interference minimization, spectrum allocation,
power adaptation, etc.) [2]. Also, a UE will have simultaneous
active connections to more than one base station (BS) or access
point (AP) using the same or different radio access technologies
(RATs). The heterogeneous nodes (e.g., UE, BSs, smart
machines, wearable devices, etc.) will be integrated through
a unified (possibly cloud-based) network to provide seamless
connectivity. The communication efficiency in 5G systems will
be improved by incorporating techniques such as coordinated
multipoint (CoMP) joint transmission and reception, networkassisted
interference cancellation and suppression, spectrum
reuse (e.g., non-orthogonal multiple access), and three-dimensional
or full-dimensional MIMO [4]. In addition, the use
of a large number of remote radio heads (RRHs) connected to
central processing nodes (e.g., clouds) with the high-speed
backhaul/fronthaul is also envisioned [3].
Due to the emerging trends of energy-aware FD communication
and spectrum virtualization, 5G device architectures will
be more complex than those with 4G systems. Devices in the 5G
networks should be capable of operating in multiple spectrum
bands, ranging from radio frequency (RF) to mm-wave, while
being backward compatible (e.g., with existing technologies
such as 3G and 4G). Due to energy hungry multimedia applications,
energy efficiency will be an important feature for 5G user
experience, and hence, it is desirable that the devices integrate
energy harvesting technologies [3]. With the need to support
several RATs, FD communication and energy harvesting