![](https://csdnimg.cn/release/download_crawler_static/86532959/bg2.jpg)
IEEE Communications Magazine • February 2014
123
people crave faster Internet access on the move,
trendier mobiles, and, in general, instant com-
munication with others or access to information.
More powerful smartphones and laptops are
becoming more popular nowadays, demanding
advanced multimedia capabilities. This has
resulted in an explosion of wireless mobile
devices and services. The EMO pointed out that
there has been a 92 percent growth in mobile
broadband per year since 2006 [2]. It has been
predicted by the Wireless World Research
Forum (WWRF) that 7 trillion wireless devices
will serve 7 billion people by 2017; that is, the
number of network-connected wireless devices
will reach 1000 times the world’s population [4].
As more and more devices go wireless, many
research challenges need to be addressed.
One of the most crucial challenges is the
physical scarcity of radio frequency (RF) spectra
allocated for cellular communications. Cellular
frequencies use ultra-high-frequency bands for
cellular phones, normally ranging from several
hundred megahertz to several gigahertz. These
frequency spectra have been used heavily, mak-
ing it difficult for operators to acquire more.
Another challenge is that the deployment of
advanced wireless technologies comes at the cost
of high energy consumption. The increase of
energy consumption in wireless communication
systems causes an increase of CO
2
emission indi-
rectly, which currently is considered as a major
threat for the environment. Moreover, it has
been reported by cellular operators that the
energy consumption of base stations (BSs) con-
tributes to over 70 percent of their electricity bill
[5]. In fact, energy-efficient communication was
not one of the initial requirements in 4G wire-
less systems, but it came up as an issue at a later
stage. Other challenges are, for example, aver-
age spectral efficiency, high data rate and high
mobility, seamless coverage, diverse quality of
service (QoS) requirements, and fragmented
user experience (incompatibility of different
wireless devices/interfaces and heterogeneous
networks), to mention only a few.
All the above issues are putting more pres-
sure on cellular service providers, who are facing
continuously increasing demand for higher data
rates, larger network capacity, higher spectral
efficiency, higher energy efficiency, and higher
mobility required by new wireless applications.
On the other hand, 4G networks have just about
reached the theoretical limit on the data rate
with current technologies and therefore are not
sufficient to accommodate the above challenges.
In this sense, we need groundbreaking wireless
technologies to solve the above problems caused
by trillions of wireless devices, and researchers
have already started to investigate beyond 4G
(B4G) or 5G wireless techniques. The project
UK-China Science Bridges: (B)4G Wireless Mobile
Communications (http://www.ukchinab4g. ac.uk/) is
perhaps one of the first projects in the world to
start B4G research, where some potential B4G
technologies were identified. Europe and China
have also initiated some 5G projects, such as
METIS 2020 (https://www.metis2020. com/) sup-
ported by EU and National 863 Key Project in
5G supported by the Ministry of Science and
Technology (MOST) in China. Nokia Siemens
Networks described how the underlying radio
access technologies can be developed further to
support up to 1000 times higher traffic volumes
compared to 2010 travel levels over the next 10
years [6]. Samsung demonstrated a wireless sys-
tem using millimeter (mm) wave technologies
with data rates faster than 1 Gb/s over 2 km [7].
What will the 5G network, which is expected
to be standardized around 2020, look like? It is
now too early to define this with any certainty.
However, it is widely agreed that compared to
the 4G network, the 5G network should achieve
1000 times the system capacity, 10 times the
spectral efficiency, energy efficiency and data
rate (i.e., peak data rate of 10 Gb/s for low
mobility and peak data rate of 1 Gb/s for high
mobility), and 25 times the average cell through-
put. The aim is to connect the entire world, and
achieve seamless and ubiquitous communica-
tions between anybody (people to people), any-
thing (people to machine, machine to machine),
wherever they are (anywhere), whenever they
need (anytime), by whatever electronic
devices/services/networks they wish (anyhow).
This means that 5G networks should be able to
support communications for some special sce-
narios not supported by 4G networks (e.g., for
high-speed train users). High-speed trains can
easily reach 350 up to 500 km/h, while 4G net-
works can only support communication scenarios
up to 250 km/h. In this article, we propose a
potential 5G cellular architecture and discuss
some promising technologies that can be
deployed to deliver the 5G requirements.
The remainder of this article is organized as
follows. We propose a potential 5G cellular
architecture. We describe some promising key
technologies that can be adopted in the 5G sys-
tem. Future challenges are highlighted. Finally,
conclusions are drawn.
A POTENTIAL 5G WIRELESS
CELLULAR ARCHITECTURE
To address the above challenges and meet the
5G system requirements, we need a dramatic
change in the design of cellular architecture. We
know that wireless users stay indoors for about
80 percent of time, while only stay ourdoors
about 20 percent of the time [8]. The current
conventional cellular architecture normally uses
an outdoor BS in the middle of a cell communi-
cating with mobile users, no matter whether they
stay indoors or outdoors. For indoor users com-
municating with the outdoor BS, the signals have
to go through building walls, and this causes very
high penetration loss, which significantly dam-
ages the data rate, spectral efficiency, and ener-
gy efficiency of wireless transmissions.
One of the key ideas of designing the 5G cel-
lular architecture is to separate outdoor and
indoor scenarios so that penetration loss through
building walls can somehow be avoided. This will
be assisted by distributed antenna system (DAS)
and massive MIMO technology [9], where geo-
graphically distributed antenna arrays with tens
or hundreds of antenna elements are deployed.
While most current MIMO systems utilize two
to four antennas, the goal of massive MIMO sys-
One of the key ideas
of designing the 5G
cellular architecture is
to separate outdoor
and indoor scenarios
so that penetration
loss through building
walls can be some-
how avoided. This
will be assisted by
distributed antenna
system (DAS) and
massive MIMO
technology.
WANG_LAYOUT.qxp_Layout 1/30/14 1:29 PM Page 123