IEEE Communications Magazine - June 2017 - page 88

IEEE Communications Magazine • June 2017
0163-6804/17/$25.00 © 2017 IEEE
Millimeter-wave frequencies between 6 and
100 GHz provide orders of magnitude larger
spectrum than current cellular allocations and
allow usage of large numbers of antennas for
exploiting beamforming and spatial multiplexing
gains. In this article, we describe the main design
concepts when integrating mmWave RANs into
5G systems, considering aspects such as spec-
trum, architecture, and backhauling/fronthauling.
The corresponding RRM challenges, extended
RRM functionalities for 5G mmWave RAN, and
RRM splits are addressed. Finally, based on these
discussions, a framework is proposed that allows
joint backhaul and access operation for 5G
mmWave RAN, which we envisage as one of the
key innovative technologies in 5G. The proposed
framework consists of a joint scheduling and
resource allocation algorithm to improve resource
utilization efficiency with low computational com-
plexity and to fully exploit spatial multiplexing gain
for fulfilling user demands.
The success of cellular communication tech-
nologies has resulted in the explosive demand
of mobile data traffic, which is expected to have
an eight-fold growth within five years [1]. Corre-
spondingly, fifth generation (5G) cellular networks
aim to deliver as much as 1000 times the capacity
relative to current levels [2]. To fulfill such require-
ments, cell densification, more bandwidth, and
higher spectral efficiency are required.
Considering the spectrum shortage situation
in the favorite 300 MHz to 3 GHz frequencies
used by most of today’s wireless communication
systems and limited potential for spectral efficien-
cy enhancement, utilization of a large amount of
bandwidth in millimeter wave (mmWave) bands
seems to be indispensable [3]. The available band-
widths in these bands, for example, in Ka-band
(26.5–40 GHz), V-band (57–71 GHz), and E-band
(71–76 GHz and 81–86 GHz), can significantly
exceed all allocations in contemporary cellular
networks. Moreover, the very small wavelengths
of mmWave signals combined with advanced
low-power complementary metal oxide semicon-
ductor (CMOS) RF circuits enable deploying large
numbers of miniaturized antennas and exploita-
tion of beamforming and spatial multiplexing gain
However, mmWave signals suffer from
increase in isotropic free space loss, higher pen-
etration loss, and propagation attenuation due
to atmosphere absorption by oxygen molecules,
water vapor, and rain drops [5], resulting in out-
ages and intermittent channel quality. Therefore,
higher antenna gain is required at both transceiv-
er sides, where directional transmissions have
impact on radio resource usage, multiple access,
and interference characteristics, and correspond-
ingly affect radio access networks (RANs) and
radio resource management (RRM) design. Fur-
thermore, heterogeneous networks (HetNets),
with small cells densely deployed underlying con-
ventional homogeneous macrocells, have been
treated as one promising candidate of mmWave
RAN architecture to cope with the adverse
propagation conditions [6]. In particular, close
interworking between small cells and macrocells
enables users to have simultaneous connection
to both macrocell base stations (BSs) and small
cell access points (APs), thus improving coverage
and augmenting overall capacity. The challenge
of having large numbers of small cells lies in the
expense or practicality of equipping every cell
with fiber connectivity. As an attractive cost-effi-
cient alternative, wireless backhauling provides
technology- and topology-dependent coverage
extension and capacity expansion to fully exploit
the heterogeneity of the networks. A further step
in this paradigm is wireless self-backhauling, which
uses the same frequency band for both backhaul
(BH) and access links, leading to challenges in
RRM between BH and access links. Thus, joint BH
and access RRM is desired for 5G mmWave RAN
to optimize system efficiency.
The rest of the article is organized as fol-
lows. We start with explaining the fundamental
principles of mmWave RAN design in 5G, and
discussing spectrum and architecture options,
backhauling aspects, and the new notion of
resource. We continue with providing details
regarding the RRM challenges in the mmWave
RAN. Finally, we elaborate our illustrative appli-
cation scenario of interest, that is, joint BH and
access operation, and address the corresponding
Radio Resource Management
Considerations for 5G Millimeter Wave
Backhaul and Access Networks
Yilin Li, Emmanouil Pateromichelakis, Nikola Vucic, Jian Luo, Wen Xu, and Giuseppe Caire
5G N
The authors describe
the main design con-
cepts when integrating
mmWave RANs into 5G
systems, considering
aspects such as spec-
trum, architecture, and
The corresponding RRM
challenges, extended
RRM functionalities for 5G
mmWave RAN, and RRM
splits are addressed.
Yilin Li, Emmanouil Pateromichelakis, Nikola Vucic, Jian Luo, and Wen Xu are with Huawei Technologies Düsseldorf GmbH;
Giuseppe Caire is with Technische Universität Berlin.
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