IEEE Communications Magazine - June 2017 - page 81

79
IEEE Communications Magazine • June 2017
0163-6804/17/$25.00 © 2017 IEEE
A
bstract
The next generation of wireless telecommuni-
cations, 5G, is expected to have tight interworking
between its novel air interface and legacy stan-
dards, such as the LTE. The major difference from
interworking between previous RAT generations
is that there will be common CN functionalities,
enabling faster RAT scheduling due to reduced
time spent with signaling. In this context, this arti-
cle aims at exploiting an FS solution to improve
QoS metrics of the system by means of efficient
RAT scheduling. Analyses presented here show
a better understanding concerning which system
measurements are most efficient in a mutliple-RAT
scenario. More specifically, we present an analysis
concerning the metrics that should be used as
RAT scheduling criteria and how frequent these
switching evaluations should be done. Finally,
we also compare the performance of DC and FS
solutions, highlighting the scenarios in which each
of them performs better than the other.
I
ntroduction
The history of wireless telecommunication systems
shows that during the launch of a new generation,
the new technology coexists with legacy ones
even if they are independent, for example, wide-
band code-division multiple access (WCDMA)
and Long Term Evolution (LTE). Since new gener-
ations usually have different capabilities and oper-
ate in different frequency bands, the need for an
abrupt upgrade of all radio equipment could be
expected. However, this coexistence, that is, the
equipments of different networks are collocated
without interaction between them or significantly
impact their performance, allows providers and
users a gradual transition from one technology to
another.
Regarding the next generation, ongoing fifth
generation (5G) research projects, such as [1],
are considering tight interworking, that is, ter-
minals of one network may communicate with
equipment of another, instead of only coexis-
tence, between a novel 5G radio access technol-
ogy (RAT), called New Radio (NR), and legacy
standards such as LTE. This integration is here
called the 5G multi-RAT scenario. This is due
to the fact that 5G is expected to operate in a
wide range of frequencies, including very high
millimeter-wave (mmWave) bands [2]. In the high
frequency part of the spectrum, the propagation
conditions are challenging: lower diffraction, high-
er path loss, and so on. Beamforming and massive
multiple-input multiple-output (MIMO) antennas
are two of the proposed concepts to overcome
this issue. However, since they require high levels
of directivity, one of the bottlenecks associated
with them is the difficulty in keeping track of the
channel variations in time due to user mobility [3].
Thus, among other advantages, the interworking
between 5G and legacy technologies will increase
the system reliability, considering that legacy tech-
nologies can act as a backup link.
This tight interworking between NR and LTE is
illustrated in Fig. 1. It highlights three of the pos-
sible connectivity solutions that will be present in
this scenario, which are: single connection (the
UE is served only by one RAT); dual connectivity
(DC) (the user equipment, UE, is served by LTE
and NR at the same time); and fast-RAT schedul-
ing (FS) (the UE quickly switches from one RAT
to another, since there is a backhaul link between
the RATs).
This article investigates how to improve quali-
ty of service (QoS) metrics by means of efficient
RAT scheduling. More specifically, we focus on
the measurement system to monitor the chan-
nel propagation conditions of different base sta-
tions (BSs) in order to switch as fast as possible
to the one that fits better. To this end, we present
an analysis concerning the metrics that should
be used as a RAT scheduling criterion and how
frequent these scheduling evaluations should be
done.
Before addressing this problem, we present in
more detail the considered connectivity solutions
in the next section.
B
ackground on
C
onnectivity
S
olutions
H
ard
H
andover
Previous cellular technologies (e.g., WCDMA
and LTE) use so-called inter-RATs hard handover
(HH) to hand over a connection from one RAT to
another. To enable this, the UEs need to be able
to measure some sort of signal strength on the
target RAT. Typically, an inter-RAT handover only
occurs if the signal from the current RAT is below
a threshold and the target RAT is above anoth-
er threshold. In this case, the current BS sends a
request to the target RAT via the core networks
(CNs) of the two radio networks. The target RAT
then generates a handover command and sends
this to the source RAT (i.e., the source RAT’s BS).
The source BS then conveys this message to the
UE. This handover message contains the neces-
Fast-RAT Scheduling in a
5G Multi-RAT Scenario
Victor Farias Monteiro, Mårten Ericson, and Francisco Rodrigo P. Cavalcanti
A
gile
R
adio
R
esource
M
anagement
T
echniques
for
5G N
ew
R
adio
The authors exploit an FS
solution to improve QoS
metrics of the system by
means of efficient RAT
scheduling. Analyses
presented here show
a better understanding
concerning which system
measurements are most
efficient in a mutliple-RAT
scenario. More specifical-
ly, they present an analy-
sis concerning the metrics
that should be used as
RAT scheduling criteria
and how frequent these
switching evaluations
should be done.
Victor Farias Monteiro and Francisco Rodrigo P. Cavalcanti are with the Wireless Telecommunications Research Group, Federal University of Ceará;
Mårten Ericson is with Ericsson Research.
Digital Object Identifier:
10.1109/MCOM.2017.1601094
1...,71,72,73,74,75,76,77,78,79,80 82,83,84,85,86,87,88,89,90,91,...228
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