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Vol. 14. No. 03, 2023: 124-127
http://publikasi.mercubuana.ac.id/index.php/jte
p-ISSN: 20869479 e-ISSN: 2621-8534
Jurnal Teknologi Elektro, Vol. 14. No. 03, 2023
124
Improving SINR 4G/LTE Femtocell in the Coexisting
Network
Muhammad Yaser1*
Teknik Elektro, Universitas Pancasila, Jakarta
*muhammadyaser@univpancasila.ac.id
Abstract - The coexisting of LTE femtocell with existing GSM
network is proposed to address the challenge of limitation radio
frequency spectrum. SINR femtocells on coexisting networks are
strongly dependent on the state of femtocell distribution, including
the number and position of femtocells. On previous study have
been extensively discussed coexistence of LTE femtocell integrated
with GSM network. However, it has not been explicitly explained
how the approach for boosting SINR femtocell in this coexisting
network will be implemented. In this paper, several aspects
influencing SINR femtocell performance are mathematically
studied using computer simulation. Simulation results show that
SINR LTE femtocell increase about 0,2dB for every reduction of
one femtocell deployed on the GSM network. When m = 2, SINR
LTE femtocell reach 48.3dB then improve become 48.5dB when
m=1. Meanwhile, when position of femtocell away from GSM base
station from x = 0.1R to x = R, SINR LTE femtocell increase about
2.5dB for a single femtocell on each GSM network. So as to
increase SINR LTE femtocell can be done by reducing the number
of femtocells deployed on GSM network and set LTE femtocell
distribution patterns away from GSM base station.
Keyword—Coexisting, improving, LTE femtocell, SINR, network.
I. INTRODUCTION
Radio frequency spectrum is a limited natural resource that
has important value in telecommunications operations.
Spectrum management has an important role in planning radio
frequency spectrum usage as efficiently as possible to obtain
maximum benefit for all stakeholders, including service
providers and users [1]. Most countries set policies related to
radio frequency management, such as America, Norway, and
China have a framework of radio frequency management
[2],[3],[4]. In Indonesia radio frequency spectrum roadmap is
prepared every five years to meet the increasing demand of
mobile broadband [5].
To overcome spectrum limitation, the development of
technology demands a refarming of the frequency spectrum that
is very precious resource that can accommodate future
development and bring prosperity to the society. Refarming
itself is a term used for a spectrum reallocation process by
moving the operating frequency to produce contiguous
frequency bands. It provides sufficient bandwidth allocation for
a broadband system or more than one technology applied in a
particular frequency band simultaneously [6]. The benefit of
refarming to widen bandwidth has supported the deployment
plan of LTE from GSM frequencies and other mobile broadband
implementation plans [7], [8].
Spectrum refarming allows different generations of cellular
networks to use the same radio spectrum to improve the
spectrum utilization. Basically, spectrum sharing is
implemented in two ways i.e., overlay spectrum sharing, which
allows the secondary users opportunistically access the unused
spectrum of the primary users, and underlay spectrum sharing
which allows the secondary and primary users co-transmit at the
same band. Similarly, there are also two kinds of spectrum
refarming models i.e., overlay spectrum refarming model and
underlay spectrum refarming model.
Due to the rapid development of telecommunication
technology as shown in figure 1 [9], service provider has to find
the way to organize limited frequency resources, which of the
solution is finding incumbent operators called GSM refarming.
GSM refarming refers to phasing out currently used GSM
services and reallocating the frequency bands to more frequency
efficient and data optimized technologies such as 4G Long Term
evolution (LTE). The LTE system operate in GSM band belongs
to an overlay spectrum refarming model, where the Orthogonal
Frequency Division Multiple Access (OFDMA) utilizes the sub
bands that are not occupied by the GSM. However, the strong
need for GSM refarming. It is a time-consuming process as it is
complicated for mobile operator to shut down their GSM
network immediately due to the existing voice demand and
global roaming capability [10].
Figure 1 Evolution from 2G/3G/HSPA (+) to LTE [9]
Reviewing the problem and development related to the
allocation of radio frequency spectrum in Indonesia, a
comprehensive study is needed on the current conditions of
frequency spectrum allocation and the potential for refarming to
the future spectrum, for example 4G and beyond. Apart from
benefits of spectrum refarming, refarming is risky and exhibiting
a high potential of interference regarding migration between
fully occupied allocations. This challenge is influenced by
various factors, such as the number of service provider and their
initial operated spectrums. Problems are also emerging when
M. Yaser., Improving SINR 4G/LTE Femtocell in the Coexisting Network
Jurnal Teknologi Elektro, Vol. 14. No. 03, 2023
125
attempting to determine the allocated frequency and time of the
reallocation process to minimize disruptive services to users.
Therefore, a careful plan and step by step procedure in the
refarming execution is mandatory to make sure a success of
coexistence network.
The paper is organized as follow. In section II, we introduce
state of the art of this research. Section III gives system model
used in this study. Evaluation and result are presented in section
IV, this section also give discussion of the result. The conclusion
is outlined in section V.
II. LITERATURE REVIEW
In the coexisting network, LTE femtocells are deployed on
GSM macrocell network, a macrocell in a mobile phone
network provides radio coverage served by a high power
cellular base station. Usually, macrocells provide coverage
larger than any other technology i.e., microcells, femtocells,
relay nodes, picocells. This is because, the macrocell base
station are mounted on ground-based masts, rooftops and other
existing structures, at a height that provides a clear view over
the surrounding buildings. It also has a high-power output and
its performance can be increased by increasing the efficiency of
the transceiver. the locations of the macrocell base station are
carefully chosen through network planning, and the base station
settings are properly configured to maximize the coverage and
control the interference between them. As the traffic demand
grows and the radio frequency environment changes, the
network relies on cell splitting or additional carriers to
overcome limitation of capacity and transmission link.
However, this deployment process is complex and inefficient.
Furthermore, site acquisition for macrocell base station with
towers becomes more difficult in dense urban areas. Another
serious issue for macrocells is loss high penetration in indoor
environment, which has negative impact on the transmitted and
received signals. Therefore, LTE femtocells technology has
integrated into the GSM network in order to not only facilitate
transition GSM technology to LTE but also to improve user
broadband experience in a ubiquitous and cost-effective way.
These femtocells are recognized as the future of next generation
network as they are more affordable and cost effective than
other technologies.
Femtocell is an economical solution to provide reliable
high-speed indoor communications via using the existing
broadband Internet connection instead of the conventional
macrocell network. It is also known as home BS or home
evolved NodeB (Home eNB) which is operating in the licensed
spectrum that can integrate mobile and Internet technologies
within the home using optical fibre connection or DSL. From
the economics point of view, femtocell is a low-cost solution
compared to installing higher power macrocell to provide the
same quality of service for indoor coverage [11]
Based on this, the use of femtocell can benefit both the
service provider and the user. For a service provider, the
deployment of femtocells can improve the coverage, especially
indoors, capacity and reduce the consumption power. Coverage
is improved because femtocell can fill in the gaps and eliminate
loss of signal through buildings (i.e., penetration loss) [12].
Capacity on the other hand, is improved by reducing the number
of users attempting to use macrocell and by off-loading the
traffic through the user equipment network (via the internet) to
the operator's infrastructure [13]. Offloading the traffic from the
macro base station to the femtocell especially for indoor User
equipment who require higher transmission power and
resources, saves the base station resources and consumption
power. This will increase the network capacity, as the macrocell
will be able to serve more outdoor User while the femtocells
take care of the indoor user. Where, indoor User can benefit
from the improved indoor coverage by having indoor base
station i.e., in offices and homes to mitigate the negative impact
of the high penetration loss on their performance. As a result,
the user achieves the same or higher data rates using less power
as the transmission range between the femtocell and its user is
short and the battery life is long. Moreover, the authors in [12]
show that the user can achieve better voice quality and signal
strength via using the indoor femtocell for transmission rather
than being connected directly to the macro base station.
The coexisting of LTE femtocell with existing GSM
macrocell has been discussed in some studies. In [14] shows
that there are only limited opportunities to share frequencies on
the downlink network. In doing so, we are going to concern
about uplink transmit. In the coexisting network studied in [15],
LTE femtocell are deployed on GSM macrocell, yet, it operates
on GSM band under certain frequency allocation scheme as a
means of facilitating smooth transition to LTE on GSM
frequency band. Meanwhile, in [16,17] has been studied that
LTE femtocells are able to set off destructive interference to
LTE macro network when femtocell use constant frequency
channel with macrocell. Study about how to optimize
throughput in the coexisting network has been discussed in [18]
and impact macrocell size to the coexisting network
performance has been investigated in [19]. Before the
deployment LTE femto to GSM network, several questions
need to be investigated, including the extent to which the GSM
network and LTE femtocells deployed for each performance
will influence each other, then to what extent the system
performance changes due to changes in deployment conditions,
namely the impact of dynamic number of femtocells and
dynamic position of the femtocells deployment to SINR LTE
femtocell.
To resolve the inquiry, much work must be done. In
[11],[12],[13],[14],[15],[16] does not provide a clear and
comprehensive solution, so more metrics need to be defined and
compared in different scenarios. In view of that, we are going
to investigate various deployment conditions, for instance,
dynamic number of femtocells and dynamic deployment
position to improve SINR femtocell.
III. METHOD & SYSTEM MODEL
The coexisting network must be suitable for both GSM and
LTE systems. In the meaning that the deployment of LTE
femtocells does not reduce the performance of GSM networks,
besides, the coexisting will provide proper service in the newly
deployed LTE femtocell [20]
In the coexisting network, the LTE femtocells operate on
orthogonal frequency division multiplexing (OFDM)
M. Yaser., Improving SINR 4G/LTE Femtocell in the Coexisting Network
Jurnal Teknologi Elektro, Vol. 14. No. 03, 2023
126
technology so they are able to use several fractions of radio
frequency without interfering with other parts of the frequency
lying in between. LTE femtocell can use whole channels except
those are used by the GSM network where the femtocells are
located. The 4G/LTE system operate in GSM band belongs to
an overlay spectrum refarming mode
As we consider regularly located on GSM cells and assume
uniformly distributed GSM MSs and LTE femtocells, each reuse
cluster has the constant expected value of received interference.
Thus, we analyze the SINR of femtocell for a frequency channel
in the cluster f1 without loss of generality. The interference of the
LTE femtocell comes from GSM MSs that employ f1, femtocells
on other GSM cells Ψ(f1), and femtocells in the constant cell s
Figure 2. Interference LTE femtocell received in cell s
If Ijgl (x) be the expected value of interference from a GSM
MS in cell j provided that the distance between BS s and the
femtocell is x. As illustrated in Figure 2, the location of the GSM
MS relative to BS j is (rj ,θj), and that of the femtocell relative to
BS s is (x, βs). Then, by employing a polar coordinate where the
BS j is at (0, 0) and the BS k is at (Djs, 0), Ijgl (x) is provided as
follow:
Ijgl(x) =
(1)
Similarly, the average interference from a femtocell on
GSM cell k, which is denoted by Ikll(x), is provided as follow:
Ikll(x)=
(2)
The interference value from another femtocell in the
constant GSM cell s is denoted by Isll (x). In the polar coordinate
BS s is located at origin point, then Isll (x) is given in the
following.
Isll(x) =
(3)
Background noise at the femto BS and MS, Nbl = N0 Wg NFl
where NFl is the noise figure of LTE BS and MS. The expected
value SINR of the femtocell given M and x is as follow:
(4)
IV. EVALUATION AND RESULT
This study observed how dynamic femtocell number and
deployed position affect SINR LTE femtocell. Computer
simulation was used to provide a thorough understanding of the
relation between femtocell number change and deployment
position on SINR LTE femtocell. The parameters investigated
are listed in Table 1. GSM and LTE standard parameters were
employed in the studies.
Table 1 Parameters of SINR LTE femtocell
Parameter
Value
K
4
macrocell radius [km]
0.6km
femtocell position
(0.1R, 0.2R, R)
femtocell number
(1,2, 3...15)
Pg (R)
30 dB
Pl
eff
6 dB
No
-174 dB
Wg
200 kHz
5 dB
5 dB
Figure. 3 SINR LTE femtocell improve with dynamic
femtocell number and dynamic deployment position.
M. Yaser., Improving SINR 4G/LTE Femtocell in the Coexisting Network
Jurnal Teknologi Elektro, Vol. 14. No. 03, 2023
127
The result in figure. 3 shows when femtocells are deployed
near to the GSM base station, i.e., x = 0.1R, accommodating
one and more LTE femtocells per GSM network cause decrease
in SINR femtocell about 0.2dB, i.e., when M = 1, SINR LTE
femtocell reach 48.5dB then decrease become 48.3dB when
M=2, and the SINR LTE femtocell continue to decline due to
the increase of number deployed femtocell in each GSM
network. This trend occurs due to more femtocells number
accommodated on each GSM cell will be more inter- femtocell
interference, thus it decreases SINR LTE femtocell.
Meanwhile, SINR LTE femtocell increase as the farther
distance femtocell toward GSM base station (x). When change
from x = 0.1R to x = R, SINR LTE femtocell increase about
2.5dB for a single femtocell on each GSM network. The
strengthening of SINR LTE femtocell is caused by less inter-
femtocell interference because of farther distance. The farther
distance will increase path loss of interfering femtocell and
reduce inter-femtocell interference strength, hence it increases
the SINR LTE femtocell.
V. CONCLUSION
SINR LTE femtocell was highly dependent on number and
location of LTE femtocells deployed. On this study, SINR LTE
femtocell increased about 0,2dB for every reduction of one
femtocell deployed on the GSM network. Meanwhile when the
distance of femtocell away from GSM BS from x = 0.1R to
x = R, SINR LTE femtocell increased about 2.5dB for a single
femtocell on each GSM network. So as to improve SINR LTE
femtocell can be done by reducing the number of femtocells
deployed on GSM network and set LTE femtocell distribution
patterns away from GSM base station.
ACKNOWLEDGMENTS
We would like to thank all who helped us finish this research
and the editorial staff of the Journal of Electrical Technology
for publishing it.
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