Energy-efficient user association mechanism enabling fully hybrid spectrum sharing among multiple 5G cellular operators

TELKOMNIKA, Vol.17, No.6, December 2019, pp.3203~3210
ISSN: 1693-6930, accredited First Grade by Kemenristekdikti, Decree No: 21/E/KPT/2018
DOI: 10.12928/TELKOMNIKA.v17i6.13058 ◼ 3203
Received May 7, 2019; Revised June 10, 2019; Accepted July 2, 2019
Energy-efficient user association mechanism
enabling fully hybrid spectrum sharing
among multiple 5G cellular operators
Mothana L. Attiah*1
, A. A. Md Isa2
, Zahriladha Zakaria3
, Ahmed M. Dinar4
,
M. K. Abdulhameed5
, Mowafak K. Mohsen6
1–6
Centre for Telecommunication Research and Innovation (CeTRI), Faculty of Electronic and Computer
Engineering (FKeKK), Universiti Teknikal Malaysia Melaka (UTeM), Malaysia
1
Department of Computer Engineering, Electrical Engineering Technical College,
Middle Technical University, Baghdad, Iraq
*Corresponding author, e-mail: mothana.utem@gmail.com
Abstract
Spectrum sharing (SS) is a promising solution to enhance spectrum utilization in future cellular
systems. Reducing the energy consumption in cellular networks has recently earned tremendous attention
from diverse stakeholders (i.e., vendors, mobile network operators (MNOs), and government) to decrease
the CO2 emissions and thus introducing an environment-friendly wireless communication. Therefore,
in this paper, joint energy-efficient user association (UA) mechanism and fully hybrid spectrum sharing
(EE-FHSS) approach is proposed considering the quality of experience QoE (i.e., data rate) as the main
constraint. In this approach, the spectrum available in the high and low frequencies (28 and 73 GHz) is
sliced into three portions (licensed, semi-shared, and fully-shared) aims to serve the users (UEs)
that belong to four operators in an integrated and hybrid manner. The performance of the proposed
QoE-Based EE UA-FHSS is compared with the well-known maximum signal-to-interference-plus-noise
ratio (max-SINR UA-FHSS). Numerical results show that remarkable enhancement in terms of EE for
the four participating operators can be achieved while maintaining a high degree of QoE to the UEs.
Keywords: energy efficiency, green 5G communication, hybrid spectrum sharing (HSS)
Copyright © 2019 Universitas Ahmad Dahlan. All rights reserved.
1. Introduction
The envisioned enormous growth in the diverse innovative technologies and services
in future cellular communication era (i.e., Internet of Things (IoT), autonomous driving,
augmented reality, and virtual reality) are resulting in increased demand for higher spectral and
energy efficiency to meet such bandwidth and energy-hungry applications [1, 2]. Given
the excellent opportunities of mmWave frequencies such as the huge amount of spectrum as
well as the super interference-reduction merits [3], achieving success in relying on such
technology became very possible [4]. Despite such a wide spectrum range, it is still not
unlimited if other services that utilize the same bands are considered [5]. Nevertheless, due to
the limited coverage range of mmWave communications [6], adding more minicell towers
or relays throughout the hot spot area is essential to achieve better QoS. This may exacerbate
the problem of energy consumption as more mmWave base stations (mBSs) are deployed.
In particular, BSs are considered the main source of energy consumption in cellular
networks, accounting for 57% of total energy requirements [7]. Spectrum sharing approach
(SSA) can be a possible solution in the 5th generation (5G) mobile networks to overcome
the above-mentioned issues [8]. Such an approach allows multiple users (UEs) to share
the same resources in the power domain [9] which in turn supports massive connectivity using
the same time-frequency resource with an acceptable mBSs density. Therefore, it is imperative
to assess the system performance considering SSA from the energy consumption perspective
as it considered as a fundamental design objective for the next generation cellular
networks [10]. Through the literature, plenty of efforts have been conducted seeking for
an environment-friendly wireless communication that involves a single-radio access technology
(S-RATs). However, it is expected that 5G will support multi-RATs to provide ultra-reliable
communication [11]. Consequently, many scholars are shifted from assessing the energy

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TELKOMNIKA Vol. 17, No. 6, December 2019: 3203-3210
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efficiency (EE) of the cellular systems that support S-RATs to those with multi-RATs
capabilities, especially with the presence of resource sharing approach. For instance, joint
spectrum and energy efficient mmWave transmission scheme was presented in [12] that
combines the notion of non-orthogonal multiple access (NOMA) with beam space multiple-input
multiple output (MIMO). Power control and allocation are targeted by many researches
to improve EE by means of utilising different transmission power value in an adaptive way.
The idea of jointly optimising cell-association and power-control was proposed in [13] taking
the fast vehicle mobility and the traffic load conditions into consideration. In [14], a new adaptive
spectrum sharing schemes account for the channel estimation errors to improve EE considering
both half-duplex (HD) and full-duplex (FD) transmission. However, this scheme gave the priority
to the primary users (PUs).
Most of the existing works on multi-independent 5G mmWave cellular operators have
focused on coverage and rate probability optmisation [3, 5, 15–21]. There are limited works
on energy-efficient UA that support spectrum sharing among multiple cellular operators, which
is more complicated owing to the multi-carrier and multi-independent-RAT nature. Therefore,
in this paper, energy efficient UA mechanism enabling FHSS approach underlying
multi-independent 5G mmWave cellular operators is proposed while satisfying the QoE
(i.e., rate provisioning) constraints to the UEs to gain more insights about the possibility of jointly
maximising energy efficiency for all the participating operators taking into account maintaining
an acceptable level of 5G constraints.
2. Research Method
In this section, we first elaborate on the network model, followed by a set of
mathematical models related to the transmission model. Finally, some detailed description of
the proposed EE-FHSS approach is presented.
2.1. Network Model
Two tiers of multi-independent 5G mmWave cellular operators given by 𝒩.
Four operators are considered in this work underlying spectrum sharing approach in which each
operator 𝒩 𝑡ℎ
constituted of a set of mmWave base stations (mBSs) distinguished by 𝒦 𝒩
𝑡ℎ
.
Each 𝒦 𝒩
𝑡ℎ
operates optionally at both carrier frequencies (28 and 73 GHz) depends on the value
of 𝒞 𝓂 ∈ {0,1} such that if 𝒞 𝓂=0 then the carrier is 28 GHz and if 𝒞 𝓂=1 then the carrier is
73 GHz. More precisely, each 𝒦 𝒩
𝑡ℎ
operates in a particular mode (licensed, semi-pooled,
fully-pooled) based on the index 𝓂. Let 𝒲 𝒩,𝒞 stands for the allocated spectrum to each
operator 𝒩 𝑡ℎ
. Let 𝒦 𝒩 be a set of mBSs belong to operator 𝒩 𝑡ℎ
and 𝒦 = 𝒦1 ∪ 𝒦1 … ∪ 𝒦𝑡ℎ refers
to a set of all mmWave base stations in the proposed architecture. Motivated by 5G small cells
can be easily attached to the street light poles, all mBSs are densely deployed following
grid-based layout in a hot spot area ℝ2. Let 𝒰 denotes a set of outdoor user equipments
(UEs) and 𝒰 = 𝒰1 ∪ 𝒰1 … ∪ 𝒰 𝒩, where, 𝒰 𝒩 represents a set of UEs that subscribes to
an operator 𝒩 𝑡ℎ
. 𝒦 𝒩 can serve 𝒰(𝑡ℎ,𝒩)
which are subscribing to its own or to different
operator via licensed, semi-shared or fully-shared spectrum access strategy and the quality of
the link between the 𝒰(𝑡ℎ,𝒩)
and the tagged 𝒦 𝒩
𝑡ℎ
. Furthermore, all UEs are equipped with
multi-antenna systems.
2.2. Transmission Model
In this work, the log-normal shadowing path-loss model given by (1) is utilized to
compute the received signal power at the receiving side (RX) with path-loss exponent γ and
wavelength (3.4, 3.3 dB and 10.71, 4.106 mm) for both 28 GHz and 73 GHz carrier frequency
respectively [22]:
𝑃𝐿𝑑 𝒰𝒦
(𝒩,𝒞)
= 𝑃𝐿𝑓𝑠(𝑑 𝑜) + 10 × 𝛾 × 𝑙𝑜𝑔10 (
𝑑 𝒰𝒦
𝑑 𝑜
) + 𝑥 𝜎, (1)
where 𝑃𝐿𝑑 𝒰𝒦
(𝒩,𝒞)
, 𝑑 𝒰𝒦, 𝑃𝐿 𝑓𝑠(𝑑 𝑜) stand for the path loss in dB for a typical UE
𝒰(𝑡ℎ,𝒩)
associated with mBS 𝒦 𝒩
𝑡ℎ
utilising carrier frequency 𝒞 and owned by operator 𝒩 𝑡ℎ
,
the separation distance in meters, and the close-interference free space path loss in dB

TELKOMNIKA ISSN: 1693-6930 ◼
Energy-efficient user association mechanism enabling fully hybrid... (Mothana L. Attiah)
3205
as identified in (2) respectively. Considering the close-in free space reference distance 𝑑 𝑜
is equal to 1 meter; 𝑥 𝜎 denotes zero-mean Gaussian random variable with 𝜎 as a standard
deviation in (dB).
𝑃𝐿𝑓𝑠(𝑑 𝑜) = 20 × 𝑙𝑜𝑔10 (
4×𝜋×𝑑 𝑜
𝜆
), (2)
Typically, one of the most important factors in the calculation of the average received
signal power at the receiver side is the path loss attenuation. Therefore, we first apply (1)
to calculate the path loss attenuation and then execute (3) as follows:
Pr 𝒰𝒦
(𝒩,𝒞)
= Pt
(𝒩,𝒞)
+ 𝐺𝑡
(𝒩,𝒞)
+ 𝐺𝑟
(𝒩,𝒞)
− 𝑃𝐿 𝒰𝒦
(𝒩,𝒞)
(3)
where Pt
(𝒩,𝒞)
and Pr 𝒰𝒦
(𝒩,𝒞)
are the transmitted and received power of mBS 𝒦 𝒩
𝑡ℎ
respectively
which are controlled by operator 𝒩 𝑡ℎ
and operated at mmWave carrier frequency 𝒞; 𝐺𝑟
(𝒩,𝒞)
and
𝐺𝑡
(𝒩,𝒞)
are the directivity gains of the receiver and transmitter antennas in dBi, respectively.
To characterise the performance of each participating operator, we consider the 𝑆𝐼𝑁𝑅
as an indication to assess the outage probability as given in (4) [23]. We assume that any user
𝒰(𝑡ℎ,𝒩)
be in outage if the 𝑆𝐼𝑁𝑅 value is below than (𝑇ℎ𝑑 ≤ 0).
Ґ 𝒰𝒦
(𝒩,𝒞)
=
Pr 𝒰𝒦
(𝒩,𝒞)
∑ I 𝒰𝒦
(𝒩,𝒞)N
n=1 + η(𝒩,𝒞)
(4)
desired signal received by the receiver 𝒰 𝑡ℎ,𝒩
; η(𝒩,𝒞)
stands for the additive white noise power of
𝒩 𝑡ℎ
with respect to carrier frequency 𝒞.
Ґ 𝒰𝒦
(𝒩,𝒞)
calculation opens the way for further user channel capacity calculation utilising
Shannon capacity theory as expressed in (5) [24]:
𝔇 𝒰𝒦
(𝒩,𝒞)
= Ϥ 𝒦
(𝒩,𝒞)
× (
𝒲(𝒩,𝒞)
𝑎𝑙𝑙𝒰 𝒦
𝑡ℎ ) × 𝑙𝑜𝑔2
(1 + Ґ 𝒰𝒦
(𝒩,𝒞)
) , (5)
where Ϥ 𝒦
(𝒩,𝒞)
stands for the minimum number of antennas in the transmitter/receiver side;
𝒲 𝒩,𝒞 stands for the predefined amount of spectrum bandwidth allocated to 𝒩 𝑡ℎ
; 𝔇 𝒰𝒦
(𝒩,𝒞)
stands
for the channel capacity of 𝒰(𝑡ℎ,𝒩)
; 𝑎𝑙𝑙𝒰 𝒦
𝑡ℎ
stands for the number of UEs associated with
the serving 𝒦 𝒩
𝑡ℎ
.
2.3. Energy Efficiency (EE) Model
In the literature, the definition of EE varies according to the measured objects. In
a communication system, the generic energy efficiency calculation is modeled as the total sum
rate of the whole system divided by the total power consumption. However, as the objective of
this work is to maximize the EE for each individual UE-mBS link while maintaining a certain level
of QoE to the UEs, an efficient UA is involved to associate the user with the mBSs that provides
the best trade-off between rate provisioning and power consumption. Therefore, the EE is
defined in (6) as the number of achievable bits divided by the consumed energy (bits/Joule) for
the associated UE-mBS link represented by (𝒰𝒦) [25]:
𝐸𝐸 𝒰𝒦
(𝒩,𝒞)
=
𝔇 𝒰𝒦
(𝒩,𝒞)
𝑃 𝒰𝒦
(𝒩,𝒞), (6)
where 𝑃𝒰𝒦
(𝒩,𝒞)
is the total power consumption that consumed by the mBS which is equal to
(
Pt
(𝒩,𝒞)
µ
+ 𝑃𝐶𝑖𝑟𝑐𝑢𝑖𝑡
𝒦
); µ and 𝑃𝐶𝑖𝑟𝑐𝑢𝑖𝑡
𝒦
(0.25 and 0.1 mW) stands for amplifier efficiency and the circuit
power consumed by each mBS respectively.

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2.4. QoE-Based EE UA-FHSS Model
In this subsection, the most important QoE-Based EE UA-FHSS considerations are
meticulously addressed underlying four multi-independent 5G mmWave cellular operators that
share a chunk of its own spectrum bandwidth amongst each other based on a set of predefined
roles (i.e., FHSS). Each operator adopts the same roles to associate a typical UE belong to its
own operator (based on licensed spectrum access strategy) or to another operator (based on
semi-fully shared spectrum access strategy) with the tagged mBSs that provides the best
𝔇 𝒰𝒦
(𝒩,𝒞)
− 𝐸𝐸 𝒰𝒦
(𝒩,𝒞)
trade-off to enhance the energy efficiency while retain a certain QoE to
the UEs. More precisely, each operator 𝒩 𝑡ℎ
grants a licensed access to 250 MHz at 28 GHz
carrier frequency (when 𝒞 𝓂 = 0) to 𝒰(𝑡ℎ𝑠,𝒩)
which are subscribing to its own operator in order to
evade inter-operator interference. Meanwhile, in the high carrier frequency 73 GHz,
the spectrum (when 𝒞 𝓂 = 1) is divided into two portions, each with 500 MHz. The first portion
(500 MHz) is shared among all operators. The second one (500 MHz) is sliced into two chunks
each is assigned as semi-shared to only two operators. The first chunk (250 GHz) is granted to
OP1 and OP4, and the second to OP2 and OP3. Based on that, there are three options for
the UE (i.e., Raihana) to be associated with a particular 𝒦𝑡ℎ,𝒩 as illustrated in Figure 1. Such
association is performed based on the proposed QoE-Based EE UA-FHSS which makes
a decision to associate (Raihana) with mBS1-OP2 as it offers the best 𝔇 𝒰𝒦
(𝒩,𝒞)
− 𝐸𝐸 𝒰𝒦
(𝒩,𝒞)
trade-off.
The baseline (max-SINR UA-FHSS) is similar to the proposed QoE-Based EE UA-FHSS.
Unlike, the UE (i.e., Raihana) is associated with mBS that provides the highest SINR. Based
on the above-mentioned FHSS roles, we adopt both max-SINR UA-FHSS and QoE-Based
EE UA-FHSS schemes as illustrated in Algorithm 1 to associate the UEs with 𝒦 𝒩
𝑡ℎ
that offers
minimum energy consumption compared with the baseline max-SINR UA-FHSS which
associates the UEs with 𝒦 𝒩
𝑡ℎ
that offers max-SINR.
Figure 1. An illustration of EE UA FHSS scheme
Algorithm 1 Pseudocode of the implementation based on max-SINR and max-EE
mUA-FHSS schemes
Input: Set the initial parameters of ∀ 𝒩 𝑡ℎ
∊ 𝒩, ∀𝒦 𝒩
𝑡ℎ
∊ 𝒦, ∀𝒰(𝑡ℎ,𝒩)
∊ 𝒰, ∀ 𝒲 𝒩,𝒞, Pt
ℳ,𝑆κ, η(𝒩,𝒞)
,
𝐺𝑡
(𝒩,𝒞)
, 𝐺𝑟
ℳ,𝑆κ
.
1 Deployment of ∀𝒦 𝒩
𝑡ℎ
, ∀𝒰 𝑡ℎ,𝒩
all over the predetermined area (1.2 Km x 1.2 Km);
2 for ∀𝒰(𝑡ℎ,𝒩)
∊ 𝒰 & ∀ 𝒩 𝑡ℎ
∊ 𝒩 do
3 Calculate 𝑑 𝒰𝒦 of ∀𝒰 𝑡ℎ,𝒩
in terms of ∀𝒦 𝒩
𝑡ℎ
that belong to the same or to the shared
operator;
4 Calculate 𝑃𝐿𝑓𝑠(𝑑 𝑜), 𝑃𝐿𝑑 𝒰𝒦
(𝒩,𝒞)
, and Pr 𝒰𝒦
(𝒩,𝒞)
of ∀𝒰 𝑡ℎ,𝒩
by means (1), (2), a (3);
5 Calculate Ґ 𝒰𝒦
(𝒩,𝒞)
of ∀𝒰(𝑡ℎ,𝒩)
in terms of ∀𝒦 𝒩
𝑡ℎ
that belong to the same or the shared
operator (4);
max-SINR mUA-FHSS scheme max-EE mUA-FHSS scheme
6 Associates ∀𝒰(𝑡ℎ,𝒩)
to the serving 𝒦 𝒩
𝑡ℎ
Compute 𝔇 𝒰𝒦
(𝒩,𝒞)
according
to (5);

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that offers the highest Ґ 𝒰𝒦
(𝒩,𝒞)
;
7 Calculate 𝔇 𝒰𝒦
(𝒩,𝒞)
according
to (5);
8
9 end for
Calculate 𝐸𝐸 𝒰𝒦
(𝒩,𝒞)
according
to (6);
Associates ∀𝒰(𝑡ℎ,𝒩)
to the tagged 𝒦 𝒩
𝑡ℎ
that
offers the highest 𝐸𝐸 𝒰𝒦
(𝒩,𝒞)
;
end for
10 Calculate the average rate (𝐴𝑣𝑔𝔇𝒩), where 𝒩= {1,2,3… 𝑁};
11 Calculate the average EE (𝐴𝑣𝑔𝐸𝐸𝒩), where 𝒩= {1,2,3… 𝑁};
Output: average rate, average of EE, and CDFs of EE;
3. Results and Analysis
In this section, the performance of the proposed QoE-Based EE UA-FHSS is
numerically evaluated considering both dissimilar spectrum allocation and hybrid mBSs
deployment. Two main performance measures (average rate and energy efficiency) are adopted
in the evaluation process to compare the proposed QoE-Based EE UA-FHSS with the baseline
well-known max-SINR UA-FHSS. The related configurations and simulation parameter settings
are listed in Table 1.
3.1. Average Rate Assessment
Some numerical results are described in this subsection which brings a confirmation
that QoE-Based EE UA-FHSS achieves a good QoE to the UEs in terms of average rate via
optimally choosing of the best EE and rate provisioning trade-off. The average rate of the UEs
that are served by the four mmWave cellular operators based on the proposed QoE-Based EE
UA-FHSS and the baseline max-SINR UA-FHSS is depicted on Figure 2. It is shown that
a certain level of QoE (i.e., the average rate more than one gigabit per second) was achieved to
satisfy the needs of the future 5G applications, while gaining more enhancement in the overall
EE as will be discussed in the next subsection. Figure 2 also shows the superior performance of
the proposed QoE-Based EE UA-FHSS over the baseline mechanism in terms of achieving
higher data rate (more than two folds).
Multiple Operators
OP1 OP2 OP3 OP4
AverageRate(Gbps)
0.0
0.5
1.0
1.5
2.0
2.5
Average rate utilising max-SINR-Based UA-FHSS
Average rate utilising QoE-Based EE UA-FHSS
Figure 2. Average rate of the four participating
cellular operators using QoE-Based EE and
max-SINR-Based UA FHSS schemes
Table 1. Simulation Parameter Settings
Parameters Description/value
MmWave Base
Station Layout
Grid-based Cell
Deployment
MmWave Base
Station Density
16
Number of Operator 4
UE Density 160 Users
Area of Simulation 1.2 Km2
Inter-Site-Distance
(ISD)
300 m
mBS Carrier
Frequency
28GHz and 73GHz
mBS Transmit Power 30 dBm
Noise Figure (US) 6 dB
Variant of White
Gaussian Noise
-174 dBm/Hz
mBS Bandwidth 1GHz for 28GHz and
73GHz
3.2. Energy Efficiency Distribution
In this subsection, the focus of attention is to analyse the system performance in terms
of EE for all participating operators. Figures 3 (a-d) show the energy efficiency distribution of
OP1, OP2, OP3, and OP4 respectively. Notably, the proposed QoE-Based EE UA-FHSS
outperforms the most conventional max-SINR UA-FHSS mechanism in terms of EE distribution
where on average more than (90%) of the UEs that belong to the four operators
experience more than (100 Mb/Joule) compared to (45%) with the adoption of the baseline UA
(max-SINR UA-FHSS). Furthermore, as depicted in Figure 4, the average of EE of the four

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multi-independent 5G mmWave cellular operators utilizing QoE-Based EE UA-FHSS
significantly outweighs the baseline max-SINR UA-FHSS. More precisely, it was realized that
the average of EE of each participating operator is more than (350 Mb/Joule), achieving
an improvement more than two-fold over the baseline UA. This resulted from the enhancement
of the experienced rate.
Figure 3. A comparison of the CDFs of EE of the four mmWave cellular operators
utilising both our proposed QoE-Based EE-FHSS and the baseline max-SINR UA-FHSS
(a) OP1, (B) OP2, (c) OP3, (d) OP4
Multiple Operators
OP1 OP2 OP3 OP4
AverageofEE(Mb/Joule)
0
100
200
300
400
500
600
Max-SINR-Based UA-FHSS
QoE-Based EE UA-FHSS
Figure 4. Average of energy efficiency of the four operators utilizing
QoE-Based EE UA-FHSS and max-SINR UA FHSS

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4. Conclusion
In this article, green and QoE-Based UA involving spectrum sharing approach is
presented considering multi-independent 5G mmWave cellular operators. Three spectrum
access strategies (licensed, semi-shared and fully-shared) are integrated in a hybrid manner to
provide an order of magnitude enhancement in both spectrum utilisation and individual UE-mBS
energy consumption. The numerical results show that such hybrid integration with its own
nature (i.e., diversity) can effectively enhance the data rate by means of reducing the mutual
interference issues amongst the participating operators. Furthermore, the utilization of
the proposed QoE-Based EE UA-FHSS attains considerable improvement in EE compared with
the max-SINR-Based UA-FHSS. The EE of the four mmWave cellular operators with
the adoption of QoE-Based EE UA-FHSS are improved with more than two folds over
the baseline max-SINR-Based UA-FHSS. Moreover, it enables a rapid creation of new wireless
applications or merging more than one operator (i.e. MergedCo) in a cost-effective manner due
to the reduction of operation expenditure (OpEx). In future work, we will expand this analysis by
means of involving more complex UA mechanism such as multi criteria decision-making
approach considering diverse services and applications requirements.
Acknowledgments
The authors gratefully acknowledge UTeM Zamalah Scheme, Universiti Teknikal
Malaysia Melaka (UTeM), and the Center for Research and Innovation Management (CRIM),
Center of Excellence, Universiti Teknikal Malaysia Melaka (UTeM).
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