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Survey of ICIC Techniques in LTE Networks under
Various Mobile Environment Parameters
Mohamad Yassin, Mohamed A. Aboulhassan, Samer Lahoud, Marc Ibrahim,
Dany Mezher, Bernard Cousin, Essam A. Sourour
To cite this version:
Mohamad Yassin, Mohamed A. Aboulhassan, Samer Lahoud, Marc Ibrahim, Dany Mezher, et al..
Survey of ICIC Techniques in LTE Networks under Various Mobile Environment Parameters. Wireless
Networks, Springer Verlag, 2017, 23 (2), pp.403-418. �10.1007/s11276-015-1165-z�. �hal-01198389�
1
Survey of ICIC Techniques in LTE Networks
under Various Mobile Environment Parameters
Mohamad Yassin
‡∗
, Mohamed A. AboulHassan
§
, Samer Lahoud
‡
, Marc Ibrahim
∗
,
Dany Mezher
∗
, Bernard Cousin
‡
, Essam A. Sourour
∗∗
‡
University of Rennes 1, IRISA, Campus de Beaulieu, 35042 Rennes, France
∗
Saint Joseph University of Beirut, ESIB, CST, Mar Roukoz, Lebanon
§
Pharos University, Electrical Engineering Department, Alexandria, Egypt
∗∗
Prince Sattam Bin Abdul-Aziz University, Wadi Addawasir, Saudi Arabia
Abstract
LTE networks’ main challenge is to efficiently use the available spectrum, and to provide satisfying
quality of service for mobile users. However, using the same bandwidth among adjacent cells leads
to occurrence of Inter-cell Interference (ICI) especially at the cell-edge. Basic interference mitigation
approaches consider bandwidth partitioning techniques between adjacent cells, such as frequency reuse
of factor m schemes, to minimize cell-edge interference. Although SINR values are improved, such
techniques lead to significant reduction in the maximum achievable data rate. Several improvements
have been proposed to enhance the performance of frequency reuse schemes, where restrictions are
made on resource blocks usage, power allocation, or both. Nevertheless, bandwidth partitioning methods
still affect the maximum achievable throughput. In this proposal, we intend to perform a comprehensive
survey on Inter-Cell Interference Coordination (ICIC) techniques, and we study their performance while
putting into consideration various design parameters. This study is implemented throughout intensive
system level simulations under several parameters such as different network loads, radio conditions,
and user distributions. Simulation results show the advantages and the limitations of each technique
compared to frequency reuse-1 model. Thus, we are able to identify the most suitable ICIC technique
for each network scenario.
Index Terms
Inter-Cell Interference Coordination, mobile networks, LTE, frequency reuse-3, FFR, SFR.
2
I. INTRODUCTION
Third Generation Partnership Project (3GPP) introduced Long Term Evolution (LTE) [1]
standard to fulfill the increasing demand for data in mobile networks. LTE is a mobile network
technology that substantially improves end-user throughputs [2], in order to meet the rapid
growth in data demands. With the proliferation of mobile applications and the development
of mobile equipment industry, mobile operators always seek to increase resource efficiency in
order to make maximum use of the scarce available frequency spectrum. LTE chooses frequency
reuse-1 model to improve system capacity and increase user satisfaction. Multiuser Orthogonal
Frequency Division Multiple Access (OFDMA) [3] technique used for the radio interface on
the downlink of LTE networks eliminates intra-cell interference, since data is transmitted over
independent orthogonal subcarriers. Similarly, Single Carrier Frequency Division Multiple Access
(SC-FDMA) technique, characterized by a lower peak-to-average power ratio [4], is used on the
uplink to transmit data from users to the base station [5]. However, frequency reuse factor
one leads to Inter-Cell Interference (ICI) strongly affecting SINR of active User Equipments
(UEs), especially cell-edge UEs, which leads to a significant degradation in the total throughput.
Moreover the existence of network elements with different maximum transmission power, e.g.,
macrocells, picocells and femtocells, makes the ICI problem more complicated.
ICI arises as a prohibitive problem due to simultaneous transmissions over the same frequency
resources in adjacent LTE cells. ICI decreases Signal-to-Interference plus Noise Ratio (SINR)
especially for cell-edge UEs [6], that are relatively far from the serving evolved-NodeB (eNodeB).
Thus, it has a negative impact on user throughput, it decreases spectrum efficiency, and it reduces
the quality of provided services.
Hard frequency reuse schemes (e.g., reuse factor m) become inefficient due to utilization of
1
m
of available bandwidth that affects peak data rate. For instance, adjacent base stations of a
Global System for Mobile communications (GSM) network are allocated different frequencies
[7] in order to avoid interference between neighboring transmitters. A number of adjacent GSM
cells are grouped into a cluster where the same frequency resources are used only once [8]. A
cluster size of one is not used due to high co-channel interference problems that occur. Although
ICI within each cluster is eliminated, spectral efficiency is largely reduced.
In Code Division Multiple Access (CDMA) scheme, the interference experienced by a user
3
is due to cross-correlation between spreading codes, and it can be considered as noise [9].
Therefore, ICI problems do not exist in CDMA-based 3G networks. OFDMA scheme [10] is
based on OFDM technology that subdivides the available bandwidth into a multitude of narrower
mutually orthogonal subcarriers, which can carry independent information streams. A physical
Resource Block (RB) is defined as 12 subcarriers in the frequency domain (180 kHz) and six
OFDM symbols in the time domain, which is equivalent to one time slot (0.5 ms) [11]. RB
and power allocation are performed periodically by the schedulers every Transmit Time Interval
(TTI) that equals one millisecond.
Although frequency reuse-m models eliminate ICI, they are not adequate for LTE networks.
In fact, one major objective of 3GPP LTE standard is to increase network capacity in order
to accommodate additional UEs. According to reuse-m schemes, each base station is allowed
to allocate a portion of the available spectrum. This restriction is not tolerated in LTE since
it greatly reduces spectrum efficiency. Thus, other frequency and power allocation schemes are
used to reduce ICI; they are commonly known as Inter-Cell Interference Coordination (ICIC)
[12] techniques.
Fractional Frequency Reuse (FFR) [13] and Soft Frequency Reuse (SFR) [14] are distributed
static ICIC techniques used to improve spectral efficiency of LTE. While FFR sets restrictions
on RB allocation between the different UEs in each cell, SFR performs both radio resource
management and power allocation for the used RBs. These techniques are independently used
in each cell without any cooperation between adjacent base stations. Several works exploit the
communications between adjacent eNodeBs to reduce ICI. In fact, signaling messages about
RB and power allocation are exchanged between adjacent eNodeBs over X2 interface, that
interconnects neighboring cells. For instance, a recently proposed technique divides ICIC problem
into a multi-cell scheduling and a multi-user scheduling problem [15]. The former uses an On/Off
approach to determine the restricted RBs for each evolved NodeB (eNodeB), while the latter
attributes RBs to UEs according to their radio conditions. ICIC can also be seen as a cooperative
problem where LTE base stations collaborate in order to find the power allocation mask that
minimizes inter-cell interference [16]. It is an adaptive SFR scheme that reduces transmission
power on RBs allocated for UEs that experience good radio quality (close to the base station).
However, the time scale of the proposed algorithm is in order of tens of seconds, which is
disadvantageous when the system state is quickly varying with time.
4
With the introduction of Coordinated Multi-Point (CoMP) transmissions [17] in LTE-Advanced
(LTE-A) networks, ICIC techniques rely more on dynamic coordination between base stations.
Scheduling decisions are improved when they are made jointly for a cluster of cells [18] thereby
enhancing performance through interference avoidance. Small cells (including pico-cells, femto-
cells and home eNodeBs) deployment [19] along with existing macro base stations brings out the
challenge of ICIC in heterogeneous networks. Indeed, serious interference [20] problems occur
due to co-channel deployments with the macro cells. Enhanced-ICIC (e-ICIC) techniques are
used to allow for time-sharing of spectrum resources between macro base stations and small cells.
Authors of [21, 22] surveyed the different ICIC techniques, and they classified them according
to cell cooperation and frequency reuse patterns. However, some of the existing ICIC surveys
only present qualitative comparisons [23] of ICIC techniques, while others perform simulations
under uniform UE distributions and ordinary network scenarios.
Given the diversity of existing ICIC techniques, mobile network operators have the opportunity
to implement the most convenient one for their intended objectives. In fact, the performance of
some techniques largely depends on network parameters such as UE distribution between cell
zones, existing ICI problems, and the number of UEs in each cell. Some techniques aim at
improving cell-edge UEs throughput, without taking into account the overall spectral efficiency.
Consequently, the knowledge of ICIC techniques performance is a critical factor when selecting
the one that best fits operator’s goals. In this article, we perform a comprehensive survey of
the performance of ICIC techniques in LTE Networks. Various network loads, radio conditions,
and user distributions are considered, in order to study the impact of design parameters on ICIC
techniques performance. We investigate the performance of frequency reuse-m model and other
ICIC techniques, and we classify them depending on the cooperation between network base
stations. A MATLAB-based LTE downlink system level simulator [24, 25] is used to compare
the performance of frequency reuse-1 model with reuse-3 model, FFR and SFR techniques. The
objective of ICIC is to reduce interference problems in order to avoid their harmful impact on
user throughput and system performance. An efficient ICIC technique improves both spectral
efficiency and energy efficiency of the mobile network, which is a substantial goal for mobile
network operators.
The rest of the article is organized as follows: in section II we explain frequency planning
techniques used in GSM networks, we discuss interference problems in LTE, and we classify
