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OVERVIEW

This proposal looks to
give insight about the Enhanced Fractional Frequency Reuse technique in cellular
networks particularly Long Term Evolution (LTE) network. LTE is a wireless communication
for mobile devices. It is based on the GSM/EDGE and UMTS/HSPA technologies. It increases the capacity and speed using
a different radio interface together with core network improvements. The
standard is developed by the 3rd Generation Partnership Project (3GPP).

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EFFR technique will sort to minimize
interference in LTE communication thereby allowing to sufficiently efficiently accommodate
all users. In addition to that this technique also help to improve the
performance of cellular network by improving the cell coverage range.

 

INTRODUCTION

In mobile cellular
systems the frequency resource is often reused repeatedly over some
geographical location i.e. frequency allocated to a desired cell is reallocated
repeatedly different cell from another cluster separated by a large enough
interval. This will contain radio interference levels to desirable range.

Figure 2
frequency reuse (source http://www.raymaps.com/wp-content/uploads/2011/12/reuse.jpg)

 

Fractional Frequency
Reuse is a technique deployed in Orthogonal Frequency Division Multiple Access
to reduce ICI and CCI. FFR can be static or dynamic. In static FFR the
Frequency Reuse Factor is allocated is greater than one in the neighboring
cells while in Dynamic an intelligent scheduler is deployed. Static method is
the broadly used method as it has low load signaling overhead and less complex. 1

Orthogonal Frequency
Division Multiple Access is a scheme used to achieve high data communication
speed. OFDMA uses a 15 KHz subcarrier in the LTE network and each of these subcarriers
are collectively known as Resource Blocks. Each RB has 12 subcarriers
equivalent to 180 KHz. 1

OFDMA FFR divides both
time and frequency resources into sub-bands to alleviate interference, can be
used in both Up Link and Down Link but mostly used in Downlink channels.

OFDMA works by dividing
the radio cell into 2 regions: namely the inner and outer. Inner regions are
regions that are close to the Base Station. The outer region is located to the
cell edges. The whole frequency band has to be divided into sub-bands in order
to allocate frequencies to these regions. 1

 

LITERATURE
REVIEW

There’s already a number techniques
for the reduction of Inter-Cell Interference which includes Fractional
Frequency Reuse and Soft Frequency Reuse (SFR)

One of these schemes is
called the Soft Frequency Reuse. In SFR the
available frequency spectrum in a network can be reused in each cell. The cell
is divided into two regions, major and minor. The major region subcarriers are
capable of serving the users located in both major and minor cell regions. In
these adjacent cells these sub-carriers are orthogonal 4

Fig 2
below  shows that in SFR given bandwidth
is divided in three parts, higher power density level frequency band, that is
also called primary band which is used at cell edge and other two bands with
low power density level are called secondary bands. At the cell center whole
available bandwidth is used and at cell edge high power density frequency bands
are used. As primary bands are orthogonal to each other so interference at cell
edge is minimum that will enhance the overall system throughput 4

Figure
3 SFR technique (source http://0-ieeexplore.ieee.org.biulms.biust.ac.bw/document/8068542/)

Limitations of SFR scheme

·        
Less number of cell center users compared
to cell edge users(less interference at cell edges)

 

PROBLEM DEFINITION

One of the biggest
problems that cellular networks performance are faced with is the need to
increase capacity. This poses a problem of high levels of attenuation of Inter
Cell Interference (ICI) and Co-Channel Interference (CCI) at cell edges of the
same operation frequency and from neighboring base stations. ICI occurs between
neighboring cells while CCI occurs between adjacent channels. This winds up
causing uneven distribution of throughputs of User Equipment.

ICI affects performance of
the cell edges causing loss of data packets. This then requires retransmission
of lost packets, the constant retransmission of lost packets hence leads to a
reduced performance by the network 2

 

PROBLEM STATEMENT

The challenge of Inter Cell Interference in cellular
network is major challenge for both users and network providers.  ICI is caused
by neighboring cells using the same frequency band. 

For users it ICI implies
a limited number of services due to the reduced network performance which hence
leads them to frustrations. Bad user experience means declined number of users
hence losses to the network provider. ICI also poses a problem for network
providers as they have to come up with techniques which can be used to reduce
interference and improve coverage. These techniques can be quite costly.

 

Figure 4
Bae Stations and Cell EDGES (source http://media.springernature.com)

PROPOSED SOLUTION

Technique called Enhanced Fractional Frequency Reuse
which an interference avoidance and is aimed at reducing Inter Cell
Interference in order to improve cell coverage and cell capacity. The scheme
will divide the whole subcarriers into groups which are orthogonal and assigned
to cells transmitter power and patterns which are varying. To avoid ICI an
Interference Avoidance Factor is defined. To match the number of users the
number of allocated subcarriers is adjusted.

Advantages of EFFR Scheme

·        
More robust and more flexible than the
currently used scheme of Soft Frequency Reuse (SRF)

·        
Effectively reduces the levels of ICI

·        
Improved performance for cell edge users

 

 

PROJECT
OBJECTIVES:

·        
To minimize Inter Cell Interference
challenge in LTE communication (improve network performance)

·        
To increase cell coverage thereby allowing
an increase in capacity

·        
To increase rate of production
(throughput) of user equipment

 

Problem
Decomposition

EFFR’s objective is to
improve the system capacity while improving spectral efficiency at the edges of
the cells

EFFR is an improvement to
the current Soft Frequency Reuse technique as it had limitation being that
there are less cell center users than cell edge users

 

DESIGN METHODOLOGY

Frequency Reuse is a
technique of reusing frequencies and channels within a system of communication
to improve spectral efficiency and capacity

Techniques used to
expanding an already existing network

a.      
Cell splitting-a process of sub-diving
cells into smaller cells

b.     
Cell sectoring-replacing a single
omnidirectional antenna by directional antennas each emitting within a
specified location

 

Reuse Partition

EFFR partitions describes
3cells types for directly neighboring cells in cellular system. It also leaves
a reserve for each cell type as part of the whole frequency band. This is
called the Primary Segment, it should be orthogonal among different type of
cells. The remaining sub-channels make up the Secondary Segment. The Primary
Segment of a cell type is also part of the secondary segment belonging to the
other 2 cell types with each cell capable of occupying all sub-channels of the
Primary Segment. 3

The Primary Segment of
each cell is further divided into reuse 3 part and reuse 1 part with reuse 1
part being able to be reused by all types of cells in the system. The reuse
3part can only solely be reused by other similar cell types (reuse 3
sub-channels can’t be used by directly neighboring cells which attenuates the
ICI among them) 3

 

Figure 5 EFFR scheme 4

 

CQI-Channel Quality
Indicator

 

PROJECT PLAN AND
SCHEDULE

The project is
partitioned into 2 stages namely Project I and Project II.

Project I – starts form
December 2017 to March 2018(semester 1) and is basically comprehension of the
project title as well as learning about the resources and hardware needed to
complete the project. A simulation model shall also be carried out during this
stage. During this stage a project proposal shall be drafted and presented to a
panel of judges.

Project II-starts from
May to October 2018 and entails the actual design and experimentation of the project.

 

 

 

 

 

 

SCHEDULE FOR PROJECT I
(01 Dec – March 2018)

 

Activity

Start
Date

Duration(days)

Topic
allocation

01
December 2017

1

Obtaining
Sources

02
December 2017

1

Evaluation
of Sources

03
December 2017

1

Literature
review

04
December 2017

14

Design
methodology and software

10
December 2017

3

Preparation
of proposal

16
December 2017

35

Presentation
of proposal

11
January 2018

1

Interim
report

25
January

1

Final
report presentation

25
March 2018

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

RESOURCES

Software:

·        
Atoll Software Simulator

·        
Mat lab           

Hardware:

·        
Computer

 

 

WORKS
CITED

1

U. K. U. S. P. W.
Mayangasari Nur Almusawwir, “Analysis of LTE network planning with
multi-level soft frequency reuse : Cimahi City case study,” in IEEE,
Yogyakarta, Indonesia, 2017.

2

S. K. A. W. R. A. M.
G. T. A. L. Mohammad Nour Hindia, “Frequency Reuse for 4G Technologies:
A Survey,” in 2Qatar Mobility Innovations Center, Qatar, 15
January 2015..

3

R. A. A. Y. J. A.
A.-D. Z. I. M Salman, “Enhanced Fractional Frequency Reuse(EFFR)
tECHNIQUE in Wimax Cellular Network,” International Journal of
Computer Science Issues, vol. 9, no. 6, pp. 84-86, 2012.

4

B. W. Zheng Xie,
“Enhanced Fractional Frequency Reuse to,” in 2009 3rd
International Conference on New Technologies,Mobility and Security,
Cairo, Egypt, 2009.

 
 

 

 

 

 

 

 

 

REFERENCES

1

U. K. U. S. P. W.
Mayangasari Nur Almusawwir, “Analysis of LTE network planning with
multi-level soft frequency reuse : Cimahi City case study,” in IEEE,
Yogyakarta, Indonesia, 2017.

2

S. K. A. W. R. A. M.
G. T. A. L. Mohammad Nour Hindia, “Frequency Reuse for 4G Technologies:
A Survey,” in 2Qatar Mobility Innovations Center, Qatar, 15
January 2015..

3

R. A. A. Y. J. A.
A.-D. Z. I. M Salman, “Enhanced Fractional Frequency Reuse(EFFR)
tECHNIQUE in Wimax Cellular Network,” International Journal of
Computer Science Issues, vol. 9, no. 6, pp. 84-86, 2012.

4

B. W. Zheng Xie,
“Enhanced Fractional Frequency Reuse to,” in 2009 3rd
International Conference on New Technologies,Mobility and Security,
Cairo, Egypt, 2009.

 

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