This document summarizes research on improving the capacity of cellular systems using fractional frequency reuse (FFR). It discusses how frequency reuse is used to increase the number of users that can be served but causes interference, particularly for cell edge users. Fractional frequency reuse is proposed to solve this problem by allocating different frequency sets to cell center and edge users to reduce interference. The document also reviews different types of interference (co-channel and adjacent channel) and how power control can help reduce interference in cellular systems.

1. Int. Journal of Electrical & Electronics Engg. Vol. 2, Spl. Issue 1 (2015) e-ISSN: 1694-2310 | p-ISSN: 1694-2426
NITTTR, Chandigarh EDIT -2015 172
Capacity Improvement of Cellular System
Using Fractional Frequency Reuse (FFR)
1
Gyan Prakash Pal, 2
Sadhana Pal
1
M.E. Scholar, ECE Department, NITTTR, Chandigarh, India
2
Assistant Professor, ECE Department, VGI, Greater Noida, India
Abstract:- Today wireless communication is mostly used
rather than wired communication, due to remote location
reach ability, less fault occurrence, less time to commissioning
and low cost etc. But wireless network has less frequency
spectrum to cover the whole world. To improve the capacity
of cellular system in a limited spectrum without major
technological changes, frequency is reused in cells. But it
offers interferences mostly for cell edge users. To solve the
problem of spectral congestion and user capacity, fractional
frequency reuse is used. This paper gives idea about different
frequency reuse factors, fractional frequency reuse and super
cell with sectoring to improve the capacity of cellular system.
Keywords: Frequency reuse factor, Frequency reuse ratio,
Interference, Co-channel interference, Adjacent channel
interference, Fractional frequency reuse, Signal-to-interference
ratio
I.INTRODUCTION
Enable a fix number of channels to serve an arbitrarily
large number of users by reusing the channel throughout
the coverage region. Effective reuse of resources can
highly enhance the system capacity. Frequency reuse factor
(FRF) N defines frequency reuse pattern
= + + (1)
Where i and j are non-negative integers.
Figure 1: Cell arrangements with reuse factor
With a smaller frequency reuse factor (FRF), N more
available bandwidth can be obtained by each cell. With the
usage of FRF-1, the most user terminals (UTs) are afflicted
with heavy Inter-cell interference (ICI). Especially near the
cell edge. The conventional method to figure out this
problem is by increasing the FRF which mitigate the ICI
efficiently but decrease on available bandwidth in a cell.
The most representative approaches improving cell-edge
performance while retaining spectrum efficiency by
Fractional Frequency Reuse (FFR).
Figure 2: Interference for cell edge users
II. LITERATURE SURVEY
The initial search procedure in WCDMA is used to identify
the scrambling code used by the base station that has the
lowest path loss coefficient of the received signal among
all the other base stations. The timing relationship between
base stations is asynchronous in W-CDMA system. So the
three-step cell search algorithm is introduced in 3GPP
protocols in order to fast identify the special base station.
The second step, Secondary Synchronous Channel(S-SCH)
acquisition, is much critical. We have focused on the
second step of the initial search procedure: frame
synchronization and code-group identification. We propose
partial correlation method, which extremely reduces the
hardware complexity. This method minimizes the
acquiring time of the scrambling code group further used
for identify the scrambling code of the selected base
station. [7]
Wireless Sensor Network (WSN) has specific constraints
and stringent requirements in contrast to traditional wired
and wireless computer networks. Due to the wide potential
applications of wireless sensor networks, this topic has
attracted great attention. The strict energy constraints of
sensor nodes result in great challenges for energy
efficiency. Because of limitation in energy and selection of
best route, for the purpose of increasing network remaining
energy a node with most energy level will be used for
transmission of data. The most part of energy in nodes is
wasted on radio transmission, thus decreasing number of
transferred packets in the network will result in increase in
node and network lifetimes.
This paper proposes an energy-efficient organization
method. The organization of wireless sensor networks is
formulated for target tracking. The destination route is
achieved by collaborative sensing with multi-sensor fusion.
The sensor nodes implement sensing tasks are awakened in
a distributed manner. Thus, by using this we can be

2. Int. Journal of Electrical & Electronics Engg. Vol. 2, Spl. Issue 1 (2015) e-ISSN: 1694-2310 | p-ISSN: 1694-2426
173 NITTTR, Chandigarh EDIT-2015
minimized energy consumption in wireless sensor network.
[8][10]
The network developed after integrating the various
wireless technologies is called heterogeneous network.
This growth of available broadband access technology has
brought enormous challenges for operators wanting to
ensure seamless mobility to its customer in heterogeneous
environment. In this paper, we proposed a possible UMTS-
WIMAX internetworking architecture and the VHO
protocol based on MIH (IEEE 802.21 standard) for UMTS
and WIMAX heterogeneous network for seamless inter-
system handover, services continuity with low handover
latency, system throughput and packet loss. The handover
procedure is based on the media independent handover
function (MIHF) which is guided by MIIS server. [9]
This paper presents the features of the Worldwide
Interoperability for Microwave Access (WiMAX)
technology and future applications of WiMAX. A
discussion is given by comparing WIMAX with DSL
(Digital subscriber line) & Cable and Wireless Fidelity
(Wi-Fi). Several references have been included at the end
of this paper for those willing to know in detail about
certain specific topics. [11] [12]
5G technologies will change the way most high-bandwidth
users access their phones. With 5G pushed over a VOIP-
enabled device, people will experience a level of call
volume and data transmission never experienced before.5G
technology is offering the services in Product Engg.,
Documentation, supporting electronic transactions (e-
Payments, e-transactions) etc. As the customer becomes
more and more aware of the mobile phone technology, he
or she will look for a decent package all together, including
all the advanced features a cellular phone can have. Hence
the search for new technology is always the main motive
of the leading cell phone giants to out innovate their
competitors. The ultimate goal of 5G is to design a real
wireless world that is free from obstacles of the earlier
generations. This requires an integration of networks. [16]
III. INTERFERENCE
Interference is the major limiting factor in the performance
of cellular radio systems. Interference on voice channels
causes crosstalk and on control channels, interference leads
to missed and blocked calls due to errors in the digital
signaling.
Two major cellular interferences are:
1. Co-channel interference
2. Adjacent channel interference
1. Co-channel Interference
Frequency reuse pattern give the coverage area with
several cell that use the same set of frequencies. These
cells are called co-channel cells, and the interference
between signals from these cells is called co-channel
interference. To reduce co-channel interference, co-
channel cells must be physically separated by a minimum
distance to provide sufficient isolation due to propagation.
When the size of the each cell is approximately the same
and the base stations transmit the same power, the co-
channel interference ratio is independent of the transmitted
power and becomes a function of the radius of the cell (R)
and the distance between centers of the nearest co-channel
cells (D). By increasing the ratio of D/R, the spatial
separation between co-channel cells relative to the
coverage distance of a cell is increased. Thus interference
is reduced from improved isolation of RF energy from the
co-channel cell. The parameter Q, called the co-channel
reuse ratio, is related to the cluster size. For a hexagonal
geometry
(2)
A small value of Q provides larger capacity since the
cluster size N is small, whereas a large value of Q
improves the transmission quality, due to a smaller level of
co-channel interference. A trade-off must be made between
these two objectives in actual cellular design.
Table 1: Co-channel reuse ratio and SIR for some value of
N
Cluster Size
(N)
Co-channel Reuse
ratio (Q)
I = 1, j = 1 3 3
I = 1, j = 2 7 4.58
I = 2, j = 2 12 6
Let io be the number of co-channel interfering cells. The
signal-to-interference ratio (SIR) for a mobile receiver can
be expressed as
=
∑
(3)
Considering only the first layer of interfering cells, if all
the interfering base stations are equidistant from the
desired base station and if this distance is equal to the
distance D between cell centers, then equation (3)
simplifies to
=
( / )
=
√
(4)
S: the desired signal power from the desired base station
Ii: interference power caused by the ith
interfering co-
channel cell base station
Signal-to-interference ratio for the worst case can be
=
( ) ( )
(5)
Or
=
( ) ( )
(6)
2. Adjacent Channel Interference
Interference resulting from signals which are adjacent in
frequency to the desired signal is called adjacent channel
interference. Adjacent channel interfere results from
imperfect receiver filters allow nearby frequencies to leak
into the pass band. Adjacent channel interference can be
minimized through careful filtering and channel
assignment. Keep the frequency separation between each
channel in a given cell as large as possible. A channel
separation greater than six is needed to bring the adjacent
channel interference to an acceptable level.
N
R
D
Q 3

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NITTTR, Chandigarh EDIT -2015 174
Figure 3: Adjacent channel interference
IV. POWER CONTROL FOR REDUCING
INTERFERENCE
In practical cellular radio and personal communication
systems, the power levels transmitted by every subscriber
unit are under constant control by serving base stations.
Ensure each mobile transmits the smallest power necessary
to maintain a good quality link on the reverse channel
Power control helps on:
 long battery life
 decrease SIR
 solve the near-far problem
V. IMPROVING CAPACITY IN CELLULAR
SYSTEMS
Methods for improving capacity in cellular systems are:
 Cell Splitting: subdividing a congested cell into
smaller cells. Reduce transmission power.
 Sectoring: directional antennas to control the
interference and frequency reuse.
 Fractional frequency Reuse (FFR)
VI. FRACTIONAL FREQUENCY REUSE (FFR)
There are different methods to use fractional frequency
reuse:
i. Frequency reuse factor 1
 Same frequency is reused by each sector
 High spectral efficiency
 Large inter-cell interference
 Cell edge users can rarely retain connection
Figure 4: Frequency Reuse Factor 1
ii. Frequency reuse factor 3
 Same frequency is reuse every 3 sectors
 Low spectral efficiency
 Low inter-cell interference
 Cell edge users have fairly good connection
quality
Figure 5: Frequency Reuse Factor 3
iii. Different frequency reuse factor in one sector
 Sector edge band using frequency reuse 3,
allocated to the cell edge users
 Sector center band using frequency reuse 1,
allocated to the users in the center of the
sector
Figure 6: Frequency Reuse Factor 1 and 3
iv. Soft Fractional Frequency Reuse
 To compensate the spectral efficiency loss
due to fractional frequency reuse
 The reserved band at each sector is allocated
for center users with restricted power
Figure 7: Soft Fractional Frequency Reuse
v. Dynamic Fractional Frequency Reuse
 Dynamic fractional frequency reuse
 The ratio of sector center and sector edge
bands is adaptive to traffic load, user
distribution, etc.
desired signal
receiving filter
response
desired signal
interference
interference
signalon adjacentchannelsignalon adjacentchannel
FILTER

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175 NITTTR, Chandigarh EDIT-2015
Figure 8: Dynamic Fractional Frequency Reuse
VII. SIMULATION RESULTS
Fig. 9: Comparison of dynamic and soft FFR schemes
Fig. 10: Performance improvement of cell edge users
VIII. CONCLUSION
Fractional frequency reuse (FFR) scheme should be
supported to improve average and cell-edge user
throughput. The ratio of different frequency reuse factor
and the corresponding power level are optimized or
adjusted adaptively according to the traffic load and user
distribution, etc., to trade of between spectral efficiency
and average/cell-edge user throughput enhancement.
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