An approach to control inter cellular interference using load matrix in multi carrier mobile communication systems

IJRET: International Journal of Research in Engineering and Technology eISSN: 2319-1163 | pISSN: 2321-7308
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Volume: 04 Issue: 02 | Feb-2015, Available @ http://www.ijret.org 483
AN APPROACH TO CONTROL INTER CELLULAR INTERFERENCE
USING LOAD MATRIX IN MULTI CARRIER MOBILE
COMMUNICATION SYSTEMS
Srinivas Karedla1
, Santhi Rani2
1
Assistant Professor, Department of Electronics and Communications, GITAM University, Visakhapatnam, India
2
Professor, Department of Electronics and Communications, DMSSVH College of Engineering, Machilipatnam, India
Abstract
This paper deals with reduction of inter cellular interference in Multi-carrier communication systems. In the past, Load
Matrix(LM) is proposed to allocate power to different users in a network based upon Signal to noise plus interference ratio
(SNIR) so as to reduce inter cellular interference and is observed for single carrier systems. In Multi carrier systems the SNIR is
affected distinctly in each carrier thus a single SNIR for power allocation is not optimal. In this paper, to obtain the optimization
of power allocation in Multi-Carrier system, Load Matrix coding with bifurcated SNIR (LM-BFSNIR) is proposed. Using this
approach it is observed that inter cellular interference is reduced better when compared to a single carrier system evaluated over
a 3GPP-LTE standard.
Keywords−Power allocation, Inter cellular interference, Multi-Carrier mobile Communication system.
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1. INTRODUCTION
The objective of wireless communication systems is to offer
secured transmission by maximizing the data rate. To
achieve this aim modern technologies in wireless
communications are introduced in which multi-Carrier
communication is thriving at a rapid rate. Typically, for
higher data rate transmission extra band width is required.
Yet, because of spectral limitations ,it is usually absurd or
very expensive to rise bandwidth. The alternative solution is
to use multiple transmit and receive antennas for
deployment of available spectrum. Usage of multiple
transmit and receive antennas forms a multi-carrier
communication system. Advantages of multi-carrier over
single carrier are fine quality of service, less fraction of
dropped calls and more capacity of network . Capacity of a
network can be improved if multiple receive and transmit
antennas are used as multi carrier channels [1]. In [2] it is
shown thatmulti-carrier systems do better than the single
carrier with Rayleigh flat fading . Capacity of a multi carrier
system depends upon the number of receive and transmit
antennas. In Multi-carrier [3] by partitioning the entire
channel ( spectrum ) to many narrow parallel sub channels
so that width of symbol increases and thus reducing the inter
symbol interference generated by the multipath. In [4] it is
shown that co-channel interference is decreased by using
adaptive resource scheme in multi-carrier system. LM [5] is
a resource allocation scheme that allocates the power to the
available base stations and users based on the SNIR to
minimize inter cellular interference in turn reduce bit error
rate as outlined in the section I and is evaluated only for
single carrier systems .In multi carrier systems the SNIR is
affected distinctly in each carrier and hence by using a
diverse approach ie LM with bifurcated SNIR (LM-
BFSNIR) the bit error rate can be decreased better in multi
carrier than single carrier in reducing the inter cellular
interference better.In this paper the proposed LM-BFSNIR
approach is applied to multi carrier over 3GPP LTE
standards .
2. SYSTEM OUTLINE
Multi-Carrier technology has procured much significance
and users consideration because of its applications in
mobile communication, digital television, wireless LAN’s
and MAN’s. The channel capacity of multi-carrier system is
directly proportional to transmitter and receiver arrays,
which have been increased remarkably in multi carrier
system. Second, system performance and accuracy have
been enhanced in multi-carrier system as a result it provides
a spatial variety in which each transmitting signal is detected
by the whole detector array. This also minimizes the ISI
(inter symbol interference) effect and impact of channel
fading since each signal is determined based on ‘N’ detected
results i.e. spatial diversity offers ‘N’ independent replicas
of transmitted signal. Third advantage of multi carrier
system is that the array gain can be increased, which implies
that SNR gain can be obtained by increasing directivity i.e.
by focusing energy in required direction.
A Multi carrier system is designed for test evaluation with
four transmit and receive antennas is developed.
Transmitted data block can be defined as,
These signals are two different signals
for m=1 and 2
respectively through two space–time encoders. The mth
transmitting antenna signal is modulated by at the
oth
carrier of the rth
data block. The received signal is a

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superposition of four distorted transmitted Signals at each
receiving antenna, given by
(1)
For where is the additive complex
Gaussian noise at the nth
receive antenna, and is assumed to
be zero-mean with variance uncorrelated for different
. The Channel frequency response
corresponding to the mth
transmit and the nth
receive antenna
for the o th
tone at time r is
The vector form representation of the Multi-carrier system
relation shown in (1) can be expressed as
(2)
Where
(3)
Multiple power levels are owed to the transmitting signals
to transmit over the channel. The effective utilization of
resources is due to the best possible utilization of
transmitting power. To achieve effective allocation of
resources a “resource allocation” approach has been
designed which has been outlined in the following section.
3. LOAD MATRIX [ 5] APPROACH
Load Matrix (LM) approach has the characteristic of jointly
supervising the interference within a cell while allocating
radio resources to users and to circumvent Rise over thermal
noise (RoT) outage by taking into consideration the inter
cell interference information. The management of inter cell
interference is the main difficulty for resource allocation in
multi-cell system. LM is a centralized scheduler which
provides radio resources to all dynamic users in the network
by using a database containing the load part of all dynamic
users in the network.
The critical problem in the uplink scheduler is to assign
proper transmission rate and time to all dynamic users, to
result in utmost utilization of radio resources across the
network while rewarding the QoS necessities of all the
users. The significant issue in the resource allocation is the
users transmit power. The subsequent Limitations are to be
satisfied for a network of N users and M cells/base stations .
Limitation1: This states that for each dynamic user i in the
network the transmitted power must be in an acceptable
region defined as
(4)
Where is the maximum user power.
Limitation 2: A definite threshold level for all M base
stations must be maintained and the total received power at
base station must be kept below this threshold. In the
network RoT can be used to be a sign of the interference
constraints.
(5)
Where is the total band received power, preset target
value to maintain uplink interference level at the base station
o (BSo ) over thermal noise. For a network containing M
dynamic users the of cells can be estimated by using
, which can be written as
(6)
Limitation 3 :The signal to noise plus interference ratio
necessary at the oth
serving base station if rate ‘p’ is being
assign to the user to attain a given frame error rate is
. For each user, depending on its channel
form and speed, each rate p has a least required called
. This constraint satisfies only by
considering as
(7)
LM is nothing except a centralized scheduler assigns radio
resources to all the N users and M cells in the network,
is the load factor contribution by user n at
defined as
(8)
Where is the channel gain from user n to BSo averaged
over scheduling period, is the thermal noise and un is the
transmitted power. The LM n,o values stored in column ‘o’
of LM database, RoT of cell ‘o’ can be written as
(9)
can be written as
(10)
The necessary transmitted power for user n at rate p is,
(11)
If above all Limitations are satisfied then only power is
acceptable and user n will be scheduled for transmission.
After that LM elements are updated and is calculated
for each cell using [10]. The performance of the LM
scheduling has the best RoT over other algorithms because
this scheduler significantly reduces the probability of the
RoT exceeding its target. The RoT is computed over a single
carrier system. The Load matrix approach considered in the
previous section is able to allocate the power efficiently for
a single cell users based on SNIR and RoT concepts,
considering only signal to noise ratio for power allocation
for single carrier communication.

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4. LM – BFSNIR APPROACH
In Multi-carrier communication system the Signal to
interference ratio is affected distinctly in each carrier hence
a single SNIR for allocation is not optimal. Also, since due
to usage of orthogonally modulated signals for transmission
over narrow band channels the interference between them is
decreased.
Hence SIR which is distinct in each channels is almost
maximized ,for the optimization of power allocation the
total SIR in Multi carrier system is sum of SIR’s in
individual channels which greater than the SNIR obtained in
single carrier system. This can be mathematically expressed
as
(12)
In equation (12), the SNIR used in single carrier systems is
bifurcated in terms of SNR and SIR
Where denotes the background signal-to-noise
ratio . SIR is the signal-to-interference ratio evaluated for in
every narrow channel by doing so the (12) can be rewritten
as shown
(13)
Where BFSNIR is called as bifurcated SNIR evaluated for
multi-carrier system designed with four transmit and receive
antennas(ie =4), substituting the above equation (13) for
the conventional LM approach, the proposed get
modified as
(14)
The required transmitted power for user i at rate p is then
defined as,
(15)
The allocable power to each user with rate p is then defined
as;
(16)
Else
user will be in queue and scheduled for transmission next
Transmission time interval(TTI)
5. SIMULATION RESULTS
For the simulation of the planned work a 3GPP-LTE
standard wireless communication model is taken. The
considered communication parameter for the evaluation is
given as in Table 1;
The proposed work is evaluated using MATLAB and the
simulated results are as follows
Table 1
S.No Parameter Description
1 Category 1
2 Uplink data
rate(UL-DR _peak )
5 Mbps
3 Down link data rate
(DL-DR _peak)
10Mbps(used
5mbps)
4 RF Bandwidth 20 MHz(CC)
5 Modulation Uplink-16 QAM
Downlink-
16QAM
6 Architecture Uplink-MIMO
4x4 (OFDM)
7 Channel condition Urban Micro
8 Channel Delay
Factor
1.627e-8sec
9 Channel Nature Additive
,Random

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Fig 1: Plot of orthogonally modulated signals used for transmission
The above figure shows the orthogonally modulated signals for transmission
Fig 2: SNIR vs BER plot for the multi Carrier system using LM coding
The figure above shows the variation of Bit Error Rate (BER) for different values of SNIR evaluated over multi carrier mobile
communication systems .

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Fig 3: SNIR vs BER plot for the multi Carrier system using LM-BFSNIR coding
The result outlines the obtained BER over variable SNIR at
different data rate.By observing the figures 2 and 3 it can be
seen that the BER decreases noticeably by using LM-BF
SNIR coding than the conventional LM coding . For
example for a SNIR of 13 db the BER decreases from 10-11
to 10-13
using LM-BFSNIR compared to LM coding .
6. CONCLUSION
In this paper, LM coding is evaluated for multi-carrier
mobile communication system . In past work Load matrix
approach is applied for single carrier system and the power
is allocated to the users by considering SNIR.By considering
the LM-BFSNIR approach in multi-carrier system it is
observed that the inter cellular interference is reduced better
than the single carrier systems and in turn reduces the bit
error rate .
REFERENCES
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Conference on Wireless Networks, Communication and
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[2]. J.H Winters “On the Capacity of radio communication
systems with diversity in a Rayleigh fading environment.
”IEEE J. Select. Areas Communication,vol.SA-5,pp 871-
878,june 1987.
[3]. G. J. Foschini, “Layered space–time architecture for
wireless communication in a fading environment when
using multi-element antennas,” Bell Labs Tech. J., pp. 41–
59, Autumn 1996.
[4]. G. J. Foschini, G. D. Golden, R. A. Valenzuela, and P.
W. Wolniansky, “Simplified processing for high spectral
efficiency wireless communication employing multi-
element arrays,” IEEE J. Select. Areas Communication., vol.
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[5]. Mohammad Abaii, Yajian Liu, and Rahim Tafazolli,
“An Efficient Resource Allocation Strategy forFuture
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Communications, Vol. 7, No. 8, August 2008.

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An approach to control inter cellular interference using load matrix in multi carrier mobile communication systems