40120140503008

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 –
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp. 51-57 © IAEME
51
LTE – INTER-CELL INTERFERENCE MANAGEMENT TO IMPROVE THE
QUALITY RECEPTION IN DOWNLINK RADIO RESOURCES LINKS
Younes BALBOUL, Fatiha MRABTI, Najiba EL AMRANI EL IDRISSI,
Signals, Systems and Components Lab.
Faculty of Science and Technology, Fez, Morocco
ABSTRACT
LTE (long term evolution) target a high bit rate and QoS (Quality of Service) but is hampered
by the significant increase of the number of users. The cellular concept enabled to expand the service
coverage to an unlimited large area by dividing the service area into multiple cells with a BS
deployed in each cell and reusing the given frequency spectrum repeatedly in each cell. This,
however, brings in the co-channel interference problem among the neighboring cells and hence the
cellular concept can truly achieve its goal only when the inter-cell interference is properly resolved.
The inter-cell resource management refers to a collection of operations that intend to achieve a
maximized QoS by minimizing the performance degradation caused by the inter-cell interference.
In this work, to improve the downlink radio link, we will use, Partial Frequency Reuse with LP-
OFDM modulation in the inner-cell and in the cell-edge we will use Partial Frequency Reuse and
OFDM modulation supported by the coordination with adjacent cells. Matlab simulation of different
scenarios showed an improvement in bit error rate at the receiver. The results are processed
according to the Monte Carlo criteria.
I. INTRODUCTION
The choice of an appropriate modulation, OFDM (Orthogonal frequency division
multiplexing), and multiple-access technique (MIMO Multi Input Multi Output) for mobile wireless
data communications is very important to achieve good system performance.
OFDM has been considered as a promising modulation technique for the future generation
wireless systems, such as Wimax (Worldwide Interoperability for Microwave Access) and LTE. Not
only for its inherent ability to combat inter-symbol interference (ISI) resulting from frequency
selective fading, but also for the flexibility it offers in radio resource allocations, as each subcarrier
can be modulated adaptively to exploit frequency-domain diversity and improve achievable data rates
on available frequency spectrum. However, in designing practical networks, optimization should be
performed in a multi-cell environment considering one of the most performance limiting factors,
namely inter cell interference (ICI) [1], [2].
INTERNATIONAL JOURNAL OF ELECTRONICS AND
COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)
ISSN 0976 – 6464(Print)
ISSN 0976 – 6472(Online)
Volume 5, Issue 3, March (2014), pp. 51-57
© IAEME: www.iaeme.com/ijecet.asp
Journal Impact Factor (2014): 7.2836 (Calculated by GISI)
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IJECET
© I A E M E

52
The market Trends (like a multicast services, streaming …), require some radio access
networks able to carry more and more data with stringent requirements in terms of QoS (minimum bit
rate, delay, etc.) The solution is to move to the reuse of bandwidth, but this technique is limited by the
inter cell interference (ICI) problem.
In this paper, the goal is to improve the quality of the down-link radio transmission. To do it we will
proceed along two scenarios:
• To improve the inner-cell down-link radio transmission we will use the Partial Frequency Reuse and
LP-OFDM modulation (Linearly Precoded Orthogonal Frequency Division Multi-plexing).
• To improve the cell-edge down-link radio transmission, we will also use the Partial Frequency
Reuse and the OFDM modulation with the coordination of adjacent cells.
The Matlab simulation of these scenarios showed an improvement in bit error rate at the
receiver. The results are processed according to the Monte Carlo criteria.
II. THE PROBLEM OF INTER-CELL INTERFERENCE IN DOWN LINK L.T.E
One limiting aspect for system throughput performance in cellular networks is the inter-cell
interference, especially for cell-edge users.
The impact of interference on the achievable data rate for a given user can be expressed
analytically. If a user k is experiencing no interference, then its achievable rate in an RB (Resource
Block) m of sub frame f can be expressed as:
D୩,୬୭ି୧୬୲ୣ୰୤ୣ୰ୣ୬ୡୣ ൌ
B
M
log ቈ1 ൅
Pୱሺm, fሻ|H୩
ୱ
ሺm, fሻ|ଶ
N଴
቉
Where M is the number of resources allocated in the band B, and H୩
ୱ
ሺm, fሻthe gain of the
channel of thecell s that serves the user k, P (m, f) is the transmission power of the cell sand N0 is the
noise power.
Figure 1. Example of inter-cell interference with two cells
If the neighboring cells to the cell s emit, then it is likely that the same resources are used, and hence
the achievable rate for user k is reduced to:
D୩,୵୧୲୦ ୧୬୲ୣ୰୤ୣ୰ୣ୬ୡୣ ൌ
B
M
log ቈ1 ൅
Pୱሺm, fሻ|H୩
ୱ
ሺm, fሻ|ଶ
N଴ ൅ ∑ P୧ሺm, fሻ|H୩
୧
ሺm, fሻ|ଶ
୧ ஷୱ
቉

53
With ∑ P୧ሺm, fሻ|H୩
୧
ሺm, fሻ|ଶ
୧ ஷୱ isthe sum of the interference and the index i represent the interfering
cells.
The loss of throughput due to interference experienced by user k is:
D୩,୪୭ୱୱ ൌ D୩,୬୭ି୧୬୲ୣ୰୤ୣ୰ୣ୬ୡୣ െ D୩,୵୧୲୦ ୧୬୲ୣ୰୤ୣ୰ୣ୬ୡୣ
D୩,୪୭ୱୱ ൌ
B
M
log ቎
1 ൅ SNR
1 ൅ ቂ
ଵ
ୗ୒ୖ
൅ γቃ
ିଵ቏
WithSNR ൌ
୔౩ሺ୫,୤ሻ|ୌౡ
౩
ሺ୫,୤ሻ|మ
୒బ
is the signal to noise ratio at the receiver input, and
γ ൌ
∑ ୔౟ሺ୫,୤ሻ|ୌౡ
౟
ሺ୫,୤ሻ|మ
౟ ಯ౩
୔౩ሺ୫,୤ሻ|ୌౡ
౩
ሺ୫,୤ሻ|మ
ൌ
୔౟౤౪౛౨౜౛౨౛౤ౙ౛
୔౫౩౛౨ ౡ
.
Figure 2 shows the rate loss for the user k due to the variation of the coefficient α ൌ 10logଵ଴ሺγሻ at
SNR = 0 dB.
Figure 2. The rate loss due to inter-cell interference
In the LTE broadband (reuse factor is 1), the rate of loss of data at the inner-cell will be
greater than 8% and less than 40% and in the cell-edge, it is greater than 40% and 90% (Figure 2).
This is unacceptable in a system that must ensure high throughput [3].
The current challenge is to develop a system that reduce the effect of inter-cell
interference by the use of a suitable cell pattern, more flexible frequency reuse techniques and Semi-
static inter-cell interference coordination allowing improved radio transmission experience.
In the next part of this paper we will introduce our contribution which present the main aspects of a
new technique for managing inter cell interference. This technique is based on Partial Frequency
Reuse, semi-static coordination techniques and the pre-coding process wish implement space
diversity and frequency. All these new techniques allow improving the quality of service for all users
(whether inner-cell or cell-edge users).

International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976
6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp.
III. IMPROVING RADIO TRANSMISSION
To improve radio transmission experience in downlink our work is based on
Frequency Reuse (Figure 3) with round robin algorithm scheduling, coupled with two radio
transmission techniques namely: LP-
physical resources block (PRB) from different adjacent base stations in cell
Figure 3.
Figure
A. Algorithm concept
In the proposed algorithm, the treatment of inter
areas according to the value of SINR (Signal
receivers.
1) the inner-cell area with SINR greater than or equal to 2
- OFDM) is used,
6472(Online), Volume 5, Issue 3, March (2014), pp. 51-57 © IAEME
TRANSMISSION EXPERIENCE IN DOWNLINK
To improve radio transmission experience in downlink our work is based on
with round robin algorithm scheduling, coupled with two radio
-OFDM in inner-cell and the simultaneous transmission of several
physical resources block (PRB) from different adjacent base stations in cell-edge (Figure
Figure 3. Partial Frequency Reuse.
Figure 4. managing inter-cell interference.
he proposed algorithm, the treatment of inter-cell interference for a cell is separate in two
areas according to the value of SINR (Signal to Interference plus Noise Ratio) received at the user
with SINR greater than or equal to 2dB, the LP-OFDM (Linear Precoding
© IAEME
To improve radio transmission experience in downlink our work is based on the Partial
with round robin algorithm scheduling, coupled with two radio
cell and the simultaneous transmission of several
(Figure 4).
cell interference for a cell is separate in two
to Interference plus Noise Ratio) received at the user
OFDM (Linear Precoding

55
2) In the cell-edge area with SINR strictly lower to 2 dB, two or three PRB with OFDM
modulation from different adjacent cells are allocated to the user. Figure 5 gives an overview of this
new technique.
Figure 5. Operating principle
B. Inner-cell : LP-OFDM Technique
In this paper we use the results of a research that was conducted by IEEE for LP-OFDM
modulation technique and uses these results in the context of LTE system. This research proposes an
iterative receiver for the LP-OFDM with channel coding. This gives very good results in terms of
BER at a very low cost of complexity. In fact, the proposed iterative receiver requires no matrix
inversion and its complexity do not increase with linear precoding, and with the modulation order.
Inter symbol interference created by linear precoding are effectively removed in the iterative "turbo
effect"[4].
Figure 6. The BER performance of the LP-OFDM with iterative receiver and coding rate ½.

6464(Print), ISSN 0976 – 6472(Online), Volume 5, Issue 3, March (2014), pp.
LP-OFDM with iterative receiver provides better results than the OFDM for SNR more than 2
dB, which justifies the use of this technique for the inner
C. Cell-edge : multi-cell coordination
The technique used in cell
Indeed, for the downlink access, a user at the cell
adjacent cells. These resources have the same modulation symbol 4
Modulation), the same channel coding and carry the same information. The receiver combines these
resources using the MRC (Maximum Ratio Combining
therefore the best channel profile. This will allow to the user to extract the best signal from these
resources. The Figure 8 presents the Matlab results simulation of the transmission scenario
7.
Figure 7. Physical allocation resource scenario for a user at the cell
Figure 8. Simulation of BER versus SNR for 2 and 3 RB with use of MRC at the receiver.
6472(Online), Volume 5, Issue 3, March (2014), pp. 51-57 © IAEME
OFDM with iterative receiver provides better results than the OFDM for SNR more than 2
this technique for the inner-cell where the SNR meets this condition.
cell coordination
The technique used in cell-edge is based on collaboration between adjacent e
Indeed, for the downlink access, a user at the cell-edge receives 2 or 3 different PRB from different
adjacent cells. These resources have the same modulation symbol 4-QAM (Quadrature Amplitude
um Ratio Combining): extract the carrier of maximum power and
presents the Matlab results simulation of the transmission scenario
hysical allocation resource scenario for a user at the cell-edge.
Simulation of BER versus SNR for 2 and 3 RB with use of MRC at the receiver.
© IAEME
OFDM with iterative receiver provides better results than the OFDM for SNR more than 2
cell where the SNR meets this condition.
edge is based on collaboration between adjacent e-Node B.
2 or 3 different PRB from different
QAM (Quadrature Amplitude
extract the carrier of maximum power and
presents the Matlab results simulation of the transmission scenario in Figure
edge.
Simulation of BER versus SNR for 2 and 3 RB with use of MRC at the receiver.

57
In this simulation, it is clear that combining multiple physical resources, can significantly
improve the transmission conditions for the users at the cell-edge with a gain of 3 dB with 2 PRB
and a gain greater than 6 dB with three PRB allocations.
IV. CONCLUSION
A variety of resource scheduling algorithms may be applied by the eNode-B depending on
the optimization criteria required. In this paper we focused on the benefits of applying our technique
in the LTE systems, in terms of Quality of service enhancement. Our results reveal that the Partial
Frequency Reuse scheme with LP-OFDM in inner-cell provides a gain greater than 2 dB for SNR
(Signal to Noise Ratio) higher than 3 dB and inter-cell coordination at cell-edge, can significantly
improve the transmission conditions with a gain of 3 dB with 2 PRB (physical resource block) and a
gain greater than 6 dB with 3 PRB allocations. An overall scheme that implement the algorithm
suggested in a system which simulates realistic inter-cell interference complies with the 3GPP
specifications and compare it with the algorithms used in LTE will be the subject of our future
research.
REFERENCES
[1] « Soft Frequency Reuse Scheme for UTRAN LTE » 3GPP TSG RAN WG1 Meeting 41, Athens,
Greece, 9 – 13 Mai, 2005.
[2] Abdul Basit SYED,“Dimensioning of LTE Network. Description of Models and Tools, Coverage
and Capacity Estimation of 3GPP Long Term Evolution radio interface » à l’Université de
Technologie de Helsinki, Février 2009 à Espoo, Finland.
[3] Stefania SESIA, Issam TOUFIK et Matthew BAKER, “LTE – The UMTS Long Term
Evolution: From Theory to Practice”, John Wiley & Sons, Ltd, Second edition 2011.
P.-J. Bouvet, M. Hélard, , et V. Le Nir: « Low complexity iterative receiver for Linear Precoded
OFDM » Cesson-Sévigné, France. Wireless And Mobile Computing, Networking And
Communications, IEEE International Conference 2005.
[4] Asish B. Mathews and Dr. Pavan Kumar Yadav, “Suppression of Nonlinearity Induced
Distortions In Radio Over Fiber Links” International journal of Electronics and Communication
Engineering &Technology (IJECET), Volume 4, Issue 4, 2013, pp. 51 - 60, ISSN Print: 0976-
6464, ISSN Online: 0976 –6472.
[5] V. Bapuji, R. Naveen Kumar, Dr. A. Govardhan, Prof. S.S.V.N. Sarma, “Maximizing Lifespan of
Mobile Ad Hoc Networks With QOS Provision Routing Protocol” International journal of
Computer Engineering & Technology (IJCET), Volume 3, Issue 2, 2012, pp. 150 - 156, ISSN
Print: 0976 – 6367, ISSN Online: 0976 – 6375.

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