Project proposal on electronic

1. Inter-cell Interference Mitigation
in LTE Network
Prepared by: BURHAN OMAR SHEIKH AHMED (ME111017)
Supervised by: ASSOC.PROF. DR. SHARIFA KAMILAH BT SYED YUSOF
FACULTY OF ENGINEERING
RESEARCH PROJECT PROPOSAL (MEL1813)
02/05/2012

2. 2
Contents
Introduction
Problem Statement.
Objectives.
scope of work.
Background and Literature Review
Methodology.
Preliminary Results.
Project schedule
Conclusion
References.

3. 3
 Problem Statement.
 Objectives.
 Scope of work
Part I - Introduction

4. 4
 Due to lots of technological changes and market
oriented demands, mobile communication
technology is moving into next generation.
 Due to increasing demands for higher data rates and
higher capacities.
 Due to the limited amount of radio resources,
Frequency Reuse Scheme become a better option.
Introduction

5. 6
OFDM Based Systems (LTE)
Suffer
INTER-CELL
INTERFERENCE
INTRA-CELL
INTERFERENCE
 Intra-cell Interference is originated
by every other user transmitting in the
same cell.
 Orthogonality of the sub-carriers
effectively eliminate the Intra-cell
Interference.
 Inter-cell Interference is caused by
all concurrent users in neighboring cells
or sectors.
 Co-frequency sub-carriers are
reused among different cells.

6. 7
UE 2
eNB 2
Cell 2
eNB 1
Cell 1
UE 1

7. 8
Problem Statement
In OFDMA-based networks (LTE)
1. Universal Frequency Reuse which is to improve the system
throughput by using same frequency resource with another
neighbor cell will experience larger inter-cell interference,
especially at the cell boundary.
2. Due to the need for a high capacity per unit area which causes
the sector sizes to be small. This will lead interference to
occur.
How to mitigate Inter-cell Interference and improve
cell edge performances Is the most issue facing
OFDM based networks
?

8. 9
Objectives
The objectives of this work are:
1. To investigate Inter-cell Interference in multicell environment.
2. To mitigate interference using IDMA based system.
3. To develop hybrid SC-FDMA-IDMA system.
4. To evaluate the performance of hybrid SC-FDMA-IDMA in
multicell environment.

9. 10
Scope of Work
The scope of this work is:-
 Study Inter-cell Interference mitigation in multicell environment
based on Interleave Division Multiple Access (IDMA).
 LTE Uplink transmission (SC-FDMA).
 Evaluate the Performance of Hybrid Scheme SC-FDMA-IDMA
based on PAPR, BER and Throughput
 In simulation MATLAB tools will be used.

10. 11
Part II: Literature Review
Background and Literature Review
Interference Mitigation Techniques.
Interleave-Division Multiple-Access (IDMA)
Scheme .
Single Carrier Frequency Division Multiple
Access (SC-FDMA).

11. 12
Interference Mitigation Techniques
 A variety of Inter-cell interference mitigation
techniques have been proposed for OFDM
networks, including [1][9]:
Interference Mitigation
Techniques
Interference
Randomization
Interference
Coordination
Interference
Cancellation

12. 13
Scheme Example Advantages Disadvantages
3GPP TSG RAN WG1 , R1-050608, RITT, . Inter-cell Interference Mitigation based on IDMA.
France, 20 - 21 June, 2005
Interference
Randomization
•Cell-Specific
Interleaving (IDMA)
•Frequency Hopping.
•No additional
measurements and
signaling are needed
•UE must have
knowledge of the
channel coding and
modulation applied to
the interfering signal
3GPP TSG RAN WG1 #41, R1-050406. OFDM-based physical layer for the DL: inter-cell
interference avoidance /cancellation/estimation. Alcatel. France Telecom and Orange. May 9th–
13th, 2005
Interference
Cancellation
•Successive Interference
Cancellation.
•Parallel Interference
Cancellation.
•partially reduce the
interference level.
•heavy complexity
overhead and only
limited amount of
strong interferences
can be cancelled
Inter-cell Interference Mitigation Schemes

13. 14
Scheme Example Advantages Disadvantages
X. Zhang, Chen He, L. Jiang, Jing Xu. Inter-cell Interference Coordination Based on
Softer Frequency Reuse in OFDMA Cellular Systems. IEEE Int. Conference Neural
Networks & Signal Processing. Zhenjiang, China. June 8-10,2008.
Interference
Coordination
•Fractional
Frequency Reuse
(FFR)
•Soft Frequency
Reuse (SFR)
•the spectrum in
each sector remain
Constant and can
be done off-line via
network planning.
•cell-edge user can use
part of frequency band
•spectral efficiency
drop due to larger reuse
factor (such as 3) at
cell edge
Inter-cell Interference Mitigation Schemes (Cont..)

14. 15
IDMA scheme is a technique
that relies on interleaving as
only means for user separation .
IDMA inherits many advantages
from CDMA:-
diversity against fading and
mitigation of the worst-case cell
edge problems.
simple chip-by-chip iterative
MUD strategy [3].
Fig (1) : IDMA Transmitter and Receiver structures [3]
Interleave-Division Multiple-Access (IDMA)
Scheme

15. 16
IDMA in Uplink/Downlink
IDMA in the Downlink case
UE1 served by NodeB1 with
interleaving pattern1
 UE2 served by NodeB2 with
interleaving pattern2
IDMA in the Uplink case:
UE1 and UE2 interleave
their signals with distinct
interleaving patterns
Fig (2). Using IDMA in downlink to
suppress inter-cell interference
Fig (3). Using IDMA in uplink to suppress inter-cell interference

16. 17
IDMA Transmitter
• the coded sequence is permuted by
an interleaver πk.
The key principle of IDMA is:
1. Interleavers should be different
for different users.
2. Interleavers are generated
independently and randomly [3].
• The input data sequence dk of user k is encoded based on low-rate
code C.
Fig (4) : IDMA Transmitter structures [3]

17. 18
 IDMA receiver consist of :-
1. Elementary Signal
Estimator (ESE).
2. single-user a posteriori
probability (APP) decoders
(DECs).
 The outputs of the ESE and
DECs are extrinsic log-
likelihood ratios (LLRs) about
Xk(j) [4]:-
IDMA Receiver Structure
Fig (5) : IDMA Receiver structures [3]

18. 19
.
Feed the ESE LLR output to the decoder.
Calculate the total mean and variance of the received signal.
generate the ESE LLR value for the de-interleaved chip using the LLR
equation.
ESE operation
Despread the output of ESE
Produce the Extrinsic LLR for each chip
DEC operation
Update the statistics and then re-interleave
Use the updated statistics to refine the interference
mean and variance for the next iteration.

19. 20
 Single Carrier Frequency Division Multiple Access (SC-
FDMA) is Uplink Scheme for LTE
1. Low Peak-to-Average Power Ratio (PAPR) of the transmitted
waveform.
2. It has ability to remove ISI (Inter Symbol Interference).
3. Less sensitivity to carrier frequency offset.
4. SC-FDMA has very complicated frequency domain
equalizer.
SC-FDMA

20. 21
 This figure below shows the Transmitter and receiver
structure of SC-FDMA and OFDMA systems [5].
SC-FDMA
Fig(6): Transmitter and receiver structure of SC-FDMA

21. 22
Hybrid Scheme SC-FDMA-IDMA
Fig (9) : Uplink transmitter and receiver structures of SC-FDMA-IDMA
This is the uplink transmitter and receiver structure for the hybrid
system between SC-FDMA and IDMA technique [6]

22. 23
 Jing Lin et al, showed that Inter-cell interference (ICI) is a major
performance limiting factor in cellular OFDM system such as LTE.
 they proposed a methodology that groups the interfering BS into
strong-interfering BS (S-BS) and weak-interfering BS (W-BS).
1. The interfering signals from W-BS they considered as Gaussian
noise.
2. The interfering signals from S-BS are simultaneously detected
and suppressed based on the principles of the IDMA scheme [7].
Literature Review of IDMA

23. 24
 The figure below shows the BER performance with several numbers of S-
BS. From the graph they showed that the proposed algorithm works if the
strong base station is less than 5 S-BSs, which seems applicable for practical
system [7].
Fig (10): BER performance with different number of S-BSs (7 iteration)
Literature Review of IDMA

24. 25
 Xiong et al, proposed a hybrid multiple access technique for
LTE uplink, they combined SC-FDMA and IDMA for better
performance.
 SC-FDMA-IDMA performs better performance than OFDM-
IDMA in PAPR for LTE uplink, where in BER performance is
close to each other [6].
 The Hybrid Scheme has good features:-
Low Peak Average Power Ratio
(PAPR )
SC-FDMA
Simple and Effective Iteration MUD
IDMA

25. 26
Part III: Methodology

26. 27
Phase 1
Phase 2
Phase 3
Project Initiation & Planning
Study the Concept of Inter-cell Interference Mitigation
Techniques in Multicell environment
Evaluate the performance of IDMA based system
Apply IDMA concept in LTE Uplink Transmission
Analyze and evaluate the performance of the Hybrid
SC-FDMA-IDMA using Matlab Simulation
Report Writing

27. 28
 PAPR simulations for SCFDMA with comparison to
PAPR for OFDMA is done in this preliminary result
Preliminary Result
System bandwidth 5 MHz
Data modulation format QPSK
Number of total subcarriers 512
SC-FDMA input block size 128 symbols
Number of iterations > 104
Simulation parameters

28. 29
Preliminary Result
•This is the Transmitter side of SC-FDMA.
•To determine the PAPR we will consider only the Transmitter part.

29. 30
Uplink Transmission Scenario:
Preliminary Result
Data block generation
(size = M)
M-point FFT
Subcarrier mapping
512-point IFFT
Up-sampling
Pulse shape filtering
PAPR calculation
Block diagram of PAPR simulator for SC-FDMA

30. 31
Comparison of CCDF of PAPR for IFDMA, DFDMA, LFDMA, and OFDMA with total
number of subcarriers N = 512, number of input symbols M = 128, IFDMA spreading
factor Q = 4, DFDMA spreading factor ˜Q = 2, and α (roll-off factor) = 0.22 and QPSK
Preliminary Result

31. 32
Comparison of CCDF of PAPR for IFDMA and LFDMA with total
number of subcarriers N = 256, number of input symbols M = 64, spreading
factor
Q = 4, and α (roll-off factor) of 0, 0.2, 0.4, 0.6, 0.8, and 1 . QPSK
Preliminary Result
The figure below shows the impact of the roll-off factor α on the
PAPR when using raised-cosine pulse shaping

32. 33
Project schedule
Description/Weak 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Literature Review
Project Synopsis Submission
Preparation of Seminar Material
Seminar Material Submission
Simulation of preliminary design and
result
Preparation for Seminar
Seminar Presentation
Report Writing
Report Submission

33. 34
1. Theoretical and concept of interference mitigation techniques
have been concerned.
2. Most challenging problem in OFDM based system is the inter-
cell interference.
3. IDMA could provide an effective way in suppressing the inter-
cell interference and improving the “cell edge” performance.
4. Especially IDMA can be used for cell edge improvement where
the other types of interference mitigations have limited
throughput.

34. 35
1. Yong Soo Cho, Jaekwon Kim, Won Young Yang and Chung G. Kang. MIMO-OFDM
wireless communications with MATLAB. Singapore. John Wiley & Sons.2010.
2. Weiwei Wu. Performance Evaluation of Inter-cell Interference Mitigation Techniques for
OFDMA Cellular Networks. Ph.D. Thesis. University of Melbourne. 2010.
3. Li Ping, L.Liu, K. Y .Wu, and W. K. Leung. Interleaved-division multiple-access. IEEE
Trans.Wireless Commun. Vol. 5,.no 4. Apr. 2006，pp.938-947.
4. Zongyan Li, Luying Li, Zhanji Wu and Wenbo Wang.Uplink Transmission Techniques for
Interleave-Division Mulitple-Acess on block fading channel. 2010
5. Hyung G. Myung and David J. Goodman. Single Carrier FDMA - A New Air Interface For
Long Term Evolution. USA. John Wiley & Sons2008.
6. XINGZHONG, X. & ZHONGQIANG, L. Year. SC-FDMA-IDMA: A Hybrid Multiple
Access Scheme for LTE Uplink. In: Wireless Communications, Networking and Mobile
Computing (WiCOM), 2011 7th International Conference on, 23-25 Sept. 2011 2011. 1-5.
7. JING, L., FANGJIONG, C. & BENSHENG, C. Interleave-division-multiple-access based
intercell interference cancellation for cellular OFDM system. In: Machine Learning and
Cybernetics (ICMLC), 2011 International Conference on, 10-13 July 2011 2011. 1395-1398.

35. 36
8. Farooq Khan. LTE for 4G Mobile Broadband Air Interface Technologies and Performance.
New York. Cambridge University Press. 2009.
9. Xunyong Zhang, Chen He, Lingge Jiang, Jing Xu. Inter-cell Interference Coordination Based
on Softer Frequency Reuse in OFDMA Cellular Systems. IEEE Int. Conference Neural
Networks & Signal Processing. Zhenjiang, China. June 8-10,2008.
10. 3GPP TSG RAN WG1 , R1-050608, RITT, . Inter-cell Interference Mitigation based on
IDMA. France, 20 - 21 June, 2005

36. 37
Thank you

37. 38
Formulas
Appendix

38. 39
Elementary Signal Estimator (ESE) cont.
Algorithm : Chip-by-Chip Detection [3]
 Step (I): Estimation of Interference Mean and Variance
Mean and Variance
for Received signal
Mean and Variance for the distortion (including interference-plus noise)
 Step (II): LLR Generation
Soft information
exchanged between the
receiver components.

39. 40
Single-user (APP) decoders (DECs).
 The DECs carry out APP decoding using the output
of the ESE as the input.
 DECs output is the extrinsic LLRs of {Xk(j)}:-
 Mean and Variance:-
 Mean and the Variance will be used in the ESE to update the
interference mean and variance in the next iteration [3].