Interference Management and Call Admission Control in Two-Tier Cellular Wireless Networks by ...

125 Pages·2013·3.86 MB·English

Interference Management and Call Admission Control in Two-Tier
Cellular Wireless Networks
by
Nazmus Saquib
A Thesis submitted to the Faculty of Graduate Studies of
The University of Manitoba
in partial fulfilment of the requirements of the degree of
MASTER OF SCIENCE
Department of Electrical and Computer Engineering
University of Manitoba
Winnipeg
Copyright (cid:13)c 2013 by Nazmus Saquib
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Supervisor: Prof. Ekram Hossain
ABSTRACT
Two-tiermacrocell-femtocell network is considered an efficient solution toenhance
area spectral-efficiency, improve cell coverage and provide better quality-of-service
(QoS) to mobile users. However, interference and mobility management are consid-
ered to be the major issues for successful deployment of macrocell-femtocell network.
In this thesis, a unified framework is developed for interference management, resource
allocation, andcalladmissioncontrol(CAC)fortwo-tiermacrocell-femtocellnetwork.
Fractional frequency reuse (FFR) is considered to provide both link-level and call-
level QoS measures for mobile users. In this framework, joint resource allocation and
interference coordination problem is formulated as an optimization problem to obtain
designparametersforsectoredFFR.TheCACproblemisformulatedasSemi-Markov
Decision Process and Value Iteration Algorithm is used to obtain optimal admission
control policy. Performance of this framework is evaluated through simulations. The
performance evaluation results show that the proposed framework outperforms tra-
ditional non-optimized FFR scheme in two-tier network.
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Acknowledgement
First and foremost, I would like to express my utmost gratitude and deepest
appreciation to my advisor, Dr. Ekram Hossain, for his continual time, invaluable
guidance, encouragement, and research grants for the completion of the graduate
studies. It has been my honor and privilege to work under Dr. Hossain’s supervision.
Without his valuable support and help, it would not have been possible for me to
complete the thesis.
I would like to especially thank all the course instructors for their guidance and
support. Special thanks to the graduate student advisor of Electrical and Computer
Engineering department, and administrative staffs of the Faculty of Graduate Studies
for their valuable help throughout the graduate studies. I would like to acknowledge
the Manitoba Graduate Scholarship (MGS), awarded to me which was very inspiring
and influential in the development pursuit of my research.
I am extremely thankful to all the members of Wireless Communications, Net-
works, and Services Research Group for their continuous support and encouragement
from the start of the M. Sc. program till the completion of the thesis.
Last but not the least, I am ever grateful to my beloved parents and my sister for
their unconditional love, affection, support and sacrifices in every step of my life.
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This thesis is dedicated to my beloved parents.
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Table of Contents
Abstract ii
Acknowledgement iii
Dedication iv
Table of Contents v
List of Figures ix
List of Tables xii
1 Introduction 1
1.1 Overview of LTE Networks . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.1 The Core Network . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1.2 The Access Network . . . . . . . . . . . . . . . . . . . . . . . 4
1.1.3 The Air Interface . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1.4 Radio Base Stations in LTE . . . . . . . . . . . . . . . . . . . 6
1.1.5 Mobility Management . . . . . . . . . . . . . . . . . . . . . . 7
1.1.6 LTE-Advanced . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1.2 Heterogeneous Network (HetNet) . . . . . . . . . . . . . . . . . . . . 12
1.2.1 LTE Femtocells (HeNBs) . . . . . . . . . . . . . . . . . . . . 13
1.2.1.1 Access Network for HeNBs . . . . . . . . . . . . . . 14
1.2.1.2 Access Modes of HeNBs . . . . . . . . . . . . . . . . 15
1.2.1.3 Mobility Management . . . . . . . . . . . . . . . . . 15
1.3 Technical Challenges in Femtocell Deployment . . . . . . . . . . . . 16
1.3.1 Interference Management . . . . . . . . . . . . . . . . . . . . 16
1.3.2 Mobility management and handovers . . . . . . . . . . . . . . 17
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1.3.3 Timing and synchronization . . . . . . . . . . . . . . . . . . . 17
1.3.4 Security . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.3.5 Self-organization . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.4 Scope and Objective of the Thesis . . . . . . . . . . . . . . . . . . . 18
1.5 Contributions of the Thesis . . . . . . . . . . . . . . . . . . . . . . . 18
1.6 Organization of the Thesis . . . . . . . . . . . . . . . . . . . . . . . 20
2 Interference Management and Call Admission Control Femtocell
Networks: Issues and Approaches 21
2.1 Interference Management in OFDMA Femtocell Networks . . . . . . 22
2.1.1 Femto-aware Spectrum Arrangement Scheme . . . . . . . . . 24
2.1.2 Clustering of Femtocells . . . . . . . . . . . . . . . . . . . . . 25
2.1.3 Beam Subset Selection Strategy . . . . . . . . . . . . . . . . 27
2.1.4 Collaborative Frequency Scheduling . . . . . . . . . . . . . . 28
2.1.5 Power Control Approach . . . . . . . . . . . . . . . . . . . . 29
2.1.6 Fractional Frequency Reuse (FFR) and Resource Partitioning 30
2.1.7 Cognitive Approach . . . . . . . . . . . . . . . . . . . . . . . 33
2.1.8 Qualitative Comparison Among Different Interference Man-
agement Approaches . . . . . . . . . . . . . . . . . . . . . . . 34
2.2 Call Admission Control in OFDMA Femtocell Networks . . . . . . . 37
2.3 Motivation for the Proposed Framework . . . . . . . . . . . . . . . . 40
3 A Unified Framework for Interference Management and Call Admis-
sion Control for Two-tier HetNets with Static Fractional Frequency
Reuse 42
3.1 System Model and Assumptions: Inter-cell Interference Management,
Sub-channel Allocation, and Call Admission Control . . . . . . . . . . 45
3.1.1 Inter-cell Interference Management Based on Sectored FFR . 45
3.1.2 Selection of Sub-channels by HeNBs . . . . . . . . . . . . . . 46
3.1.3 Call Admission Control Model . . . . . . . . . . . . . . . . . 50
3.2 Channel Allocation for Sectored FFR: Problem Formulation and So-
lution Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
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3.2.1 Optimization for Channel Allocation and Interference Coordi-
nation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.2.2 Solution Methodology . . . . . . . . . . . . . . . . . . . . . . 55
3.3 Call Admission Control Policy for FFR-based HetNet . . . . . . . . 58
3.3.1 Problem Formulation . . . . . . . . . . . . . . . . . . . . . . 58
3.3.1.1 Decision Epochs . . . . . . . . . . . . . . . . . . . . 59
3.3.1.2 State Space . . . . . . . . . . . . . . . . . . . . . . . 59
3.3.1.3 Action Space . . . . . . . . . . . . . . . . . . . . . . 59
3.3.1.4 Expected Cost Value Function . . . . . . . . . . . . 60
3.3.1.5 State Transition Probabilities . . . . . . . . . . . . . 60
3.3.2 Optimal CAC Policy . . . . . . . . . . . . . . . . . . . . . . . 62
4 Performance Evaluation 67
4.1 Simulation Environment and Assumptions . . . . . . . . . . . . . . . 67
4.2 Simulation Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
4.2.1 Design Parameters for Sector-based FFR . . . . . . . . . . . 70
4.2.2 Optimal CAC Policy . . . . . . . . . . . . . . . . . . . . . . . 73
4.2.3 Call Blocking/Dropping Probability Performance . . . . . . . 73
4.2.4 Average Throughput Performance of UEs . . . . . . . . . . . 80
4.2.5 Effect of Minimum Rate Requirements on Blocking/Dropping
Probability Performance . . . . . . . . . . . . . . . . . . . . . 82
4.2.6 Effect of Variations in Link-level Transmission Power . . . . . 82
4.2.7 Comparison of Call-level QoS . . . . . . . . . . . . . . . . . . 86
4.3 Summary of the Observations . . . . . . . . . . . . . . . . . . . . . . 90
5 Summary and Future Work 91
5.1 Thesis Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
5.2 Future Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Bibliography 94
Appendix A 100
A.1 State Transition Probability . . . . . . . . . . . . . . . . . . . . . . . 100
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Appendix B 103
B.1 Proof of Monotonically Non-decreasing Property of Cost Function . . 103
Appendix C 108
C.1 Proof of Convexity of Cost Function . . . . . . . . . . . . . . . . . . 108
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List of Figures
Figure 1.1 A generic LTE cell architecture [3]. . . . . . . . . . . . . . . . 4
Figure 1.2 A generic diagram for intra-LTE mobility. . . . . . . . . . . . 8
Figure 1.3 Inter-MeNB mobility management via X2 interface. . . . . . . 10
Figure 1.4 Mobility management in a femtocell network. . . . . . . . . . 16
Figure 2.1 Interference scenarios in OFDMA-based femtocell networks. . 23
Figure 2.2 Femto-aware spectrum arrangement scheme [38]. . . . . . . . . 25
Figure 2.3 Sensing-based opportunistic power control [44]. . . . . . . . . 30
Figure 2.4 Interference management scheme using FFR [46]. . . . . . . . 32
Figure 2.5 Interference management through cognitive approach [48]. . . 34
Figure 3.1 Resource allocation and call admission control framework. . . 44
Figure 3.2 Switching boundary for MUEs. . . . . . . . . . . . . . . . . . 46
Figure 3.3 Sectored FFR scheme in HetNet: (a) FFR-3, (b) FFR-6. . . . 47
Figure 3.4 Arrival and departure of different call types in a sector for FFR-6. 51
Figure 4.1 Snap-shot of HeNB and UE locations for a two-tier HetNet. . 68
Figure 4.2 Cell throughput vs. fraction of center-zone radius (w.r.t. the
macrocell radius). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Figure 4.3 Cell throughput vs. fraction of total frequency spectrum allo-
cated to center-zone. . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
Figure 4.4 CAC policy for new femto call for normalized cost factor set-1:
arrival rate 0.3 calls/min for all call types. . . . . . . . . . . . . . . . 74
Figure 4.5 CAC policy for new femto call for normalized cost factor set-1:
arrival rate of macro-to-femto handover calls increased to 0.7 calls/min. 75
Figure 4.6 CAC policy for new femto call for normalized cost factor set-2:
arrival rate 0.3 calls/min for all call types. . . . . . . . . . . . . . . . 76
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Figure 4.7 CAC policy for new femto call for normalized cost factor set-2:
arrival rate of macro-to-femto handover calls increased to 0.7 calls/min. 77
Figure 4.8 New call blocking probability for normalized cost factor set-1. 77
Figure 4.9 Handoff call dropping probability for normalized cost factor set-1. 78
Figure 4.10 New call blocking probability for normalized cost factor set-2. 79
Figure 4.11 Handoff call dropping probability for normalized cost factor set-2. 79
Figure 4.12 Average throughput of MUEs for configuration 1 and 2. . . . . 81
Figure 4.13 Average throughput of FUEs for configuration 1 and 2. . . . . 81
Figure 4.14 New macro call blocking probability for normalized cost factor
set-1 as minimum rate requirement varies. . . . . . . . . . . . . . . . 83
Figure 4.15 Macro-to-macro handoff call dropping probability for normal-
ized cost factor set-1 as minimum rate requirement varies. . . . . . . 83
Figure 4.16 Femto-to-macro handoff call dropping probability for normal-
ized cost factor set-1 as minimum rate requirement varies. . . . . . . 84
Figure 4.17 New macro call blocking probability for normalized cost factor
set-1 as link-level transmission power varies. . . . . . . . . . . . . . . 84
Figure 4.18 Macro-to-macro handoff call dropping, probability for normal-
ized cost factor set-1 as link-level transmission power varies. . . . . . 85
Figure 4.19 Femto-to-macro handoff call dropping probability for normal-
ized cost factor set-1 as link-level transmission power varies. . . . . . 85
Figure 4.20 Comparison between the proposed model and the reference
model in terms of new macro call blocking probability for normalized
cost factor set-1 and target SNR at MUE = 15 dB. . . . . . . . . . . 87
Figure 4.21 Comparison between the proposed model and the reference
model in terms of macro-to-macro handoff call dropping probability
for normalized cost factor set-1 and target SNR at MUE = 15 dB. . . 87
Figure 4.22 Comparison between the proposed model and the reference
model in terms of femto-to-macro handoff call dropping probability
for normalized cost factor set-1 and target SNR at MUE = 15 dB. . . 88
Figure 4.23 Comparison between the proposed model and the reference
model in terms of new macro call blocking probability for normalized
cost factor set-1 and target SNR at MUE = 20 dB. . . . . . . . . . . 88