Cognitive Radio Networks: Dynamic Resource Allocation Schemes

109 Pages·2014·6.83 MB·English

by  Shaowei Wang (auth.)

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Shaowei Wang
Cognitive Radio Networks
Dynamic Resource Allocation Schemes
1 3
Shaowei Wang
Nanjing University
Nanjing
Jiangsu
China
ISSN 2191-5768 ISSN 2191-5776 (electronic)
ISBN 978-3-319-08935-5 ISBN 978-3-319-08936-2 (eBook)
DOI 10.1007/978-3-319-08936-2
Springer Cham Heidelberg New York Dordrecht London
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To my parents, wife, daughters and sister, for
always being there for me.
Shaowei Wang
v
Preface
The current static spectrum management policies have caused a severe dilemma
of spectrum scarcity versus under-utilization. Accordingly, the emerging Cognitive
Radio (CR) technology, which allows dynamic spectrum access, has been widely
deemed as a promising candidate to improve the utilization of the precious natural
resource-radio spectrum for the next generation of wireless communication. Given
the space-time-frequency variation in wireless communication environment, dy-
namic resource allocation severs as a pivotal issue to achieve the high performance
of CR systems.
This brief is intended to provide a summary survey of different dynamic resource
allocation schemes in CR systems, with focuses on, particularly, the spectral-effi-
ciency and energy-efficiency in wireless communication networks. With a summary
introduction of the landscape of CR technology, we detail the dynamic resource
allocation problem for its motivation and challenges in CR systems. In terms of
preferences, the network operator may be inclined more toward Spectral-Efficien-
cy (SE) or Energy-Efficiency (EE) metrics in practical systems. Accordingly, the
Spectral- and Energy-Efficient resource allocation schemes are comprehensively
investigated in this monograph, respectively. Besides, through extensive analysis,
we also explore the interrelationship between the SE and the EE, and further throw
new insights into the SE-EE trade-off for operating strategies. We hope that this
brief will be used as a reference for practicing engineer and researchers in the field
of wireless communications.
Nanjing 210023, China Shaowei Wang
vii
Contents
1 Introduction ................................................................................................ 1
1.1 Cognitive Radio Technology ............................................................... 1
1.1.1 Cognitive Radio Characteristics .............................................. 1
1.1.2 Cognitive Radio Functions ...................................................... 2
1.1.3 Interference Temperature ........................................................ 4
1.2 OFDM Technology ............................................................................. 4
1.2.1 Key Features............................................................................ 4
1.2.2 OFDM-Based CR Systems ..................................................... 5
1.2.3 Summary ................................................................................. 6
References .................................................................................................... 7
2 Dynamic Resource Allocation ................................................................... 9
2.1 Resource Allocation in OFDM Systems ............................................. 9
2.1.1 Wireless Channel Characteristics ............................................ 9
2.1.2 FFT-Based Transceiver ........................................................... 10
2.1.3 Efficiency and Fairness ........................................................... 13
2.1.4 Classes of Dynamic Resource Allocation ............................... 14
2.1.5 General Problem of RA in Multiuser OFDM Systems ........... 14
2.2 Resource Allocation in CR Systems ................................................... 17
2.2.1 Primary/Secondary Network Models ...................................... 17
2.2.2 CR Operation Models ............................................................. 18
2.2.3 Interference Management ........................................................ 19
2.2.4 General Problem of RA in OFDM-Based CR Systems .......... 20
2.3 Summary ............................................................................................. 22
References .................................................................................................... 22
3 Spectral-Efficient Resource Allocation in CR Systems .......................... 27
3.1 Single-User CR Systems ..................................................................... 27
3.1.1 System Model.......................................................................... 27
3.1.2 Problem Formulation .............................................................. 29
3.1.3 Fast Barrier Algorithm ............................................................ 29
3.1.4 Numerical Results ................................................................... 33
ix
x Contents
3.2 Multi-User CR Systems ...................................................................... 35
3.2.1 System Model & Problem Formulation .................................. 35
3.2.2 Relaxation Method .................................................................. 37
3.2.3 Two-Stage Method .................................................................. 41
3.2.4 Numerical Results ................................................................... 45
3.3 Relay-Enhanced CR Systems .............................................................. 48
3.3.1 Three-Node Relay System ...................................................... 49
3.3.2 Multiuser Relaying CR Systems ............................................. 52
3.3.3 Numerical Results ................................................................... 59
3.4 Summary ............................................................................................. 64
References .................................................................................................... 64
4 Energy-Efficient Resource Allocation in CR Systems ............................ 67
4.1 EE Characteristics ............................................................................... 67
4.2 Energy-Efficient Power Allocation ..................................................... 71
4.2.1 General Problem...................................................................... 71
4.2.2 Bisection-Based Algorithm ..................................................... 72
4.2.3 Fractional Programming.......................................................... 74
4.2.4 Hypograph-Based Algorithm .................................................. 75
4.2.5 Performance Evaluation .......................................................... 76
4.3 Multiuser CR Systems......................................................................... 78
4.3.1 Problem Formulation .............................................................. 79
4.3.2 Relaxation Method .................................................................. 80
4.3.3 Numerical Results ................................................................... 86
4.4 Summary ............................................................................................. 89
References .................................................................................................... 91
5 Trade-Off Between Spectral- and Energy-Efficiency ............................. 93
5.1 SE-EE Relationship ............................................................................. 93
5.2 SE-EE Trade-off Operation ................................................................. 98
5.2.1 Pareto Optimal Set .................................................................. 98
5.2.2 Analysis of Utility Function .................................................... 99
5.2.3 D.C. Programming .................................................................. 99
5.2.4 Numerical Results ................................................................... 101
5.3 Summary and Discussions .................................................................. 102
References .................................................................................................... 103
Chapter 1
Introduction
Built on a software-defined radio, cognitive radio (CR) [1, 2] is generally defined as
an intelligent wireless communication paradigm with the awareness of its environ-
ment, which is able to learn from the environment and adapt to statistical variations
in the input stimuli using understanding-by-building methodology. It is proposed to
achieve efficient radio spectrum utilization, as well as high reliable communication
whenever and wherever needed.
1.1 Cognitive Radio Technology
CR technology allows secondary users (SUs), also referred to as CR users, to sense
the radio environment and access the radio spectrum licensed by primary users
(PUs), as long as the SUs do not worsen the performance of the PUs. In order
to meet the requirements of opportunistic access, the physical layer of a CR sys-
tem should be very flexible, which necessitates multicarrier methods to operate in
CR networks. Orthogonal frequency division multiplexing (OFDM), which offers
a high flexibility in radio resource management, is deemed as an appropriate air
interface of a CR system [3, 4].
1.1.1 Cognitive Radio Characteristics
With the staggering increase of new wireless applications, the last decade has wit-
nessed the looming exhaustion of radio spectrum. On the other hand, the traditional
spectrum management policy, which generally assigns the radio spectrum in a fixed
manner, becomes a bottleneck for high efficient spectrum utilization. As disclosed
by the report of Federal Communication Commission (FCC), the temporal and
geographic variations in the utilization of the licensed spectrum range from 15 to
85 % [5], as illustrated in Fig. 1.1. Consequently, such dilemma starves for innovative
© The Author(s) 2014 1
S. Wang, Cognitive Radio Networks, SpringerBriefs in Computer Science,
DOI 10.1007/978-3-319-08936-2_1