Radio Network Management in Cognitive LTE-Femtocell Systems
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Radio Network Management in Cognitive LTE-Femtocell Systems A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) Electronic and Computer Engineering School of Engineering and Design Brunel University United Kingdom By Saba Al-Rubaye January 2013 Abstract There is a strong uptake of femtocell deployment as small cell application platforms in the upcoming LTE networks. In such two-tier networks of LTE- femtocell base stations, a large portion of the assigned spectrum is used sporadically leading to underutilisation of valuable frequency resources. Novel spectrum access techniques are necessary to solve these current spectrum inefficiency problems. Therefore, spectrum management solutions should have the features to improve spectrum access in both temporal and spatial manner. Cognitive Radio (CR) with the Dynamic Spectrum Access (DSA) is considered to be the key technology in this research in order to increase the spectrum efficiency. This is an effective solution to allow a group of Secondary Users (SUs) to share the radio spectrum initially allocated to the Primary User (PUs) at no interference. The core aim of this thesis is to develop new cognitive LTE-femtocell systems that offer a 4G vision, to facilitate the radio network management in order to increase the network capacity and further improve spectrum access probabilities. In this thesis, a new spectrum management model for cognitive radio networks is considered to enable a seamless integration of multi-access technology with existing networks. This involves the design of efficient resource allocation algorithms that are able to respond to the rapid changes in the dynamic wireless environment and primary users activities. Throughout this thesis a variety of network upgraded functions are developed using application simulation scenarios. Therefore, the proposed algorithms, mechanisms, methods, and system models are not restricted in the considered networks, but rather have a wider applicability to be used in other technologies. This thesis mainly investigates three aspects of research issues relating to the efficient management of cognitive networks: First, novel spectrum resource management modules are proposed to maximise the spectrum access by rapidly detecting the available transmission opportunities. Secondly, a developed pilot power controlling algorithm is introduced to minimise the power consumption by considering mobile position and application requirements. Also, there is investigation on the impact of deploying different numbers of femtocell base stations in LTE domain to identify the optimum cell size for future networks. Finally, a novel call admission control mechanism for mobility management is proposed to support seamless handover between LTE and femtocell domains. This is performed by assigning high speed mobile users to the LTE system to avoid unnecessary handovers. The proposed solutions were examined by simulation and numerical analysis to show the strength of cognitive femtocell deployment for the required applications. The results show that the new system design based on cognitive radio configuration enable an efficient resource management in terms of spectrum allocation, adaptive pilot power control, and mobile handover. The proposed framework and algorithms offer a novel spectrum management for self- organised LTE-femtocell architecture. Eventually, this research shows that certain architectures fulfilling spectrum management requirements are implementable in practice and display good performance in dynamic wireless environments which recommends the consideration of CR systems in LTE and femtocell networks. i Acknowledgements All praise is to 'My God' for his grace, blessing, mercy and giving me the ability to complete this thesis. I'm feeling of his support toward me in each stage of my life. I would like to express my sincere gratitude to my supervisor professor 'John Cosmas' for his unflinching support, continuous motivation for quality work and encouragement. His support was vital to achieving this degree. His momentum and spontaneity has always restored an aura of research at the Wireless Network and Communication Centre (WNCC). I would like to acknowledge the encouraging and supportive attitude of all staff members at Brunel University for promoting research especially. All of them have been absolutely professional. Finally, my deepest gratitude goes to my husband 'Anwer' for his devotion, love, support, patience, and steady encouragement. I want to thank him from my heart for everything he has done. ii Declaration I hereby declare that the research documented in this thesis is my own unaided work, both in conception and execution. Information derived from the published and unpublished work of others has been acknowledged in the text and references are given in the list of sources. The thesis itself was composed and originated entirely by myself in the Wireless Networks and Communications Centre, Electronic and Computer Engineering Department, School of Engineering and Design at Brunel University. Copyright © by Saba Al-Rubaye 2013, London, UK iii Table of Contents Abstract ………………………………...……….………………….…………………. i Acknowledgements ………………………………..……………….…………………. ii Declaration…………………………………………………………………………….. iii Table of Contents …………………………………………………….………………. iv List of Figures …………………………..………..………………………..…………. viii List of Tables ………………………………..……….…………………….………….. xi List of Abbreviations…………………………….………………………………..….. xii List of Publications……………………………………………………………………. xv Chapter 1: Introduction ................................................................................... 1 1.1 Motivation ………………….................................................................................. .. 1 1.2 Problem Statement……………………………………………………………..….. 4 1.3 Aims of Research……………………………………………………….…………. 5 1.4 Methodology ……………………........................................................................... 6 1.5 Thesis Novel Contributions……………………………………………………….. 7 1.5.1 Novel Spectrum Resource Management Model………………………….…. 9 1.5.2 Spectrum Allocation Technique……………………………………….……. 10 1.5.3 New Power Management Approaches………………………………………. 10 1.5.4 Novel Mobility Management Mechanism…………………….…………….. 10 1.6 Thesis Organisation…………………………………………………….…..…….. 11 1.7 References…………………………………………………………………………. 13 Chapter 2: Background and Technical Challenges in Cognitive LTE Femtocell Systems ………….…….……… 15 2.1 Introduction …………………………….............................................................. 16 2.2 Current Standardisation ……….…..……………………………………………... 18 2.3 Long Term Evolution (LTE) Technology ………………………………………… 18 2.3.1 LTE-OFDM Technique………………………………………………………….. 19 2.4 Femtocell Networks……………………………………………………………..… 23 2.4.1 The Need for Small-Cell Base Station………………………………….…… 24 2.4.2 Femtocell Deployment Aspects………………………………………….….. 26 2.4.3 Access Mechanisms……………………………………………………….…. 27 2.4.3.1 Close Access Method……………………………………………….… 27 2.4.3.2 Open Access Method……………………………................................ 28 iv 2.4.3.3 Hybrid Access Method………………………………………………... 28 2.5 Cognitive Radio Technique………………………………………………..…….… 30 2.5.1 Cognitive Networks Functions………………………………………….…… 31 2.5.1.1 Spectrum Sensing…………………………………………………….. 32 2.5.1.2 Spectrum Sharing……………………………………………………... 32 2.5.1.3 Spectrum Decision……………………………………………….…… 33 2.5.1.4 Location Identification………………………………….……………. 34 2.5.1.5 Network Discovery…………………………………………………… 34 2.6 Cognitive Network Management…………………………………………………. 34 2.6.1 Centralised Network Architecture…………………………………………… 34 2.6.2 Distributed Network Architecture……………………………….…………… 36 2.6.3 Hybrid Network Architecture………………………………….…………….. 37 2.7 Cognitive Femtocell in LTE Systems……………………………………..………. 38 2.8 Technical Challenges……………………………………………………………… 41 2.8.1 Spectrum Decision and Allocation Efficiency………………………….…… 41 2.8.2 Providing QoS Awareness over an Internet Backhaul………………………. 43 2.8.3 Resource Management and Network Planning……………………………… 44 2.8.4 Interference Optimisation Problem……………………………………….…. 44 2.8.5 Mobility Problems…………………………………………………………… 47 2.8.6 Self-Organisation and Power Efficiency Challenges………………………... 48 2.9 Conclusion………………………………………………………………………… 49 2.10 References……………………………………………………………………..…. 50 Chapter 3: Spectrum Management in Cognitive Radio Systems 56 3.1 Introduction………………………………………………………….…….………. 57 3.2 Related work………………………………………………………………………. 58 3.3 Problem Formulation……………………………………………………………… 61 3.3.1 Free Channel Occurrence…………………………………………………….. 61 3.4 System Model……………………………………………………………………... 62 3.4.1 Spectrum Sensing Model…………………………………………….............. 64 3.4.2 Interference Avoidance Module……………………………………….…….. 66 3.4.3 Spectrum Decision Making…………………………………………….……. 67 3.4.4 Scheduling Mechanism………………………………………………………. 69 3.5 System Implementation……………………………………………………………. 74 3.5.1 Integrating the New Cognitive System………………………………………. 75 3.5.1.1 Generate Management Process Model………………...……………… 78 v 3.5.1.2 Generate Spectrum Resource Model……………………...………..…. 79 3.6 System Performance……………………………………………………………….. 80 3.6.1 Results………………………………………………………………………... 81 3.7 Spectrum Utilisation based Bandwidth Allocation……………………………..…. 86 3.7.1 Channel Allocation in LTE and femtocell……………………………...….… 86 3.7.2 Queuing Mechanism…………………………………………………….…… 88 3.8 System Model based Priority Spectrum Allocation……………………………….. 89 3.8.1 Spectrum Allocation Technique………………………………………….….. 90 3.8.2 System Assessment………………………………………………………….