Detection of Vacant Frequency Bands in Cognitive Radio
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MEE10:58 DETECTION OF VACANT FREQUENCY BANDS IN COGNITIVE RADIO Rehan Ahmed Yasir Arfat Ghous This thesis is presented as part of Degree of Master of Science in Electrical Engineering Blekinge Institute of Technology May 2010 Blekinge Institute of Technology School of Engineering Supervisor: (Doktorand) Maria Erman Examiner: Universitetslektor Jörgen Nordberg ii ABSTRACT Cognitive radio is an exciting promising technology which not only has the potential of dealing with the inflexible prerequisites but also the scarcity of the radio spectrum usage. Such an innovative and transforming technology presents an exemplar change in the design of wireless communication systems, as it allows the efficient utilization of the radio spectrum by transforming the capability to dispersed terminals or radio cells of radio sensing, active spectrum sharing and self-adaptation procedure. Cooperative communications and networking is one more new communication skill prototype that permits the distributed terminals in a wireless network to cooperate with each other through some distributed transmission or signal processing in order to comprehend a new appearance of space diversity to contest the detrimental effects of fading channels. In this thesis, we regard the relevance of these technologies to spectrum sensing and spectrum sharing. One of the most vital challenges for cognitive radio systems is to diagnose the existence of primary (licensed) users over an extensive range of spectrum at a particular time and explicit geographic locality. We consider the utilization of cooperative spectrum sensing in cognitive radio systems to increase the consistency of detecting of primary users. We describe spectrum sensing for cognitive radios (CRs) and project a vigorous cooperative spectrum sensing procedure for a practical framework employing cognitive radios Cooperative sensing can formulate excellent use of network assets, attain higher gain and make the network smooth. In this thesis we give a concise introduction of the principle of cooperative sensing and discuss the cooperative sensing techniques in CRs. Simulation results confirm that cooperative sensing can get better detection probability, can advance the agility gain and as a result finally help with more efficient utilization of spectrum. iii iv ACKNOWLEDGEMENTS All thanks to Almighty ALLAH who is not only the creator and the owner of this universe, but also the most merciful, beneficent and the most gracious, who provided us guidance, strength and abilities to complete our thesis successfully. We are thankful to the Faculty Staff of the school of engineering of the BTH; they were a light of guidance for us in our whole study period at BTH, particularly in building our base in education, enhancing our knowledge and sharpening our practical skills. We are especially thankful to Ms. Maria Erman, our thesis supervisor, for her help, guidance and support in completion of our project. Our everlasting gratitude and acknowledgements are for our parents for their moral support and encouragement throughout ourr study period at BTH. v vi TABLE OF CONTENTS List of Acronyms ........................................................................................................................................... x List of Figures ............................................................................................................................................xiii List of Tables .............................................................................................................................................. xiv 1. Introduction ................................................................................................................... 1 1.2 Background & Thesis motivation.................................................................................................... 2 1.3 Problem statement ........................................................................................................................... 3 1.4 Thesis Outline ................................................................................................................................. 3 2. Literature Review ................................................................................................................. 4 2.1 Introduction ...................................................................................................................................... 4 2.2 Cognitive Radio ................................................................................................................................ 4 2.2.1 Motivation and Requirements : .................................................................................................... 5 2.2.2 The Cognitive Radio operation ................................................................................................ 5 2.3 Software Defined Radio ................................................................................................................... 6 2.3.1 SDR and its Relationship with Cognitive radio .......................................................................... 6 2.4 The Cognitive Radio Network Architecture .................................................................................... 7 2.4.1 Primary network .......................................................................................................................... 7 2.4.2 Cognitive radio network .............................................................................................................. 8 2.5 Spectrum Sensing ............................................................................................................................. 9 2.5.1 Methods ..................................................................................................................................... 10 2.5.2 Challenges ................................................................................................................................. 10 2.6 Spectrum Management ................................................................................................................... 10 2.6.1 Spectrum analysis ...................................................................................................................... 10 2.6.2 Spectrum decision ..................................................................................................................... 11 2.6.3 Spectrum management challenges ............................................................................................ 11 2.7 Spectrum mobility .......................................................................................................................... 12 2.7.1 Spectrum Hando ff ...................................................................................................................... 12 2.7.2 Spectrum mobility challenges .................................................................................................... 13 2.8 Spectrum Sharing ........................................................................................................................... 14 2.8.1 Classification of spectrum sharing ................................................................................................ 14 vii 2.8.2 Spectrum sharing challenges.......................................................................................................15 2.9 OFDM Based Cognitive Radio..........................................................................................................16 3. SPECTRUM SENSING TECHNIQUES .............................................................................. 18 3.1 Introduction .................................................................................................................................... 18 3.2 Spectrum Sensing ........................................................................................................................... 18 3.3 Multi-Dimensional Spectrum Sensing ........................................................................................... 19 3.4 Challenges ...................................................................................................................................... 21 3.4.1 Hardware Requirements ............................................................................................................ 22 3.4.2 Hidden Primary User Problem .................................................................................................. 22 3.4.3 Detecting Spread Spectrum Primary Users ............................................................................... 23 3.4.4 Sensing Duration and Frequency .............................................................................................. 24 3.4.5 Decision Fusion in Cooperative Sensing ................................................................................... 25 3.4.6 Security...................................................................................................................................... 25 3.5 Spectrum Sensing Methods for Cognitive Radio ........................................................................... 26 3.5.1 Energy Detection ........................................................................................................................ 26 3.5.2 Matched Filter ........................................................................................................................... 27 3.5.3 Cyclostationary Detection ........................................................................................................