A SOFTWARE DEFINED RADIO TESTBED FOR RESEARCH IN DYNAMIC SPECTRUM ACCESS A Thesis Submitted to the Faculty of Purdue University by David A. Clendenen In Partial Fulfillment of the Requirements for the Degree of Master of Science in Engineering May 2012 Purdue University Fort Wayne, Indiana ii For my uncle, Jeffrey Davis, who instilled in me from a young age the desire to learn how things work and inspired me to become an electrical engineer. iii ACKNOWLEDGMENTS I first thank Dr. Todor Cooklev for providing me with the opportunity to expand my engineering background to the world of wireless communications and software defined radio. I appreciate his patience and flexibility in working with me as I balanced my career, graduate courses and this research. Next, I thank my graduate committee; Dr. Chao Chen and Dr. Yanfei Liu and my thesis format advisor, Barbara Lloyd for their support and direction in my thesis writing. I also thank Dr. Elizabeth Thompson for first informing me of the National Science Foundation grant and Dr. Donald Mueller and Dr. Carlos Raez for selecting me as a recipient for the grant. I would also like to thank my colleagues at Regal Beloit and my manager, Dr. Roger Becerra, whose support and flexibility allowed me to accomplish my professional and educational goals. I thank my parents for always encouraging me and instilling in me the value of hard work. Most importantly I thank my wife, Tish, for her encouragement and understanding throughout my graduate studies. Above all else, without her support none of this would have been possible. iv TABLE OF CONTENTS Page LIST OF FIGURES .......................................................................................................... vii LIST OF ABBREVIATIONS ..............................................................................................x ABSTRACT ....................................................................................................................... xi 1. INTRODUCTION ..........................................................................................................1 2. SOFTWARE DEFINED RADIO ..................................................................................3 2.1 Definition .................................................................................................................3 2.2 SDR Architectures and Testbeds .............................................................................3 3. THE UNIVERSAL SOFTWARE RADIO PERIPHERAL ...........................................5 3.1 Introduction to the USRP .........................................................................................5 3.2 Features of the USRP ...............................................................................................5 3.3 Compatible Software Packages ................................................................................7 3.4 GNU Radio ..............................................................................................................7 3.4.1 GNU Radio and the USRP ...............................................................................8 3.4.2 The GNU Radio Companion ............................................................................9 3.5 Simulink-USRP......................................................................................................10 4. COGNITIVE RADIO AND DYNAMIC SPECTRUM ACCESS ..............................13 4.1 Spectrum Allocation Models .................................................................................13 4.1 Cognitive Radio .....................................................................................................14 4.2 Introduction to Dynamic Spectrum Access ...........................................................15 4.3 Spectrum Opportunity Identification .....................................................................15 4.4 Spectrum Opportunity Detection ...........................................................................16 4.4.1 The a priori model ..........................................................................................16 4.4.2 Spectrum measurement and sensing ...............................................................16 4.5 Spectrum Opportunity Tracking ............................................................................17 4.6 Spectrum Opportunity Exploitation .......................................................................18 v Page 5. SPECTRUM SENSING ...............................................................................................19 5.1 Spectrum Sensing Techniques ...............................................................................19 5.1.1 Coherent detection ..........................................................................................19 5.1.2 Cyclostationary feature detection ...................................................................20 5.1.3 Energy detection .............................................................................................20 5.2 Cooperative Spectrum Sensing ..............................................................................22 6. SDR TESTBED DEVELOPMENT .............................................................................25 6.1 Description of Testbed ...........................................................................................25 6.2 Energy Detector Implementation ...........................................................................25 6.2.1 GNU Radio implementation ...........................................................................26 6.2.2 Simulink-USRP implementation ....................................................................26 7. SPECTRUM PROBING AND PROBING DELAY ...................................................28 7.1 Description of Spectrum Probing ...........................................................................28 7.2 Spectrum Probing Methods....................................................................................29 7.3 Description of Probing Delay ................................................................................30 7.4 Theoretical Analysis of Probing Delay ..................................................................33 7.4.1 Independent perfect detection .........................................................................33 7.4.2 Independent imperfect detection .....................................................................34 7.4.3 Cooperative perfect detection .........................................................................35 8. TESTBED IMPLEMENTATION: MEASUREMENT OF PROBING DELAY ........36 8.1 Overview ................................................................................................................36 8.2 Primary User Emulation ........................................................................................36 8.3 Signal Synchronization ..........................................................................................37 8.4 Probing Implementation.........................................................................................38 8.4.1 Cognitive radio network emulation ................................................................40 8.5 Data Analysis .........................................................................................................41 8.5.1 Independent sensing ........................................................................................44 8.5.2 Cooperative sensing ........................................................................................44 9. SIMULATION AND EXPERIMENTAL RESULTS .................................................47 9.1 Simulation Results of Probing Delay .....................................................................47 9.2 Experimental Results of Probing Delay: Perfect Detection ...................................51 9.2.1 Independent sensing results ............................................................................51 9.2.2 Cooperative sensing results ............................................................................57 vi Page 10. CONCLUSIONS AND FUTURE WORK .................................................................63 10.1 Future Work ...........................................................................................................64 10.1.1 Probing delay under imperfect detection .......................................................64 10.1.2 A DSA-enabled CR transceiver .....................................................................65 10.1.3 Advanced spectrum sensing methods ............................................................65 10.1.4 Spectrum sensing with radio learning .............................................................65 LIST OF REFERENCES ...................................................................................................67 APPENDICES A. GNU RADIO SUPPLEMENTAL INFORMATION ..................................................70 A.1 A transmitter with GNU Radio and the USRP ......................................................70 A.2 A receiver with GNU Radio and the USRP ...........................................................71 A.3 The GNU Radio Companion .................................................................................71 B. USER-DEFINED MATLAB SCRIPTS AND FUNCTIONS .....................................74 B.1 Matlab Embedded Function: Detector ...................................................................74 B.2 Matlab Script: simulink_spect_probing_UI ...........................................................76