ABSTRACT
The number of mobile users is increasing day by day in the current wireless communication scene, which may certainly create bandwidth crises due to limited spectrum availability. Cognitive radio (CR) is a future technology capable of solving the spectrum scarcity problem. In a cognitive radio network (CRN), the unlicensed CR users use the unused licensed band of primary users (PUs) while a PU is not active. The available sensing methods to detect the spectrum are matched lter detector, energy detector (ED), and cyclostationary feature detector [1-7]. Both matched lter and cyclostationary feature detections provide better performing results under low signal-to-noise ratio (SNR) in wireless communication systems but they require the PU’s prior information. An ED is one of the most popular detectors for spectrum sensing (SS), also known as the blind SS technique. This technique does not require the prior information of a PU’s signal and has low computational
CONTENTS
7.1 Introduction ........................................................................................................................ 119 7.2 Problems in CRNs .............................................................................................................. 120 7.3 Related Works ..................................................................................................................... 120
7.3.1 Adaptive SS ............................................................................................................. 120 7.3.1.1 Limitations ............................................................................................... 121
7.3.2 Two-Stage Detection Scheme ............................................................................... 121 7.3.2.1 Limitations ............................................................................................... 121
7.4 Proposed Scheme ............................................................................................................... 122 7.4.1 SNR Estimation-Based SS Scheme ...................................................................... 122
7.4.1.1 Energy Detector with Single Threshold ED ........................................ 124 7.4.1.2 Energy Detector with Adaptive Threshold (ED with ADT) ............. 125 7.4.1.3 Adaptive Threshold Schemes for Spectrum Sensing ........................ 126
7.5 Simulation Results and Analysis for ESNR_ADT Scheme .......................................... 130 7.6 Collaborative Spectrum Sensing with Proposed ESNR_ADT Detector .................... 133 7.7 Simulation Results and Analysis for CSS Using ESNR_ADT Detector ..................... 135 7.8 Conclusion and Future Work ........................................................................................... 136 Acknowledgments ...................................................................................................................... 136 References ..................................................................................................................................... 136
complexity, but does not perform well at a low SNR. Similarly, there are also some other limitations in a CRN such as the SS failure problem, sensing time, hidden terminal problem and shadowed effect by severe multipath fading. To resolve these problems, we proposed a sensing scheme known as estimated SNR with adaptive threshold where we sense the PU signal under low SNR, mitigate the sensing failure problem, and have a quick sensing time. In addition, using the collaborative sensing scheme with the proposed estimated SNR sensing, we resolve the hidden terminal problem and shadowing effects.
