Study On Spectrum Sensing And Second User Ivioiiitoring In Cognitive Radio

With the rapid development of wireless communication technologies, the spectrumresources are becoming increasingly scarce. Cognitive radio (CR) is considered as the keytechnology in next generation of wireless communication, since it enables opportunisticspectrum access. This thesis focuses on a research on a series of key technologies of spectrumsensing and second user monitoring in CR, including spectrum sensing, second user monitoringbased on Medium Access Control (MAC) layer in IEEE802.22standard, and Wireless RegionArea Network (WRAN) system simulation.The main contributions and innovations are listed as follows.1. Advantages and disadvantages of several common decision criteria and spectrum sensingalgorithms are concluded. Occasions for decision criteria and algorithms are also discussed indetail.2. A modified spectrum sensing algorithm based on maximum and minimum eigenvalue isproposed for blind detection in a small-scale network. This algorithm introduces a differentialpreprocessing, rebuilds a test statistic and obtains a constant false alarm rate (CFAR) thresholdaccording to numerical analysis methods. Simulation results show that the algorithm canevidently reduce the network’s scale while achieve the same detection performance.3. A dynamic cooperative spectrum sensing algorithm based on fractal dimension isproposed. In order to overcome the drawbacks caused by the unreliability of each sensing nodesin the network, this algorithm optimizes local sensing algorithm and scale of networkrespectively. Since communication signal and noise are different in irregular degree, they can bedescribed and distinguished by fractal dimension. This thesis builds a test statistic and derives adecision threshold. Meanwhile, this article also designs a strategy for adjusting sensingnetwork’s scale dynamically. Experimental results indicate that novel algorithm is hardlyaffected by circumstance and maintains detection capability even when most of the nodesdeployed in low SNR scenes.4. A method based on MAC layer in IEEE802.22standard is proposed for monitoringsecond users in CR. Firstly, feasibility of monitoring is discussed after studying the architectureof IEEE802.22standard and MAC layer technologies. Then factors associated with the seconduser behavior are summarized, and the key words in MAC frames are located and extracted.Finally, a method is designed according to the instructions from base station.5. A system level simulation platform of WRAN is implemented with MATLAB. The overall framework of simulation platform is combined with several modules, each of whichexecutes a certain function. The corresponding design philosophies and the related concreteimplementation schemes are provided. Tests are implemented in order to corroborateperformance of algorithms mentioned before, and the experimental results are all expected.