The Analysis And Simulation Of Sensing Spectrum Technologies In Cognitive Radios

Cognitive Radio (CR) is a new intelligent wireless communication technology, which is viewed as a potential approach for improving the utilization of a precious radio spectrum,because of its ability of changing its transmitter parameters immediately based on interaction with the environment where it operates, especially it enables unlicensed users to use licensed spectrums. It should be noted that spectrum sensing is not only a primary task, but also a notable character of CR. After introducing some fundamental concepts of cognitive radios, this dissertation simulates several sensing spectrum methods; then researches on cooperation scheme; and last discusses their applications in IEEE 802.22.Firstly, this dissertation summarizes fundamental notions of cognitive radios, including its definition, concept model, main functions and important technologies. With regard to sensing spectrum techniques, spectrum-hole, interference temperature and their relationships are presented. Then the dissertation classifies sensing spectrum into two parts, transmitter detection and cooperative detection.Secondly, regarding the first part of sensing spectrum technologies, transmitter detection, this dissertation systematically investigates three digital signal processing techniques: matched filtering, energy detection, and cyclostationary feature detection. In addition, considering AM and DS signals under different signal to noise ratios, this dissertation makes modeling and simulation for various detection techniques. Our analysis shows that energy detection does well in saving time, whereas cyclostationary feature detection has its advantages due to its ability to differentiate modulated signals, interference and noise in low signal to noise ratios. Bases on above analysis, we present a novel improved technique for sensing spectrum.Thirdly, this dissertation shows the benefits of cooperation in cognitive radios, which is second part of sensing spectrum technology. Considering a simple two users cooperative cognitive network, it shows improvement in agility by exploiting the inherent asymmetry. We then extended our cooperation scheme to multi-user multi-carrier networks and stated precise conditions under which agility gain is achieved. We analyzed two cooperative schemes employing varying degrees of cooperation: entire non-cooperative and partial cooperative. We found that for multi-carrier networks, asymptotically there is no difference between the cooperation scheme and partial cooperative scheme. Compared with entire non-cooperative scheme, however, the agility gain of our cooperation scheme was found to be great.Finally, this dissertation analyses IEEE 802.22 standard. Based on cognitive radio technology, this standard is required to reuse the TV spectrum without causing any harmful interference for existed TV services and provides cheaper services to non-authorized user. In this dissertation, for designing physical layer, the applications of sensing spectrum technologies in IEEE 802.22 standard are analyzed in detailed.