| With the rapid development of wireless network, more and more radio spectrum resource will be needed. Cognitive radio is an exciting emerging technology to improve spectrum efficiency, by which, the licenced spectrum resource can be shared dynamically by cognitive user. The accurate and effective spectrum sensing is the key of realizing the cognitive radio, which are the research hotspots in wireless sphere.Under the support of Foundation (Design and research on cognitive radio system to anti interference for military use), National Science and Technology Major Project of China (2009ZX03002-009-01) and National Science Foundation of China (60672132,60872149), the spectrum sensing technology and corresponding application in CRN are deeply investigated in this paper. The main contributions of the dissertation are as follows:(1) The parameters influencing the system performance are closely related in cooperative spectrum sensing and detection threshold is an important factor, which is usally obtained through simulation comparison other than given algorithm. In this paper, the relationship among SU, detection threshold, bandwidth, spectrum utilization and secondary throughput in cognitive radio networks is analyzed in the point of bandwidth for the first time. An optimal algorithm for selecting detection threshold is proposed, by solving the mathematical model, the maximized secondary throughput can always be achieved while assuring sufficient protection to primary user.(2) In CSS, more secondary user leads to much control bandwidth occupied for sending the local sensing results, and the tail sensing problem will also become serious when the reporting channel suffer from deep fading. To deal with this limitation, a censoring based CSS is proposed and an optimal detection algorithm suggested for further from the point of secondary user. The analytical results show that the control bandwidth can be effectively saved, the dependence of reporting error to sensing user number can also be reduced by C-CSS. The tail sensing problem can be effectively solved and the false alarm probability also decreased. The maximized spectrum access chance of secondary user can be realized while assuring target detection probability by optimal algorithm. In addition, C-CSS performance from the point of secondary user throughput is analyzed for further. The relationship among SU, detection threshold, bandwidth, spectrum utilization and secondary throughput is studyed and the optimal algorithm for maximizing the secondary throughput is proposed. The research results indicate that the required detection threshold for maximizing the secondary throughput is different between traditional CSS and C-CSS under given SU number while assuring object detection probability. The larger secondary throughput can be achieved with less SU in C-CSS. The optimal secondary throughput can be realized by the proposed optimal algorithm.(3) The system performance will be degraded by channel fading, which can be effectively solved by relay cooperation. In order to improve the transmission reliability, an object based cooperative spectrum sensing scheme with best relay (Pe-BRCS) is proposed, in which the best relay is selected by minimizing the probability of reporting error to improve the sensing performance. Numerical results show that, the proposed Pe-BRCS can make the reduced reporting error probability and the false alarm probability lower bounds. The sensing performance can be improved with little computational complexity compared with SINR-BRCS. At present, the fully cooperation occasion is considered in relay cooperation in which the higher system cost is needed. In order to save the system expense in actual occasion, an adaptive cooperative spectrum sensing scheme with best relay (ABRCS) is proposed, where, the target SU can adaptively decide whether the relay’s cooperation is needed according to its reporting channel condition. Results illustrate that the best sensing performance can always be achieved by ABRCS whether SU’s reporting channel is good or not.(4) The detection performance can be effectively improved by soft combination compared with hard combination in CSS. According to the deflection that much control bandwidth will be occupied in CSS based on soft combination with data fusion, which leads to the reduced spectrum utilization, in addition, the imperfect reporting channel has not been considered at present. The actual occasion with both imperfect sensing channel and reporting channel is considered in this paper. A CSS based on soft combine with decision fusion (SC-DF-CSS) is proposed and the detection performance is analyzed for further. At last, the optimal algorithm to obtain the weighting vector is given. The results show that, only a little detection performance loss exists in SC-DF-CSS compared with SC-EF-CSS. The detection performance could be effectively improved by the optimal algorithm, and the optimal algorithm based on modified deflection coefficient can achieve the same performance with the optimal algorithm based on N-P criticism, which make the complexity reduced greatly.(5) The purpose of doing research on the performance of spectrum sensing is to make it applicable in actual. At present, the inter cell interference coordination method can not break through the regulatory spectrum architecture, and the cell edge user’s rate is hard to be promoted. As a frequency programming technology, the cognitive radio technology can make the optimal resource configuration to improve the spectrum utilization by sensing the surroundings intelligently. Accordingly, a inter cell interference coordination method based on spectrum sensing technology is proposed in this paper, where, the terminal with cognitive function can automatically detect the available spectrum when requesting for service, and select the idle spectrum or the occupied spectrum with the weakest signal strength to realize the actual weakest interference communication, make the reduced inter cell interference and improved cell edge user’s performance. |
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