Study On Application Of Cooperative Communication In Cognitive Radio

One of very important development trend of mobile communication system is broadbandmultimedia communication system, however, the lack of spectrum resources and unreliability oftransmission restrictes its development. In order to solve this problem, Cognitive Radio(CR)technology was put forward. CR provides a solution for the lack of spectrum resources by reusinglicensed spectrum.Although Multiple Input Multiple Output(MIMO) system can improve reliability oftransmission, some factors such as the power and volume of mobile terminal restrict the applicationof MIMO system in practice. Therefore, Sendonaris and so on proposed cooperative communicationtechnology. Its basic idea is to make use of the cooperation between nodes in a communicationnetwork, thus sharing transmission path. Cooperative communication technology is very flexible,and it can be combined with a variety of technologies, to highlight respective advantages.The application of cooperative communication in CR is mainly researched in this paper, andthe main work and innovations are as follows:(1) Cooperative communication technology and CR technology are detailedly introduced,including their background and their research status.(2) When the primary user(PU) and secondary user(SU) share the same spectrum, in order notto interfere the PU, the transmission power of SU is very small and the outage probability of SUnetwork is very high in CR system. If SU can obtain cooperation from surrounding nodes and thebest relay set is selected, outage probability of SU network will reduce. Therefore, a best relay setselection scheme in CR system is proposed in the third chapter, and outage probability of SUnetwork based on this scheme is derived. The simulation results show that this scheme cansignificantly decrease outage probability of SU network.(3) Spectrum sensing technology is the core technology of CR system. However, theperformance of traditional spectrum sensing algorithm is poor. Although a spectrum sensingalgorithm can improve performance of spectrum sensing, it is based on high power consumption. Inorder to improve the performance of spectrum sensing and save power, the algorithm on spectrumsensing with double threshold and opportunistic cooperation is proposed in the fourth chapter andperformance of spectrum sensing based on this algorithm is derived. The simulation results showthat this algorithm can improve the performance of spectrum sensing and save power.(4) Reporting channel, channel of each SU to the fusion center, is supposed to be ideal channel in traditional cooperative spectrum sensing system. However, noise and fading must have an influenceon reporting channel, and it leads to bit error in reporting channe. That is the results transmited bySU isn’t consistent with the results received by fusion criterion. This will affect the performanceof cooperative spectrum sensing ultimately. Therefore, a cooperative spectrum sensing algorithmbased on cooperation and best relay selection is proposed in the fifth chapter. It aims at decreasingthe bit error rate of reporting channel and improving the performance of cooperative spectrumsensing. The simulation results show that this algorithm can significantly improve the performanceof cooperative spectrum sensing and.