Research On Interference Cancellation In OFDM Cognitive Radio Systems By Joint Time-Frequency Methods

By allowing cognitive users access authorized spectrum opportunistically,cognitive radiotechnology improve the utilization of spectrum resources However,cognitive users must bringinterference to authorized users inevitably．In bad cases,authorized user can not finishcommunication because strong interference by cognitive users Cognitive users use NC-OFDMand we assume authorized users use OFDM,SO the problem of spectrum sharing will change intothe allocation of sub-carrier and the interference will chmage into ICI The chapter II of thepaper not only analyzes the cause of interference between cognitive users and authorized users,but also gives the relevant interference modelsThe chapterⅢof the paper introduce the technology of frequency domain partial responsefor the interference of OFDM_CR system Compared with OFDM_CR system without partialresponse coding,the performmace of OFDM_CR system will improve not only from the sidelobeenergy leakage of NC-OFDM signal spectrum of cognitive users but also the characteristics ofthecognitive user'S anti-frequency offset With the increase of the PRC series,the performance willprogressively improve but slowly Both of the theoretical analysis and computer simulation show-that the introduction of frequency-domain partial response can effectively reduce the interferenceofthe cognitive users to authorized usersOn the basis of partial response coding,the chapterⅣof the thesis join time-domainwindowing technology to improve out-of-band radiation of the cognitive users The thesiscompares three Nyquist window--shaped from out--of-band radiation of the cognitive users and theinfluence of CIR ofthe authorized users Compared with the tradition rectmagnlax window,the RCwindows and the BTRC window can reduce out-of-band radiation of the cognitive users andincrease the CIR of authorized users Computer simulation show-that the joint frequency-domainpartial response and Nyquist window can improve the cognitive user interference to authorizedusersfurther．...