Research On Interference Suppression For OFDM Based Cognitive Radio

With the continuous development of wireless communication technology and wireless business,the requirement of wireless communication data rate is higher and higher that leads to the rapid increase of the demand for radio spectrum.The scarcity of frequency spectrum resources has become increasingly prominent.However,there are a lot of free spectrum in the existing spectrum of wireless communication system,both in time and in space.In order to solve the problem of shortage of spectrum resources and improve the spectrum efficiency,cognitive radio(CR)technology is becoming one of the best alternative.CR network can improve the utilization of licensed frequency band.Cognitive users use the licensed bands in opportunistic manner.Spectrum sensing and error free data transmission are the two main aspects in cognitive radio system.Orthogonal Frequency Division Multiplexing(OFDM)scheme is widely used in wireless communication which can fulfill the basic requirements of CR.It has many advantages such as reducing inter symbol interference(ISI)and increasing data rate.OFDM modulation technology has been used in cognitive radio(CR)systems to deal with two major issues of CR,the inter symbol interference(ISI)and the slow data rate.OFDM based cognitive radio technology has become the new focus in the current research and development of wireless communication.The main contents of this thesis are as follows.Firstly,basal concepts and basal theories of cognitive radio was introduced.Principle of OFDM and studies of synchronization technology was discussed.Secondly,a improved CP based symbol synchronization algorithm was proposed.Thirdly,a preamble-based time synchronization method which is robust against narrow band interference was studied.Finally,the study about the opportunity detection performance of energy detection with timing misalignment in UL-OFDMA is presented.