The Research Of Frequency Offset In OFDM Cooperative Systems

In recent years, as a hot research point in the wireless communications, OFDM Cooperationcommunication systems had attracted a great deal of attention. OFDM system has the orthogonalitybetween sub-carrier. The orthogonality of the OFDM system between sub-carries is destroyedwhich can produce significant inter-carrier interference (ICI), when the carrier frequency offsets(CFOS) happens. The OFDM system itself is sensitive to the frequency offsets; in addition, thelocal oscillator between every different cooperative spots in the cooperative communication hasfrequency offsets. Therefore, the inter-carrier interference has a more serious influence on theperformance of OFDM cooperative communication system. This paper mainly focused on how tomitigate the ICI in the OFDM cooperative communication system.Firstly, This paper establishes the model of an OFDM cooperative communication system.Then, this paper analysis how the inter-carrier offsets happen and the influence on the wholesystem. this paper introduces several common methods which can suppression the ICI andanalysis their advantages and disadvantages in the cooperative OFDM system. Then introduced themethod of frequency domain response to the cooperation OFDM system to solve frequency offsetproblem, and some simulations are done to help analysis its performance. Through the analysis ofthe bit error rate and inter-carrier interference (CIR) under different CFOS prove that the method offrequency domain response can effectively suppress ICI in OFDM cooperative communicationsystemThen, this paper introduces the SFBC-OFDM cooperative system. Some simulations are done toanalysis its performance. In SFBC-OFDM Cooperation communication, two adjacent subcarriersorthogonal structure in an OFDM symbol, so it can resist ICI interference. Then introduce twokinds of self-cancellation technology: adjacent data invert self-cancellation technology and adjacentdata conjugate algorithm. The ICI self-cancellation technology and space-frequency coding is bothused in OFDM cooperative communication to further inhibit the ICI, The simulation results showthat this method can help inhibit the ICI.