Research On Synchronization Method For OFDM Based On Training Sequence And Its Application In CMMB System

OFDM modulation makes use of many parallel sub-carriers transmitting lower speed data to realize high speed communication. And it has the merits of effectively resisting the frequency selective fading and impulse noise of channels. However, OFDM system is quite sensitive to the frequency offset caused by Doppler Effect and the instability of oscillators. The frequency offset will damage the orthogonality of the sub-carriers of the OFDM system, and cause the inter-carrier interference (ICI). Therefore, the synchronization of the time and the frequency is the key factor that determines the performance of the OFDM system.As a newly developed multimedia service, China Mobile Multimedia Broadcasting (CMMB) has been widely concerned. It is issued by the State Broadcasting Film and Television Administration on October 24,2006, as the standards of the industry. CMMB system uses the Orthogonal Frequency Division Multiplexing (OFDM) technology and makes the best use of its advantages, highly efficient frequency spectrum and resistant to frequency selective fading caused by multi-path interference, to realize transmit audio frequency and video frequency information with rather high speed.This thesis mainly discusses synchronization techniques of OFDM system and proposed two timing synchronization methods based on training sequence. Then, the thesis analyzes the frame structure of the CMMB physical layer and proposes a joint synchronization technique for CMMB system. The thesis mainly consists of three parts as below:1. Research on OFDM synchronization technique:this part briefly discusses the principle of OFDM system and presents the synchronization technique of OFDM system including symbol timing synchronization and carrier frequency synchronization and proposes two timing synchronization methods based on training sequence. Finally, the character of wireless channel is introduced and the channel module used to test the performances of the proposed method in this thesis has been given.2. Analysis of the frame structure of the CMMB physical layer:this part first gives the definition of the frame structure of the CMMB physical layer. Then, the forming process of the CMMB frame signal is simulated by matlab after the analysis on the frame structure of CMMB in order to have a profound understanding of it.3. Research on synchronization technique of CMMB:By reference to the frame structure of CMMB physical layer and the analysis in the first part, this part proposes a joint synchronization technique for CMMB system after analyzing and contrasting. Finally, the proposed methods are simulated to verify the method and test the performances using matlab. At last, a hardware scheme of the method is proposed.