Research On Algorithms Of Frame And Timing Synchronization In OFDM Systems

Orthogonal Frequency Division Multiplexing(OFDM) has been extensively used in the areas of wireless mobile communication for its high spectral efficiency, high data rate and good performance for resisting multipath interferences, and has been the key technology of the 4th generation mobile communications. Combined with multiple access technology, OFDMA has been paid more and more attention, which extends OFDM to multiple users'communications. Now, OFDM/OFDMA have been the main physical technology in IEEE802.16 systems. They are sensitive to the time and frequency offset due to their special frame structures. So there is a high requirement for the orthogonality between their subcarriers. That is the reason that timing synchronization in OFDM/OFDMA systems is choosen as the topic in this thesis.After introducing the development and research status of OFDM system, the importance of timing synchronization to the OFDM is presented. In the 2nd chapter, the thesis describes the system model of OFDM and some related technologies, followed by the system model of wireless channel as well as time and frequency dispersion. In the next chapter, synchronization principle of OFDM is presented, based on which the influences of carrier frequency offset, symbol timing offset and sample synchronization offset to OFDM performance is illustrated. The ML algorithm based on CP, and Schmidl&Cox, Minn and Park algorithms based on training symbols are provided in the 4th chapter. Then their advantages and disadvantages are compared in the simulations. Finally a novel synchronization algorithm based on polyphase sequences is proposed to solve the subpeak problem of Park algorithm, followed by a timing synchronization device. Then a simulation is performed to verify results. In the following chapter, the OFDMA system based on the IEEE802.16e system is put forward. And its synchronization technologies and strategies are analyzed. A novel scheme, by means of studying the weakness of M. Morelli scheme which is a classical scheme for the uplink timing synchronization of OFDMA systems, is proposed. And a related simulation is conducted for comparison and analysis. In the last chapter, a summary for the thesis is included, and a further research direction is also suggested.