Study On Synchronization Technology Of OFDM System

OFDM is a high-speed multi-carrier transmission scheme, which is robust to multipath fading and has high spectrum efficiency. As a B3G or 4G communication technology, it attracts wide attention and has been adopted in many wide-band wireless digital communication standards. Comparing with single carrier system, OFDM system has a number of orthogonal sub-carriers. Synchronization offset would cause severe Inter-Channel Interference (ICI) and Inter-Symbol Interference (ISI). Therefore, synchronization is extremely crucial to OFDM systems. The synchronization techniques for OFDM systems are studied in this thesis.To begin with, the research background and research status of task are presented. Thereinto, the research background includs the development, application, the advantages and disadvantages of OFDM technology. The principle of OFDM system is also described, including basic characteristics, principle of modulation and demodulation, guard interval and cyclic prefix, model of OFDM system. In addition, the key technologies of the OFDM system are introduced. The synchronization principle and the effects of synchronization offset on demodulation performance are discussed in theory and simulations are done, including frequency offset and timing offset. The emphases are focused on the synchronization algorithm in OFDM technique. And this thesis studies, analyses and compares some synchronization algorithms. Many simulations are taken in AWGN and multipath fading channel, the performances are given by simulation results, and some conclusions are given. Then a new estimation algorithm of frequency offset which combines repeated PN sequence and cyclic prefix is proposed and discussed in detail and the simulation results are given. In this algorithm, repeated PN sequence is used for coarse frequency synchronization ,and cyclic prefix is used for fine frequency synchronization. Compared with the algorithm that only useing repeated PN sequence, the proposed method has more precise estimation and larger estimation range. The simulation results show that the performance of this method is evidently improved in AWGN and multipath fading channel.