Research On Synchronization Technology Of OFDM System And Fixed-point FFT Algorithm

Wireless communication technique becomes the emphasis of communicationresearch, and more and more people focus on it. Orthogonal frequency divisionmultiplexing(OFDM) technology has been applied widely in wireless communication,it not only can resist the multi-path fading, but also can greatly increase thetransmission rate of wireless communication system and spectral efficiency. But asthe subcarriers of OFDM system are orthogonal, OFDM system is very sensitive tosynchronization errors, so it is essential for OFDM system to keep accuratesynchronization. In addition, OFDM system uses IFFT/FFT algorithm to realize themodulation and demodulation, in order to simplify the hardware implementation andimprove running speed, it is necessary to research the fixed-point realization of FFT.At first, the dissertation presents the fundamental principle, system model andfeatures of OFDM technique and discusses the synchronization algorithms in detail.For synchronization algorithms, data assisting and no-data assisting algorithms areanalyzed respectively, the focus of this dissertation is data assisting algorithm. Basedon the analysis of the deficiencies of classical algorithms S&C and Minn, three newtraining sequences have been designed, and new timing metric functions have beenpresented as well. From the results of simulation, it can be concluded that the threenew training sequences have an impulse-shaped timing metric for different cyclicprefix length and resolve the problems of S&C and Minn algorithms. Moreover, forthe last two new training sequences, frequency offset estimation functions have beenpresented. It can be concluded that the new frequency offset estimation algorithmcould enlarge frequency offset estimation range while maintaining the estimationaccuracy, and they still have superior performance for low signal-to-noise ratio(SNR).Secondly, this dissertation introduces three basic algorithms of Fast Fouriertransform (FFT) and overflow processing of fixed-point FFT. Based on Welch’smethods, a novel method for overflow processing has been proposed. In the proposedmethod, overflow detection module is put in the beginning of each butterfly, and theinputs of this butterfly are detected，in addition, only one test is needed in eachbutterfly. From the results of simulation, compared with Welch’s methods, it can beconcluded that the proposed method could save a number of bits for achieving thesame performance in the same simulation environment. The proposed method is not only accuracte in calculation but also simple in realization. At last, the dissertationanalyses the influences of fixed-point FFT without overflow processing andfixed-point FFT with overflow processing on communication systems, from thesimulation results, it can be concluded that it is essential to do overflow processing forfixed-point FFT.