The Study Of Synchronization Technique For OFDM And Its FPGA Realization

Recently, OFDM (Orthogonal Frequency Division Multiplexing) technique has been paid more and more attention because of its strong transmission ability in wireless channels, which comes from the orthogonal properties among its sub carriers, its parallel transmission mechanism and inherited strong robustness to ISI (Inter Symbol Interference) in the multi-path channel. However, OFDM system is so sensitive to frequency offset, timing error and phase noise that a tiny synchronization offset may lead to the deterioration of the BER (Bit Error Rate) performance of system, even communication failure. As a result ,in order to reduce the effects of system performance due to synchronization error, frequency offset, timing error and phase error need to be estimated and compensated effectively in both time and frequency domain when designing the synchronization module of OFDM receiver.The basic theory, distinguishing features and advantages of OFDM are presented in this thesis. A detailed theoretical analysis and MATLAB simulation are employed to discuss the effects of timing offset, carrier offset and sampling offset on OFDM system. And the effect of symbol timing offset on channel estimation which is based on pilot is also presented. The rough symbol timing synchronization algorithm, fine symbol timing synchronization and sampling timing algorithm and frequency algorithm are analyzed in both time and frequency domain, and a new way of symbol timing in the multi-path channel is proposed, and all of the three algorithms are analyzed and compared with use of MATLAB simulation.The bandpass undersampling theory and the detailed mathematical reasoning of bandpass undersampling digital quadrature coherent demodulation are presented in this thesis, and a digital IF receiver of OFDM system is presented. The digital receiver is with larger dynamic range, higher I, Q output precision, using bandpass undersampling method for IF sampling, digital filtering method digital quadrature coherent demodulation.Finally, according to the performance requirements of the sync-system, a full synchronization system is designed on the basis of full consideration to the performance of algorithms and realization complexity, and the realization structure of the various synchronization algorithms using in the synchronization system of OFDM are described in detail. The ModelSim and FPGA simulation results of partial hardware realiztion are presented in this thesis.