Study On Symbol Timing Synchronization And Frequency Synchronization In OFDM Communication Systems

In order to obtain the goal of communicating information by broad band with any manner, in any place and at any moment, the future wireless communication requires the characteristics of high quality, high reliability and high transmitting rate. The technology of OFDM is concerned increasingly due to its advantage such as high spectral utilization rate and the ability to oppose the multi-path interference. It is already widely applied in Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), IEEE 802.11a WLAN and IEEE 802.16 WCAN. It will become the core technology of the fourth mobile communication.However, OFDM systems are extremely sensitive to synchronization error. When synchronization error exits,Serious Inter-Carrier Interference and Inter-Symbol Interference is introduced and demodulation performance will be degraded greatly. So fine synchronization is essential to OFDM systems. This dissertation studies on the symbol timing synchronization and frequency synchronization for OFDM systems. A lot of computer simulations are given over AWGN and frequency selective fading channels. We analyze and compare the performance of a few synchronization methods, including their applied areas, merits and shortcomings. Furthermore, the article proposes an OFDM synchronization algorithm based on cyclic prefix. This timing synchronization algorithm simplifies maximum-likelihood algorithm neglecting the correlation coefficientρ,which is related to SNR. Therefore, it can be applied for the case that SNR is unknown. It made use of the product of correlation and its conjugate. So it can simplify hardware, avoid complicated mode operation. In order to improve performance of this method over frequency selective channel, we average over several symbols. The simulations show that this multi-symbol simplified synchronization algorithm significantly reduces the mean square error of timing estimate. The main content of the dissertation is:Chapter one: introduction. It introduces the transmitting characteristic of wireless fading channel ,the history and current situation of OFDM technology.Chapter two introduces in detail the basic principle of OFDM systems, including its advantages, shortcomings and key technologies.Chapter three discusses and analyses the effects of synchronization errors on demodulation performance, including frequency offset , timing offset and sampling frequency offset.Chapter four studies on symbol timing synchronization methods. It can be divided into two types: based on the cyclic prefix and training sequences .It analyzes and compares the estimated performance of a few classical methods, proposes a simplified maximum-likelihood synchronization algorithm and improves the...