Multi-cell Downlink Communication Frequency Synchronization And Compensation Technique

Orthogonal Frequency Division Multiplexing(OFDM) is a Multi-Carrier Modulation system with high spectrum efficiency, robust capability of decreasing multi-path interference and suitable for high rate data transmission, which is the key technology of the 4G wireless system. OFDM system demands strictly synchronization which is the most important and difficult in OFDM system. Synchronization accuracy will affect the entire system performance, carrier frequency offset can severely damage the orthogonality of subcarriers, so the completion of the carrier frequency synchronization is particularly important.In this thesis, we study the multi-cell OFDMA system downlink synchronization, which bases on OFDM technology and inherites the disadvantage that is sensitive to frequency offset.First, we study the principle of OFDM and its key technology:synchronization, PAPR problem, channel estimation. We study and sum up the various synchronization techniques, including the symbol synchronization, carrier synchronization, sample rate synchronization. Then we sum up the advantages and disadvantages of OFDM technology, researching state of synchronization. According to whether the use of aided data, the synchronization can be divided into two methods. The first is the data-aided. The advantages of this method are capture fast, high precision, suitable for packet data communications, the disadvantage is reducing the data transmission efficiency. The second is non-data aided, the blind estimation. This algorithm uses the structure of OFDM signal. Finally, we introduce the OFDMA system, the best preparation for later research work.Second, we study the frequency offset estimation, by improving existing algorithms to design a new preamble structure. The receiver can simultaneously estimate multi frequency offset of the base station, the performance is very satisfactory, and with the low computation.Finally, we study the question of the frequency offset compensation. Algorithms have been mostly in the frequency domain, by constructing ICI matrix, ICI matrix inversion, matrix multiplication to complete compensation. This compensation algorithm must use high computation. we attempt to complete frequency offset compensation in the time domain, which can reduce computation and the simulation results can verify the possible of this algorithm.