The Research On Downlink Initial Cell Search Algorithm Of FDD-LTE System

Long Term Evolution (LTE) project is considered as the next generation evolution of3G technology, which achieves a smooth transition from the3G (3rd Generation) to B3G(Beyond Third Generation) and4G(4rd Generation). LIE achieves the higher data rates, the lower latency, the lower costs, the higher system capacity and the larger coverage. The initial cell searching process is the premise of establishing the downlink communication between terminals and base stations. In order to get time and frequency synchronization and the cell ID (IDentity) information of the right cell, terminals rely on the cell search process with cell searching commands, so the efficient algorithms and performances research for cell searching become the key point of access technique. The essence of the cell searching algorithms is to achieve the detection of synchronization channel, which obtains the time, frequency synchronization and cell ID number.Firstly, the thesis introduces the history and development of LTE standard, synchronization technique of OFDM (Orthogonal Frequency Division Multiplexing) system and cell searching technique of LTE system. Based on the affects of time and frequency error in FDD-LTE (Frequency Division Duplexing Long Term Evolution) system, background and significance of the synchronization detection algorithm are introducesd. In addition, several classical synchronization algorithms, such as the S&C algorithm, Minn algorithm and Park algorithm and so on are listed and discussioned.Then, the initial cell searching process is studied in detailed. The algorithms and simulations of the frequency offset estimation, frequency offset correction, the primary synchronization channel estimation and the secondary synchronization channel detection have been performed in this thesis.After that, the primary synchronization signal sequence has been re-designed based on its features in FDD-LTE system. The original primary synchronization detection algorithm of cell searching has been optimized. Meanwhile, an improved low complexity method has been researched, and the proposed algorithm can greatly reduce the computation of sliding in the original primary synchronization detection algorithm and improve the timing detection efficiency.Finally, the performances and simulations of the secondary synchronization signal detection algorithm have been studied. Two different algorithms are presented:one is the cross-correlation detection method based on good correlation of the secondary synchronization signal, and the other is the algorithm based on fast Hadamard transforming. The results of simulation show that the performance of fast Hadamard transforming based algorithm is superior to the good-correlation based cross-correlation detection method.