Research On LTE Cell Search Techniques Based On Matched Filtering

LTE Cell Search is the first step for the mobile station to get the time and frequency synchronization, and acquire the cell ID. This is a very ciritical progress, because it is the premise for the user to establish the communication links with the base station. Only with the acquisition of the synchronization and cell ID, information send by the base station can be received and decoded at the receiver, and other information send by other base stations can be filtered. With the difference from traditional 3G systems, LTE communication system needs to support the system bandwidthes range from 1.25MHz to 20MHz. So the synchronization for LTE system can not be achieved by scanning the channel, which results into the further research on LTE cell search.In order to achieve the LTE cell search fast and accurately, this thesis started with the study of the synchronization algorithm and the cell ID detection algorithm, then the impact on OFDM system by the synchronization is analyzed. Not data-aided synchronization algorithm and data-aided synchronization algorithm are both studied, and the former has the advantages of high data rate and spectral efficiency, but it brings about the problems of computational complexity, long acquisition time, and low accuracy, even in the scene of large multi-path delay, this algorithm is disabled. The latter needs to occupy more spectrum resources. In this thesis the synchronization algorithm based on training sequence is studied especially, which has the advantages of high capture speed, accuracy, and flexibility. For the quick acquisition of cell ID, cell group also adopted.The thesis also focuses on the improvement algorithm existing, and proposed a simplified LTE cell search scheme: (1) Since the timing deviation and fractional frequency offset will occurred in the received signal, the half frame coarse timing, FFO, and cell ID can be estimated according to the peak detection of the correlation values of the received signal by local primary synchronization signal (PSS). (2) If we get the OFDM symbols from the position by the half frame timing, then transform it into the frequency domain by FFT, the samples offset will occurred, and a phase factor will attached for the timing error. In view of the problem, an joint estimation of timing error and integer frequency offset is used to reduce the complexity of the algorithm. (3) Take into the strategy of cell group, cell group ID shoud be detected, besides, the frame starting position need to be determined. Which can be achived by the secondary synchronization signal (SSS). For the sake of apply to both of the two dulplex modes TDD and FDD, this thesis locates the SSS by mathing the local SSS with the received signal, Instead of coherent detection.Finally, under the scenarios of the common communication, feasibility study on the LTE cell search scheme is carried out, and simulations prove of the validity of the algorithm. In the end, this thesis summarized the work I have done, pointed out the remaining problems and gave some prospect for the next phase of work.