Research And Implementation Of LTE Cell Search Algorithm

With the development of the society, the quantity of the subscribers has grown sharply, which makes the spectral resource increasingly exiguous. In consideration that the close combination to the Internet is the following development direction of the mobile communication, the existing 3G technology can no longer satisfy the requirements of the times. Therefore, in recent years, the 3rd Generation Partnership Project(or 3GPP in abbreviation), has launched the biggest technical research project. In LTE(Long Term Evolution), the initial cell search is the pre-requisite for the user equipment to create downward link with the base station. Meanwhile, the fundamental purpose of the cell search is to make the user terminal capture the time and frequency synchronism of its actual cell, and then recognize the ID number of the cell.First of all, this paper presents the introduction of the LTE demand index as well as the analysis of the cell search rearch status. It emphatically elaborates the OFDM technology and the influences of the time deviation and frequency deviation.Second, it proposes the detailed study of the cell search process. This process canbe divided into six steps, namely, rough time synchronization, CP type checking, decimal frequency offset estimation, integer frequency offset estimation, and the detecting algorithm of SSS. The common rough time synchronization algorithm consists of the auto-correlation algorithm based on PSS and the cross-correlation algorithm based on PSS. The improved algorithm is proposed to solve the problem that the performance of the conventional PSS correlation algorithm decreases dramatically under the large frequency offset. The rationale for the improved algorithm is to incorporate three primary synchronization signals into a new synchronization signal by utilizing the good performance of the ZC sequence’s auto-correlation and cross-correlation, then correct the frequency deviation of the received signals and make correlation. The improved algorithm can still capture the timing location of PSS even though the frequency deviation is large. The CP type judgement is mainly composed of the blind detection based on SSS and the auto-correlation detection based on CP. The frequency deviation estimation is classified as decimal frequency deviation estimation and integer frequency deviation estimation. The frequency deviation includes the decimal frequency offset estimation and the integer frequency offset estimation. The decimal frequency offset usually adopts the CP cyclic prefix and the PSS correlation algorithm. The PSS primary synchronization signal estimation is usually employed for the integer frequency deviation in the frequency domain, while the frame synchronization is more often than not obtained via detecting the secondary synchronization signal SSS. The contrast simulation of various algorithms in the process is conducted on the Matlab simulation platform. This thesis analyses the influences of various factors including SNR, channel environment, and frequency offset to the timing detection performance, frequency detection accuracy, and cell ID detection under different algorithms.Last but not the least, by taking into account of the performance and complexity of all the algorithms, the multiple functions ranging from the half-frame synchronization, sector detection, CP type recognition, frequency deviation estimation and compensation, and SSS detection are achieved with the design of the LTE cell search process. The core of the LTE cell search process is embodied in the synchronous timing detection algorithm based on the cross-correlation PSS, and the frequency deviation estimation algorithm.Based on the CP cyclic prefix.Based on the above algorithm, this paper presents the implementation of LTE cell search by using Xilinx XC7K330 T chip at the same time the function of main modules is proposed. Research shows that the fixed-point over the FPGA platform can approach the same performace close to that is obtained by using the float-point LTE cell search program.