Research On Downlink Cell Search Algorithm Of TD-LTE

LTE was put forward by 3GPP to satisfy the demand of next gerneration. OFDM is the key technology of LTE. Its basic theory is that transfer high-speed serial transmission to low-speed parallel transmission. OFDM system is sensitive to little synchronization errors. When the system was affected by synchronization error, the orthogonality between subcarriers was destroyed and cause interference between subcarriers. So synchronous technology is critical to the system.Cell search is a synchronization process that UE obtains the time and frequency synchronization and cell ID with the serving cell when UE initial accesses the cell or UE is in the process of handovering cells. Cell search is the critical step in the mobile communication system. Under the premise of the mobile terminal reading the base station information, the mobile terminal can establish a communication link with the serving cell. The performance of cell search will directly affect normal communication of the whole system. Only the cell search complete successfully, can the normal data exchanging between the UE and a base station be ensured.Firstly, the article carries out the research on process about synchronization and algorithm of cell search in downlink about TD-LTE. Then build the simulation link about synchronization in downlink.Finally, achieve the physical-layer cell-identity group detection by FPGA.Chapter1 describes the overview of the development of the mobile communication firstly. Then introduce the key technology of LTE.Finally, determine the contents and structure of this article.Chapter 2 describes the basic theory of the synchronous technology in downlink.First elaborate the basic theory of OFDM system and specifically analyze the impact of time delay and frequency offset.Then introduce the frame structure of LTE, the composition of cell ID and the generation principle of PSS and SSS. Finally research self-correlation and cross-correlation between synchronization signals.Chapter 3 research on cell search synchronization algorithm. Describe the cell search procedure and design the low-pass filter and downsample. Then research fourcategories of synchronization algorithm. There are two kinds of the timing delay estimation detections which named the coarse timing delay estimation detection and the fine timing delay estimation detection. Also frequency offset estimation detections include three types algorithm that are called the fractional part frequency offset estimation, the interger number of sub-carrier spacings frequency offset estimation and the left frequency offset estimation. Then the detection of CP types is considered which are named blind CP detection and correlation CP detection. Lastly do some study on SSS detection methods which include three types. Then improve the traditional ML estimation algorithm so that expand the using range of ML estimation. In the end of this chapter build the simulation link with Matlab. Contrast the simulation performance of the synchronization algorithm that are mentioned before in different channels.Finally this article have the conclusion that synchronization algorithm based on PSS performs better than ML estimation algorithm. So synchronization algorithm based on PSS is chosen for hardware implementation.Chapter 4 is the study about FPGA implementation for the physical-layer cell-identity group detection. Non-coherent detection is the implementation method.Firstly describe the whole downlink SSS detection module.Secondly analysis each module in detail. Thirdly the function simulations of the important module by using ModelSim are given.Finally achieve the physical-layer cell-identity group detection by FPGA.Chapter 5 is the conclude of this article. Then put forward the future research direction.