| LTE (Long Term Evolution) technology has been extensively studied since its standardization by 3GPP in 2004. It is estimated that global TD-LTE users will reach 1.4 billion by the end of 2017 due to China's TD-LTE operators' vigorously promotion and leading role wordwide. Software Defined Radio is one of the main reference technologies for LTE devices with it's development. LTE cell search and downlink synchronization technology is the first step in the UE access to the cell, and its performance directly affects the LTE network performance and user experience.Therefore, this thesis mainly focuses on TD-LTE cell search and downlink synchronization technology, and designs a TD-LTE cell search and downlink synchronization scheme, and achieve it on the Software Defined Radio platform, which mainly includes the following aspects:1. Based on the LTE physical layer frame structure and synchronized signal, the basic methods of realizing frame timing synchronization in LTE systems are analyzed.2. Detailed schemes for TD-LTE cell search and downlink synchronization are studied and devised. The detection algorithm of PSS (Primary Synchronization Signal)correlation detection and segmentation correlation detection is researched from the aspects of computational complexity and anti-frequency-deviation. In the study of frequency synchronization, two kinds of fractional frequency offset estimation algorithms are compared in terms of frequency offset estimation range and performance.A low complexity blind detection algorithm is researched as for the detection of CP type.The detection algorithm of SSS (Secondary Synchronization Signal) traditional blind detection and the general detection is analyzed, and its detection performance is improved by channel estimation with the PSS signal before the SSS detection. The simulation of the entire program shows that when the signal to noise ratio is greater than 4dB, the synchronization accuracy is almost 100%.3. Finally, the most popular software radio GNURadio + USRP platform is selected to implement and verify the proposed scheme. The key algorithm is optimized with the Intel SSE instruction set, reducing the time complexity by about 50%. The synchronization accuracy is as high as 99.7% in practical environment test.Based on the research and implementation, the proposed TD-LTE cell search and downlink synchronization scheme proves valueable in practical applications. |
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