Study On Cell Search Algorithm Of LTE System

To meet the challenges of WIMAX(Worldwide Interoperability for MicrowaveAccess) and other that of mobile broadband communication technologies, maintainingthe UMTS(Universal Mobile Telecommunications System) technology competitiveadvantage in the next decade or even longer,3GPP started the standardization ofLTE(Long Term Evolution) in2004, LTE immediately got a lot of attention andresearches. As the first physical layer process of UE access to cell, LTE cell searchbecame a hotspot in recent years. The physical layer process includes time andfrequency synchronization, as well as the accessing of cell identification and a series ofother key system parameters, Cell search performance affects the establishment ofsubsequent communication link directly. Accordingly, it is very necessary to research onthe LTE cell search in depth.On the basis of surveying on the research status at home and abroad of LTE cellsearch and studying the principle of OFDM(Orthogonal Frequency DivisionMultiplexing), this thesis analyses the ICI(InterCarrier Interference) andISI(InterSymbol Interference) caused by synchronization error. Obtaining the effect onBER through simulation to verify the importance of synchronization techniques forOFDM system. Thesis also discusses the LTE physical layer downlink PrimarySynchronization Signal、Secondary Synchronization Signal and downlink referencesignal, and their mapping position in the time-frequency domain. On these bases, thesisproposes a set of precise and fast LTE cell search algorithm flow.Against the coarse timing synchronization performance of traditionalcross-correlation algorithm based on PSS decreases sharply in a large frequency offset,this thesis proposes a improved M-part correlation algorithm, Although there is someloss of signal-to-noise ratio by simulating, the improved algorithm is more robust tofrequency offset. Using the ML(maximum likelihood) algorithm to detect cell sector IDand cyclic prefix type and designing a fractional frequency offset、integer frequencyoffset and residual frequency offset estimation in three steps of frequencysynchronization process. Basing on researching the fine timing synchronizationalgorithm of OFDM system, this thesis uses Yang algorithm as the LTE cell search finetiming synchronization and proposes its design criteria. To improve the SSS detectionperformance in high-speed mobile environment, this thesis explores the structure advantages of SSS sequence of cyclic shift and interleaving mapping, implementingSSS differential correlation detection algorithm. The SSS detection performanceverification has been greatly enhanced compared with traditional coherent algorithm.At last, This thesis verifies the performance of each key algorithm by simulatingthe LTE cell search algorithm, and points out that the cell search almost does not affectthe performance of LTE system in Gaussian channel. When in mobile multipath channel,comparing with the ideal performance, the signal-to-noise ratio of cell search algorithmloses only a few dB. The result shows that the proposed LTE cell search algorithm canmeet the performance requirements.