Optimization Design And Implementation Of NB-IoT Cell Search Function Based On Synchronous Detection

Narrow Band Internet of Things(NB-IoT),with its advantages of low power consumption,low cost,wide coverage,and support for massive connections,has become an important branch of low-power wide-area Internet of Things.Cell search,as the first physical process of mobile devices access to the cell,has an important impact on the performance of NB-IoT systems.However,as there is no cell grouping technology in NB-IoT and the structure,function and generation method of synchronization signal are quite different from that of traditional cellular network,the difficulty of cell search is increased,and the detection accuracy of synchronization signal used for frequency,timing synchronization and carrying cell information is reduced.Therefore,with the increase in the number of IoT terminal devices and the increase in communication quality requirements,how to quickly and accurately establish the NB-IoT cell search function based on synchronous detection has become one of the important problems that need to be resolved for the terminal to establish a communication link with the base station.To solve the above problems,based on synchronous detection,this thesis improves the cell search process and optimizes the detection algorithms of NB-IoT primary synchronization signal(NPSS)and NB-IoT secondary synchronization signal(NSSS)respectively.First,in the NPSS detection stage,the data is down-sampled using the good auto-correlation and cross-correlation characteristics of NPSS,and sliding auto-correlation is performed at a low sampling rate,which reduces the amount of data calculation.In addition,in order to solve the problem that the peak value of correlation value of synchronization signal is not obvious,this thesis proposes the idea of taking the variance of correlation value,which further improves the detection accuracy of NPSS.Secondly,in the NSSS detection stage,the NSSS generating function is reasonably split and processed item by item.According to the rule that the phase offset changes with the frame number,an independent calculation module is designed to replace the complex multiplication calculation with the phase shift of a special angle.It reduces the algorithm complexity and avoids the tedious data reading at the same time,which effectively improves the performance of cell search.In this thesis,we first build a Matlab simulation platform to verify the integrity and effectiveness of the cell search function based on synchronous detection.Furthermore,the link-level simulation function based on the platform of OAI(Open Air Interface)was selected to build the OAI+USRP B210 test platform,and the NB-IoT cell search function designed in this thesis was tested and verified.The test results show that the detection accuracy rate of the synchronization signal is 98%,and the detection accuracy rate of the cell ID is 96%,which is improved compared with the matched filter detection and has reached the expected design index.