Research On Positioning Technology Of NB-IoT Terminal

Since the release of standard of Narrow Band Internet of Things(NB-IoT),increasing NB-IoT-based Internet of Things(IoT)applications have emerged in our daily life.These applications can be found in various areas,such as smart home,intelligent transportation,smart healthcare,intelligent logistics and so on.Statistically,about 70%of the IoT applications directly depend on or benefit from location information of devices,which makes positioning technology become one of key technologies that promote large-scale commercial applications of IoT.Considering the system characteristics and deployment scenarios of NB-IoT,this thesis studies Time delay estimate(TDE)algorithm and positioning algorithm respectively that are applicable to NB-IoT terminal.The main work in this thesis can be summarized as follows:Accuracy of traditional TDE algorithms in single-path channel is limited by sampling rate.A two-level TDE algorithm is proposed in this thesis to solve this problem.Firstly,integer time delay is obtained by using time-domain autocorrelation properties of Narrowband Positioning Reference Signal(NPRS)sampled at different rates.Secondly,based on integer time delay compensation,signal is transformed to frequency domain to estimate fractional time delay utilizing phase difference of subcarriers.Simulation results show that proposed algorithm breaks bound brought by sampling rate and achieves higher accuracy.In order to overcome the problem that NPRS transmitted from neighbor cell towers and multipath components from target cell cause severe interference to TDE of first arrival path(FAP)in multipath channel.This thesis presents a FAP time delay estimate algorithm based on successive interference cancellation(SIC).The algorithm consists of two stages for interference mitigation.In the first stage,the Time of Arrival(TOA)of the strongest path of each neighbor cell is estimated sequentially,combined with channel coefficient estimation of the strongest path,so that the interference components can be removed from received signal.In the second stage,TOA estimation of strongest path of target cell is iteratively performed,the corresponding component is then directly subtracted from correlation of received signal.Finally,sub-sample TOA estimation is performed by interpolating correlation function.Simulation results show that proposed algorithm effectively mitigates effect of interference signals in TDE.To suppress effect of None Line of Sight(NLOS)transmission in terminal positioning,this thesis introduces a method to identify whether NLOS error is contained in TOA measurements based on standard deviation of measurements Furthermore,NLOS effect is mitigated by using improved Kalman filter to smooth and mitigate NLOS effect for TOA measurements.Besides,this thesis proposes an improved Chan algorithm.Algorithm initially assumes that TOA measurements are obtained in Line of Sight condition,then establishes residual cost function,iteratively estimates NLOS transmission distance.Simulation results show that two methods alleviate effect of NLOS transmission during the stage of TDE and coordinate calculation respectively.