Research On High Precision Wireless Time Synchronzations Technology For TC-OFDM

In complex indoor environment,because of the obstruction of roof and wall,the quality of GPS satellite signals is poor,and it is impossible to provide accurate location services.TC-OFDM system is a high-precision seamless location system,which meets the needs of high-precision and diverse location services.Outdoor,TC-OFDM system uses outdoor base station to broadcast location signals;indoor,TC-OFDM system uses indoor distributed system to broadcast location signals.With the help of outdoor base station and indoor distributed system,TC-OFDM system can achieve seamless coverage of indoor and outdoor positioning signals.High-precision time synchronization technology is a necessary prerequisite to ensure that TC-OFDM indoor distributed system broadcasts positioning signals synchronously,and it is also a necessary condition for TC-OFDM system to provide accurate positioning services.Aiming at the problems of inaccuracy of the existing wireless time synchronization methods and the tedious distribution of wired time synchronization networks,a high-precision wireless time synchronization system for indoor distributed system is designed and realized,which realized the sub-nanosecond relative time synchronization accuracy.The system is divided into two parts:Acquisition of High Precision Reference Frequency Source for Main Node and the time synchronization technology based on Ultra Wide Band between indoor nodes.Aiming at the problems of low carrier frequency acquisition accuracy in high precision reference frequency source acquisition method and high time measurement noise in complex environment in Ultra Wide Band time synchronization technology,theoretical innovation research and engineering practice are carried out.The main research contents and achievements of this paper are as follows:(1)To solve the problem of low carrier frequency acquisition accuracy in high precision reference frequency source acquisition method,a frequency estimation method based on cubic spline interpolation is proposed.This method uses multiple parallel down converters and integral unit zero-cleaners to down convert and integrate the stored RF signals with multiple local frequencies.The integration results are fitted by cubic spline interpolation algorithm,and the residual carrier frequency estimates are finally obtained.The simulation results show that,on the premise of consuming the same hardware resources,the average frequency estimation error of this algorithm is about 1/3 of that of the existing methods.(2)Aiming at the problem of high time measurement noise in complex environment based on Ultra Wide Band time synchronization method,a Proportional Integral Derivative control method based on Kalman filter is proposed.Simulation results show that this method makes full use of the statistical characteristics of time measurement noise and reduces the impact of time measurement noise on synchronization accuracy.Compared with the classical Proportional Integral Derivative control method,this method can improve synchronization accuracy by 3 7.41%.(3)The time synchronization subsystem based on Ultra Wide Band was designed and implemented,and a phase closure tracking loop based on time measurements Kalman filter、Proportional Integral Derivative and clock tame was constructed.The time measurement whole-cycle hopping correction model is designed.The coarse synchronization method based on DW1000 internal system counter and the time measurement method based on the sender-receiver hybrid mode are proposed.The simulation and measured results show that under the condition of using 16 bit DAC and 1e-9/s voltage-controlled temperature-compensated crystal oscillator with short-term stability and setting the calibration time of 0.6 s at the same time,the ultra-wideband time synchronization subsystem can achieve better than ±0.5 ns relative time synchronization accuracy.In summary,this paper firstly proposes a frequency estimation method based on cubic spline interpolation to solve the problem of low carrier frequency acquisition accuracy in high-precision reference frequency source acquisition method;secondly,a proportional-integral-differential control method based on Kalman filter is proposed to solve the problem of high time measurement noise in complex environment in time synchronization method based on ultra-wideband.Thirdly,a high-precision wireless time synchronization system for TC-OFDM indoor distributed system is designed and implemented,which solves the problem of high-precision wireless time synchronization for TC-OFDM.