At present,micro-positioning Navigation and Timing(micro-PNT)system is a highly concerned technology development direction at home and abroad,and will play an important role in national security,military and civil fields in the future.The miniature atomic clock(MAC)with high precision,low power consumption and small volume is the core and key of the development of micro-PNT system.It has high application potential and value in the areas of unmanned aerial vehicle,auto-driving,communication,single-fighter operation and so on.This paper studies the clock offset modeling and prediction method based on the noise spectral density of chip-scale atomic clock(CSAC),studies and implements the GNSS domestication CSAC algorithm,designs the CSAC-assisted GNSS positioning and timing test scheme,and gives the qualitative and quantitative analysis results through experiments.Finally,a micro positioning and timing terminal is designed and implemented by using CSAC,GNSS chip receiver and STM32 microcontroller.The detailed research contents are as follows:(1)The CSAC clock offset is tested for a long time.The stability and accuracy performance of CSAC are analyzed,and the characteristic parameters of CSAC are extracted.Then,according to the relationship between time-domain frequency stability and frequency-domain energy spectrum noise,the main random noise affecting CSAC is further analyzed and its noise intensity coefficient is calculated.(2)By analyzing the noise spectral density of CSAC,the clock offset modeling and prediction method based on Kalman filter are studied.Based on this,a CSACassisted GNSS positioning algorithm based on receiver clock offset prediction is designed,and a CSAC-assisted GNSS positioning test platform is built to verify the impact of using CSAC and internal TCXO as GNSS receiver reference clock source on positioning results.The results show that the horizontal and vertical positioning errors of the external CSAC receiver within 5 minutes are 0.48 m and 0.88m(RMS),respectively,when the satellite navigation is interrupted(the number of effective visible satellites is reduced to 3);When using TCXO inside the receiver,the assisted positioning error of clock offset reaches 100 meters.It is proved that the CSAC assisted positioning can ensure the continuity and accuracy of positioning when the visual conditions of satellite navigation are not good.(3)The method of GNSS disciplined CSAC is studied,and a ping-pong control algorithm with time-holding function is designed.When the reference signal is valid,the CSAC is control periodically to keep synchronization with the GNSS system time.When the reference signal is invalid,the CSAC is maintained for a period of time.Finally,taking the control result of third-party clock control software as reference,the clock control algorithm designed in this paper is tested and verified.The test results show that the clock steering algorithm designed in this paper can control the fluctuation range of the clock offset between CSAC and GPST at-7.5~7.5ns,which is better than that of third-party software control algorithm-11.15~11.31 ns.1h frequency accuracy is,which is better than of third-party software control algorithm.Within one day,the autonomous clock holding capacity was 372.21 ns,which effectively suppressed the influence of clock frequency deviation,while the cumulative clock offset of third-party software control algorithm was 13.05μs.In addition,the short-term stability of CSAC in τ=1-300s is better than that of third-party software control algorithm after the control of ping-pong algorithm.(4)Based on the above research results,the overall scheme of micro positioning and timing terminal is designed.A terminal hardware circuit with seven function modules as the core is constructed,including time difference measurement module,power module,GNSS receiver module,etc.And a terminal micro controller program and upper computer test software are written.Finally,a micro positioning and timing terminal with real-time data collection,calculation and storage functions is implemented. |