Research On Time And Location Determine Techniques In Large Delay Tolerant Networks

In today's world,countries are paying more attention to exploration of space resources,and the pace of exploration is further and further away.From the Moon to Mars and to the edge of the solar system,it will inevitably beyond the solar system and enter the broader universe.In deep space exploration,it is a crucial issue for the spacecraft to don't rely on the Earth,and realize the autonomous time and location calibration technique.In terms of time synchronization,the Two-Way Synchronization Time Transfers is the highest accuracy technology in the existing system,but in the case of dynamic links,there is still a large error,and it is worth studying the corresponding correction algorithm.In terms of navigation and positioning,X-ray pulsars are capable of emitting stable periodic pulse signal.This is a popular field for deep space positioning in recent decades.Localization algorithms based on this method need practical analysis and verification when applied to specific scenarios.In this context,this paper first introduces the development of autonomous navigation and positioning,and the current research trends of X-ray pulsars.The time base and spatial reference are then described because the measurements associated with pulsars are based on the Solar System Barycenter.Afterwards,analyzing the factors that influence the time delay including the troposphere,ionosphere and Sagnac effect.Next,the basic principle of X-ray pulsar positioning is introduced in detail.Including the extraction of observation pulse contours,the conversion from the atomic time to the TCB,the Phase-Time Model,and the time delay calculation.Because the emission time of pulsar signals cannot be obtained,the basic observation equations are based on the differential positioning of spacecraft and SSB.Afterwards,the Two-Way Synchronization Time Transfers algorithm is described.However,in the case of dynamic link,the algorithm has a large synchronization error.Therefore,this paper improves it and obtains a synchronization algorithm based on pseudo-delay sequence and an algorithm based on radial velocity.Because simulation experiments require actual satellite orbital data,this paper builds ground station,satellites,and spacecraft simulation models through satellite tool kits(STK)to obtain node position,velocity,and time data,and then use it on the assumption of time bias building a simulation platform with MATLAB,to verify the performance of the proposed time synchronization algorithm.Finally,aiming at X-ray pulsar positioning,this paper proposes a positioning method based on known nodes.Since the spacecraft is close to the known node,a large-period pulsar can be selected to estimate the position of the spacecraft firstly,then bring in the remaining pulsars to estimate the ambiguity and expand the range,and then use the spatial search method to obtain the precise ambiguity.In the finally,getting the spacecraft's position coordinate.