Study On The Accuracy Improvement Of Bds Orbit Determination

Satellite orbit is taken as the space coordinate reference frame of navigation system.The on-orbit satellites are taken as the coordinate frame point.Accuracy and stabilization of orbit determination have great influence on the accuracy and reliability of navigation system.Beidou navigation satellite system(BDS)is under construction.Research on BDS orbit determination accuracy improvement is a matter of great significance.The key technology of orbit accuracy improvement is studied in this dissertation.There are three aspects: solar radiation model improvement,multi-system integration POD and POD with Inter-Satellite Link(ISL)measurements.Research in this dissertation provides some theoretical support for BDS construction.The main work and contributions are as follows:1.The research status and different solution algorithms of Orbit Determination(OD)are studied.This dissertation mainly studies on the theory of numerical orbit determination method which is widely used in navigation.The details of key algorithms during programming realization are introduced.GPS state propagator consists of a Keplerian orbit propagator accounting for secular and periodic perturbations.GPS broadcast ephemeris parameters model design based on orbit perturbation variation characteristics.Under this significance,we believe perturbation parameters of GPS broadcast ephemeris have physical meaning.We derive the formulas of broadcast ephemeris perturbation parameters under the influence of earth oblateness perturbation and lunisolar perturbation.Meanwhile,we prove the conclusion by GPS broadcast ephemeris.2.It is proved by theory and experiment analysis for the first time that ECOM 5 parameters model is more suitable for BDS POD(single-day or three days solution).The Bernese ECOM solar radiation pressure model is the most widely used empirical model.The application on BDS precise orbit determination is studied.The model parameters of ECOM are inverted by the precision ephemeris from MGEX(Multi-GNSS Experiment)which is chosen as the pseudo-observations.Time series analysis and significance testing of these model parameters are processed.The conclusion can be obtained: the 5 parameters are significant,while the other parameters are strong correlation with these 5 parameters.The experimental analysis which is processed by the measurements of MGEX proves that the 5 parameter model is more suitable for BDS POD.3.A new GPS/BDS combined PPP function model is proposed.The Inter-System Bias(ISB)parameters in fusion of GPS/BDS Precise Orbit Determination(POD)and Precise Point Positioning(PPP)are investigated.The characteristic of short and long term shows that the ISB parameters can't be deducted from the original observation which can only be solved by parameter estimation on the contrary.A new GPS/BDS combined PPP function model is put forward.Comparing with traditional model,the receiver clock bias,posteriori residuals of pseudo-range and phase ambiguity bias are changed all,while the location parameters have no influence.4.The algorithm and process of GPS/BDS combined POD is studied.The solved results are compared with the POD result only makes use of BDS observations.The comparative content is as follow: the parameters of orbit,troposphere and posteriori residuals of phase observation.We can get the conclusion that GPS/BDS combined POD improves the accuracy of common parameters in the observation equation of the two systems,especially the troposphere parameter.The POD accuracy of BDS is improved ultimately.5.Accuracy of ISL measurements of BDS new generation experiment satellites are investigated for the first time.According to the characteristics of ISL measurements of BDS experiment satellites,the derivation approach of the satellite clock offsets and the geometry distances from the TDMA dual one-way measurements without accuracy loss is studied.The derived clock offsets and geometry distances are used for time synchronization and autonomous orbit determination.The accuracy assessment of the derived measurement from the BDS experiment satellites shows that the measurement accuracy is about 6-8cm.6.The POD approach which combines ISL measurements and the L-Band ground-based code/phase measurements is studied and evaluated by measurements of BDS experiment satellites for the first time.The theory and process of this approach are shown in this dissertation.The ISL measurements during the DOY 193-207 of 2016 from BDS experiment satellites are used for experiment.We can get the conclusion: Comparing with POD only use L-Band ground-based code/phase measurements,the POD accuracy improvement ratios of radial(R),along-track(T)and cross-track(N)directions are 51.4%,59.8%,and 24.3%,respectively.The accuracy of R/T directions improves performance significantly,while the N direction is not.The POD accuracy of MEO improves significantly.7.This dissertation studies and realizes the centralized autonomous orbit determination of the new-generation BDS satellites using ISL measurements.The theory and process of autonomous orbit determination are introduced in detail.Autonomous orbit determination is processed while the Beijing station is chosen as anchor station and the arc length of orbit determination is chosen as three days.The overlapped segmental arc comparison results of five BDS experiment satellites show that Root-Mean-Square(RMS)of RTN directions are 0.124 m,0.885 m and 0.720 m,respectively.Comparing with the POD result only use L-Band ground-based code/phase measurements,the RMS of RTN directions are 0.341 m,1.595 m and 1.743 m,respectively.8.A new algorithm which reduces the error of static station measurement caused by multipath is proposed.This algorithm makes full use of the characteristics that multipath error is strong correlation with the direction of measurement.Setting the size of grid by elevating angle and horizontal angle,the mean and standard deviation of posteriori phase residuals of the grid are calculated,which model the multipath errors in this direction.Hence this algorithm can reduce the multipath error of GNSS original observations during PPP or POD.The validity of the algorithm is verified by the IGS measured data eventually.9.A new robust Kalman Filtering(KF)algorithm is proposed and used for GPS/BDS combined dynamic PPP.The principle of robust KF is to re-evaluate the contribution of each measurement to parameter estimation according to the posterior residuals.Robust KF can reject of gross errors in GNSS dynamic navigation and positioning.However,when it is applied to GPS/BDS combined dynamic PPP,the positioning accuracy may be worse than the result of single system PPP.Since the random characteristics of different satellite types are different,the posterior residuals of these measurements are different either.When the posterior residuals are applied to calculate the equivalent weight factor in robust estimation,the high quality data may be down weighted,leading to the deviation of the positioning result.To avoid such problems,the algorithm of this dissertation calculates the equivalent weight factor based on different system or satellite type.The theories and realizing flows of this algorithm are introduced in detail and verified by experiments eventually.