Research On The Theory And Method Of Inter-system Double Difference Ambiguity Forming And Fixing For Multi-GNSS

Due to the complementarity among different GNSS and the increase in the number of observable satellites,multi-GNSS integration can not only improve the accuracy and reliability of positioning,but also enhance the availability and timeliness of the GNSS.So many research teams are dedicated to research in this field.One of the core topics of multi-GNSS integration is to solve the problem of differential ambiguities forming and fixing between two satellites from different GNSS.The solution of this problem is important for improving the performance of the multi-GNSS integration,especially in the special area and time interval when a single-GNSS observing satellite is rare.In this thesis,the double difference(DD)ambiguity among any GNSS,different wavelength and on the condition of different baseline length can be formed and fixed.A unified multi-GNSS combined positioning model with inter-system DD ambiguity fixing is proposed.The impact factors of inter-system bias(ISB)and the stability of ISB are systematically analyzed.The rapid estimate method of the phase-bias parameter at the GNSS receiver end is established,and the phase-bias parameter include phase inter-frequency bias(IFB)and phase ISB parameter.The method of inter-system DD ambiguity under long baseline condition is established.Based on those theoretical studies,multi-GNSS tight combining data processing system has been designed and developed independently to access the full capabilities of the multi-GNSS and multi-frequencies.By comparing the results of single-GNSS,multi-GNSS loose combining and multi-GNSS tight combining data processing in simulated and real complex observation environment,the theory and method of inter-system DD ambiguity forming and fixing is demonstrated in terms of correctness,flexibility,reliability and the superiority of processing data under complex observation environments.The specific work and major contributions of this thesis include:1.Considering the effect of IFB,ISB and different wavelength on the inter-system DD amb:iguity,a unified multi-GNSS combined positioning model with inter-system DD ambiguity fixing is established based on the classical intra-system DD positioning model.The effect of different wavelength on the inter-system DD ambiguities fixing is analyzed,establishing the method of rapid separation between phase-bias and ambiguity,realizing parameters solving and ambiguity fixing.2.The impact factors of ISB stability are analyzed in theory,and ISBs among different GNSS are divided into three groups base on the criterion of giving priority to combine overlapping or adjacent bands from different GNSS,on this basis,the ISB stability test scheme is designed.The ISB stability of GPS-BDS,GPS-GLONASS,GPS-Galileo and BDS-Galileo in the first frequency band,the second frequency band and the third frequency band are tested and analyzed by using the unified multi-GNSS combined positioning model.The test results indicate that the code ISB can remain stable at all times,the phase ISB can remain stable for the continuous observation period.Compared with other factors,the receiver restart has a great effect on the phase ISB.The main reason for this phenomenon is that the initial phase bias for different GNSS satellites does not coincide with each other in a same GNSS receiver,which causes the change of phase ISB after the receiver restart and phase ISB is not stable enough.3.By analyzing the relationship between the phase-bias parameter and the RATIO value,the multi-dimensional phase-bias estimation problem comes down to solve the optimization problem.The particle swarm optimization(PSO)algorithm is one of the optimization methods,which is used to estimate the multi-dimensional phase-bias parameters rapidly and synchronistically,on this basis,the rapid estimate method of the phase-bias parameter based on PSO algorithm is designed.The accuracy and efficiency of the method is verified by the 1-dimensional and 4-dimensional phase-bias parameter estimation experiments.The experimental results show that the average number of searching per epoch is only 9 times and the ambiguity-fixing success rate is 97.8%for one-dimensional IFB rate parameter estimation.For the 4-dimensional phase-bias parameter estimation,the average number of searching per epoch is 178 times,the ambiguity-fixing success rate is 100%,and the average calculation time per epoch is only 0.12s.The experimental results show that the method can meet the requirements of high precision real-time dynamic positioning.4.The un-combined observations are used to form the multi-GNSS relative positioning model under long baseline conditions.The effect of different wavelength and ionosphere delay residuals on the inter-system DD ambiguity fixing is analyzed.PSO algorithm is used to search the optimal value of the single difference(SD)ambiguity of reference satellite,which can eliminate the effect of different wavelength.For the effect of the ionosphere delay residuals,firstly,the:float SD un-combinatorial ambiguities are mapped into DD extra-wide-lane or wide-lane ambiguities,fixed them by LAMBDA method,and then improve the accuracy of SD un-combinatorial ambiguities by the fixed solution of DD extra-wide-lane or wide-lane ambiguities,weaken the effect of ionosphere delay residuals on the inter-system DD ambiguity fixing.On the basis of the proposed method,the general process of the inter-system DD ambiguity fixing method under long baseline condition is designed,and the calculation results of 50km baseline at low latitude and 75km baseline at mid-latitude show that the inter-system DD ambiguity fixing under long baseline conditions can be achieved by using this method,and which can meet the requirements of real-time positioning.5.Multi-GNSS inter-system DD ambiguity forming and fixing method have applied to the data processing of GPS,GLONASS,BDS and Galileo.In order to check the performance of this method,the GNSS observation data was collected in the complex observation environment,and which was processed by the proposed method.The static and dynamic observation data under the simulated and real complex observation environment condition were tested.The statistical analysis was carried out by using the success rate of ambiguity fixing,the correct rate,the positioning accuracy and the percentage of positioning difference in different precision intervals.The result show that the multi-GNSS inter-system DD ambiguity forming and fixing method is fit for complex observation environment and the software based on this method is reliability.