| Observable specific Signal Bias(OSB)describes the hardware delay of carrier phase observation at various frequency points on the satellite end.Accurate estimation of OSB is the key to achieving non differential ambiguity resolution(AR)in precision point positioning(PPP),and is an important prerequisite for improving positioning accuracy and reliability.At present,the PPP-AR working group of the International Global Navigation Satellite System Service(IGS)is promoting the use of phase OSB to achieve non differential ambiguity fixation..Traditional uncalibrated phase delays(UPD)and integer recovery clocks(IRC)phase deviation products are not uniform in form and are all provided to PPP-AR users by combining the deviations.However,as the number and frequency types of satellites increase,the amount of phase deviation data in the combined form will greatly increase.In addition,when PPP-AR clients use these traditional phase deviation products,the estimated non difference ambiguity must be consistent with the phase deviation provided by the server,which will greatly reduce the compatible interoperability between the server and the client.Phase OSB can directly provide carrier phase deviation of various frequency points on the satellite in a non combined form.PPP-AR users use phase OSB products that have higher flexibility and scalability compared to traditional combined forms.However,domestic and foreign scholars have limited research on estimation methods of phase OSB,and further research is needed on how to convert different forms of phase deviation products into phase OSB compatible with traditional IGS pseudorange clock deviation.On the other hand,the vast majority of IGS analysis centers only provide dual frequency phase OSB products,which cannot fully meet the requirements of multi frequency and multi system PPP-AR.How to balance the time-varying and time-invariant hardware delay of multi frequency phase deviation within the existing IGS specification framework,and expand the multi frequency phase OSB is still a current research difficulty.At the same time,various IGS analysis centers usually use different satellite attitude models during satellite ground shadow periods,and further research is needed to achieve accurate estimation of multi frequency phase OSB during satellite attitude anomalies.Therefore,seeking a unified and concise phase OSB estimation method has become a major cutting-edge hot topic in GNSS high-precision positioning.This paper conducts in-depth research on multi frequency and multi system phase OSB estimation methods,focusing on breaking through technical challenges such as time-variant and time-invariant partial fusion processing of multi frequency phase OSB,fast or instantaneous fixed multi frequency non differential ambiguity,and proposing a more suitable multi frequency phase OSB product generation strategy for server release,and establishing a multi frequency PPP-AR fast or instantaneous positioning service system.The specific work and main contributions of this paper are as follows:(1)In order to solve the problems of inconsistent forms and various combinations of phase deviation products,two dual-frequency phase OSB estimation methods,namely UPD-OSB and IRC-OSB,which are compatible with traditional IGS pseudo-range clock errors,are proposed on the basis of dual-frequency UPD(Uncalibrated Phase Delays)and IRC(Integer Recovery Clocks)models to provide users with simple and unified phase deviation products.PPP-AR users only need to directly correct the dual-frequency phase OSB provided by the server to the original carrier phase observation value of the corresponding frequency,and use the corresponding precision orbit,pseudo-range clock error and pseudo-range OSB to directly realize PPP-AR.Based on the final precision orbit product provided by Wuhan University(WUM),the spatiotemporal characteristics of dual-frequency phase OSB and PPP-AR positioning performance of the two estimation methods are compared.The experimental results show that in terms of phase OSB stability,the UPD-OSB stability of GPS/Galileo/Beidou-3 systems is better than that of IRC-OSB because the reference of IRC clock difference and WUM pseudorange clock difference is not consistent and is absorbed by IRC-OSB.In terms of positioning performance,in view of the fact that IRC clock error is fixed with non-difference ambiguity on the basis of double-difference ambiguity constraint,further reducing the correlation of ambiguity in time and space,and improving the resolution accuracy of IRC clock products,PPP-AR using IRC-OSB is slightly better than UPD-OSB in positioning accuracy and filtering convergence time.(2)Aiming at the problem that the time-variant and time-invariant hardware delay of the L5 carrier phase of GPS Block IIF satellite is difficult to be estimated uniformly,this paper proposes a reliable and easy-to-expand multi-frequency phase OSB estimation method based on the combination of the ionosphere-free and geometry-free three-frequency phase observations.Based on the dual-frequency phase OSB,this method estimates the ambiguity of the L5 frequency point using white noise.The time-varying and time-invariant phase delay will be absorbed by the L5 ambiguity at the same time,and then the fractional part of the ambiguity can be directly used as the phase OSB of the L5 frequency point.Multi-frequency PPP-AR users only need to add the estimated multi-frequency phase OSB to the original observation value.The impact of the time-varying part of GPS Block IIF L5 on PPP-AR will be reduced,and the non-difference ambiguity of multi-frequency and multi-system can also be fixed.Combined with multi-frequency and multi-system dynamic non-combined PPP-AR test,it is shown that compared with the PPP floating point solution without multi-frequency phase OSB,the multi-frequency phase OSB can improve the positioning accuracy in the east,north and zenith directions by about1.3cm,0.8cm and 1.3cm respectively.(3)The flexibility and effectiveness of multi-frequency phase OSB in fixing the non-difference ambiguity of multi-frequency PPP are analyzed and discussed in depth.Through rigorous theoretical derivation and PPP-AR test of arbitrary frequency point combination,the results show that the estimated multi-frequency phase OSB in this paper is downward compatible with the traditional dual-frequency satellite clock error(such as Beidou-3 B1I/B3 I clock error),and the server does not need to re-estimate the clock error product.After the multi-frequency PPP-AR user corrects the multi-frequency phase OSB to the corresponding original observation value,the non-combined ambiguity or the ultra-wide lane,wide lane The fuzziness of narrow lane is subject to the normal distribution of 0 mean value,that is,the fuzziness has the integer property.Therefore,in the environment of multi-frequency observations,compared with the traditional UPD and IRC methods,this paper estimates that the multi-frequency phase OSB products will provide great convenience for the user to achieve PPP nondifferential ambiguity fixation.(4)Based on the multi-system satellite attitude quaternion products provided by WUM Analysis Center,a multi-frequency phase OSB estimation model considering the satellite yaw attitude is established,which realizes the accurate estimation of the multi-frequency phase OSB during the satellite ground shadow,and improves the reliability of the multi-frequency multi-system PPP-AR positioning.The test results show that when the solar altitude angle of the satellite orbital plane is low,the consistency between the estimated IRC clock error and the WUM pseudo-range clock error is improved by about 70% after using the WUM attitude quaternion product,and the estimated multi-frequency phase IRC-OSB jump in the satellite yaw maneuver region will be eliminated,and the single-day stability will be significantly improved.In terms of PPP-AR positioning,when the satellite is in the shadow period,compared with the nominal attitude,the positioning accuracy of PPP-AR using the attitude quaternion can be improved by about 32%,29% and 38% in the east,north and zenith directions respectively.In addition,when the number of observable satellites is large,the positioning accuracy of the satellite with the exception of yaw attitude is equivalent to that of the satellite attitude quaternion.However,when the satellite geometry is relatively poor and the number of observable satellites is relatively small(for example,Beidou-3),the positioning results will have a deviation of about 10 cm in the zenith direction after removing the satellites.Therefore,this paper suggests that the satellite attitude quaternion products of the corresponding analysis center should be used for clock offset,phase OSB estimation and PPP-AR positioning.(5)Based on the multi-frequency and multi-system phase OSB,the multi-frequency and multi-system instantaneous PPP-AR positioning system is constructed on the basis of carefully considering the noise characteristics and ambiguity wavelength of GPS/Galileo/Beidou-3 multi-frequency observations,which achieves the instantaneous positioning accuracy of plane decimeter level and partial moment centimeter level without atmospheric constraints.The enhancement effect of the new frequency points of Beidou-3 B1C/B2 a and Galileo E6 on the instantaneous PPP-AR positioning performance is verified and discussed.Compared with the traditional Galileo E1/E5a/E5 b frequency points,the addition of the new frequency point E6 can improve the combined wide lane ambiguity wavelength and reduce the noise of the observation value.When the satellite altitude angle is low,the instantaneous fixed rate of the wide lane ambiguity increases by about 7%.When the number of satellites is small and the geometric configuration is poor,the positioning accuracy of the instantaneous PPP-AR is in the east The north and zenith directions increased by about 29.62%,42.85% and 8.6% respectively.In general,if the multi-frequency and multi-system GNSS receiver can track Beidou-3 B1C/B2a/B3 I and Galileo E1/E5a/E6 frequency points,these two groups of frequency points should be used as much as possible to improve the performance of instantaneous PPP-AR positioning. |
