| With the popularization of smartphones and the evolution of Global Navigation Satellite Systems technology,navigation contributes as an indispensable function for smartphones,and more than one half applications require location information permissions.Considering the increasing use of wearable devices and smartphones,the demand of high-precision positioning for mass-market smartphones is becoming higher.From 2016,developers can obtain GNSS raw observations such as pseudorange,carrier phase,doppler through Google Android API(Application Programming Interface)in real time,and the system versions,Android 9.0 and above,provide the option to turn off the duty cycle,which makes it possible for smartphones to conduct Precise Point Positioning(PPP)with valid pseudorange and carrier phase observations.In addition,with the fast hardware turnover on smartphones,more and more phones are equipped with dual-frequency or even tri-frequency GNSS chipsets,the effects of ionospheric delay can be removed by the linear combination of observations from different frequency,which means the improvement of positioning accuracy.However,the widely-used smartphones often use low-cost linearly-polarized antennas,and in urban complex scenarios,the GNSS data they collect have more gross errors,cycle slips and multipath effects.Therefore,the data processing experience of high-quality receivers is not completely suitable for the low-cost smartphone chipset.This article conducts a comprehensive and detailed quality analysis of the observation data for several common-used dual-frequency smartphones,Huawei Mate20/30 and Xiaomi 8,and provides a set of quality control schemes that is suitable for smartphone PPP.At the same time,a real-time PPP application based on the Android platform is developed on the basis of the quality control aid PPP algorithm.Finally,the proposed quality control scheme is verified through the data collected from different scenarios,and the positioning performance of smartphone PPP is analyzed.The main work and conclusions of this article are as follows:(1)With the observation data of the smartphones in different scenarios,signal-tonoise ratio,single-difference pseudorange residual,and carrier phase noise are analyzed.It is found that the pseudorange quality of Xiaomi 8 and Mate 20 are similar,while the carrier phase quality of Mate 20/30 is significantly worse than Xiaomi 8.(2)According to the observations characteristic of smartphone,a combined method of cycle slip detection which is suitable for smart phones is proposed,and then the corresponding PPP quality control schemes was provided.Furthermore,by analyzing the ADRS(Accumulated Delta Range State)identifiers of different smartphones,it is found that the ADRS identifier of Xiaomi 8 can better identify the cycle slip of the phase observations,while it is difficult for Mate 20/30 to directly determine the cycle slips of their observations through the ADRS identifier.Therefore,the Time Difference Carrier Phase method is used to further detect the missed cycle slips.Result shows that smartphones can easily detect multidimensional cycle slips by using the proposed cycle slip detection method.Moreover,a set of PPP quality control schemes and the corresponding thresholds are provided.(3)Basis on the quality control aid PPP algorithm,a real-time PPP Android application is developed.In addition,the user interface is designed and developed based on the Java language,and the technical realization of acquiring and generating Android raw observations,receiving the data stream of State Space Representation,and JNI(Java Native Interface)programming is introduced.(4)By using the smartphone data in different scenarios,the proposed quality control schemes are verified.Results show that by using the proposed quality schemes,the positioning accuracy of SPP and PPP of smartphones has been improved.Moreover,the proposed combined method of cycle slip detection can help the detection of missed cycle slip which the ADRS identifier in Xiaomi 8 fails to detect.In addition,because the ADRS identifier of Huawei Mate 20 can hardly detect cycle slip,this method can be a great help in cycle detection for Huawei Mate 20/30.(5)The positioning performance of SF-PPP versus DF-PPP,real-time PPP versus post-processing PPP of smartphones is comprehensively analyzed.Results show that the positioning errors of Xiaomi 8 in three directions are 0.38 m,0.28 m,0.18 m,respectively,which the accuracy is slightly higher than that of SF-PPP.The DF-PPP of smartphones has great potential,but at present,it is mainly limited by the number of observations,which makes it difficult to be applied in complex urban scenarios.For the smartphones SF-PPP,the difference in horizontal positioning accuracy caused by the use of real-time and post-processing products is about 0.1m,and in the elevation direction,the positioning accuracy of real-time products is worse,which is mainly determined by the accuracy of the ionospheric map products.In general,by employing the quality control aid PPP algorithm,smartphones can achieve an positioning accuracy of 0.5-0.7m and 1.5-2m in static and dynamic scenarios respectively. |
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