GNSS Data Quality Assessment And Positioning Performance Analysis Of Android Smartphone

With the development of Global Navigation Satellite System(GNSS),location services based on smartphones and other terminals are becoming increasingly widespread.And the field is gradually expanding to include pedestrian navigation,location crowdsourcing and precision marketing.People’s demand for the positioning accuracy of smartphones is increasing.However,smartphones are equipped with low-cost chips and linear polarization antennas,their GNSS observation data quality is poor,resulting in poor positioning effect.The research on highprecision positioning technology based on Android smartphone GNSS observations has become international research hotspots.With the comprehensive completion of China’s Beidou Navigation Satellite System,the addition of new frequency points will also greatly enhance the positioning performance of Android smartphones.This paper firstly conducted research on the raw observation data of smartphones,and evaluated the data quality of multiple mainstream Android smartphones in the domestic market from multiple perspectives.Subsequently,on the basis of studying the multipath error model of tri frequency signal of BDS,this paper evaluated the data quality of tri frequency signal of BDS on smartphones.Finally,the positioning performance of smartphones in different environments was analyzed.Based on the characteristics of Android data,the existing GNSS positioning algorithm has been improved.The main research work and achievements are as follows:(1)Aiming at the research and analysis on the quality of GNSS raw observation data for smartphones are not comprehensive,this paper investigated the method of obtaining raw GNSS observations.Designed static and dynamic experiments to collect GNSS raw observation data,and evaluated GNSS data quality of Android smartphones from multiple aspects such as integrity rate,cycle slip rate,signal-to-noise ratio(SNR),multipath error and so on.The experimental results indicate that: There are differences in GNSS data quality levels among different models of Android smartphones.And not all dual band smartphones have better data quality than single band smartphones.The placement and stability of smartphones can also have a certain impact on data quality.Even if the same model of smartphones are placed in the same observation environment,there are still significant differences in the results of data quality indicators.(2)Aiming at the problem that the multipath effect accounts for a large proportion of smartphones positioning error sources,this paper studied the multipath error model of tri frequency signal of BDS,and analyzed the data quality of the new frequency point signal of BDS.The experimental results indicate that: The B1C/B2 a new frequency point of BDS3 has advantages,resulting in an overall improvement in data quality level.The integrity rate and signal-to-noise ratio of the B1 C and B2 a on MEGX station are close.The signal-to-noise ratio of B2 a is higher than all frequency points except GPS L2.And the multipath error of B1 C and B2 a is less than the B1 I.Android smartphones have significantly stronger ability to capture BDS satellite signals than GPS satellite.The geometric distribution of satellites observed by smartphones is good,and the accuracy factor values are all below 3.The average integrity rate at each frequency point is greater than 90%.The multipath error of B1 C is lower than other frequency points.Both B1 C and B2 a have better noise resistance than B1 I.(3)Aiming at the problem that the GNSS observation data quality of smartphones is unstable.Studied the technology for data preprocessing and quality control,and designed and implemented methods for carrier phase and Doppler smoothing pseudorange on smartphones.The single-point positioning accuracy based on carrier phase and Doppler smoothing pseudorange respectively reaches 1.34 m,1.57 m,2.72 m and 0.86 m,0.97 m,1.53 m in E,N,and U directions.Matched with the unsmoothed data,the positioning accuracy is improved by 61.38%,58.68%,49.44% and 75.22%,74.47%,71.56%.Studied and analyzed the RTK positioning performance of multiple smartphones under different observation conditions.The experimental results indicate that: The positioning errors of Android smartphones in the E,N,and U directions reached 0.48 m,0.60 m,and 2.50 m.Although there is a gap with the results of geodetic receivers,the most of smartphones can achieve positioning accuracy of decimeters in the horizontal direction and meters in the elevation direction.This provides a low-cost solution for people’s higher precision positioning needs in urban life.