Performance Analysis of Smart-phone Measurements based Positioning with External Corrections

Vijaykumar Bellad and Thyagaraja Marathe

Abstract: Today, several Android devices provide access to raw GNSS measurements. This has not only rendered a developmental framework for various applications but also opened up new research avenues. With an increasing number of smart-phone chip manufacturers providing raw GNSS measurements, one would expect to see an increase in use cases and applications that utilize this data to enhance position accuracy. Previous research on smart-phone based measurements (a.k.a. observations; here, two terms used interchangeably) has explained the way of accessing measurements from Android phones and has presented preliminary assessment of data quality and the positioning performance that can be obtained with observations collected by a smart-phone (Banville & van Diggelen, 2016). Position performance for observations from different devices was compared in the laboratory environment by Riley, et al. (2018). Furthermore, potential use of these observations for RTK positioning was studied by collecting observations over multiple frequencies; the challenges that can be encountered in the practical implementation were highlighted. In another work, effects of carrier smoothing of pseudorange measurements and use of differential corrections on smart-phone measurements were presented (Shin, et al., 2017) Position improvement methods investigated in previous works mainly focussed on smoothing pseudorange measurements, use of differential corrections and multiple frequency observations for stationary use cases. Application of external corrections to improve the quality of pseudorange based user positioning for static and kinematic user scenarios is less explored. User position accuracy in GNSS receivers depends on the accuracy of range measurements to the satellites. The major range error sources in GNSS receivers include satellite orbit and clock errors, ionospheric and tropospheric delay modeling errors, multipath, and receiver noise. For generic user scenarios, multipath and receiver noise cannot be modelled unlike other errors. Normally, smart-phone receivers rely on broadcast satellite data for orbit determination, satellite clock corrections’ and ionospheric delay computation. Although broadcasted satellite orbit, clock and ionospheric delay parameters provide reasonably good accuracy, new navigation applications demand higher accuracy. In the present work, it is proposed to use precise orbits, clocks and external ionospheric corrections to further improve positioning accuracy. Standard single frequency receivers can have significant ionospheric correction errors due to limitations of the standard model. In the present work ionospheric corrections are computed using a global ionospheric model derived using multi-frequency observations from a global network of GNSS receivers. For initial evaluations, static data was collected using an automotive grade receiver with a directional antenna and a smart-phone. Use of precise satellite orbits, clocks and external ionosphere corrections with automotive grade receiver yielded improved position accuracy. A similar performance improvement is anticipated with measurements from the smart-phone. Ongoing and future work focuses on assessing results from different static and kinematic data sets. Additionally, effect of the performance of antenna on the user position estimation will be explored. Results from the above analyses will be included in the publication. References: Banville, S., & van Diggelen, F. (2016, November 07). Precise GNSS for Everyone: Precise Positioning Using Raw GPS Measurements from Android Smartphones. GPS World 27(11), pp. 43-48. Retrieved from European GNSS Agency. (2017). Using GNSS Raw Measurements on Android Devices - Towards better location performance in mass market applications. Luxembourg: Publications Office of the European Union. doi:10.2878/449581 Riley, S., Landau, H., Gomez, V., Mishukova, N., Lentz, W., & Clare, A. (2018, January 17). Positioning with Android: GNSS observables. GPS World. Retrieved from Shin, D., Lim, C., Park, B., Yun, Y., Kim, E., & Kee, C. (2017). Single-frequency Divergence-free Hatch Filter for the Android N GNSS Raw Measurements. Institute of Navigation GNSS+ 2017 (pp. 1-38). Portland: The US Institute of Navigation.
Published in: Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018)
September 24 - 28, 2018
Hyatt Regency Miami
Miami, Florida
Pages: 413 - 431
Cite this article: Bellad, Vijaykumar, Marathe, Thyagaraja, "Performance Analysis of Smart-phone Measurements based Positioning with External Corrections," Proceedings of the 31st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2018), Miami, Florida, September 2018, pp. 413-431.
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