Statistical Characterization of BeiDou Navigation Errors with A Consumer Multi-Constellation GNSS Receiver

C-T. Weng, C-W. Chen, W-H. Ting

Abstract:	BEIDOU system has been commercially operational since the end of 2012, and is currently a constellation of 14 satellites providing positioning, navigation and timing services to the Asia-Pacific region. The open service is free to civilian users with positioning accuracy of 10 m, timing accuracy of 20 ns and velocity accuracy of 0.2 m/s. Beidou will be one of the most important satellite navigation systems to eventually cover the entire globe by 2020. Since the BEIDOU system comprises 5 satellites in GEO, 5 in IGSO and 4 in MEO. The MEO satellites will offer complete global coverage in the future and is similar to the GPS and GLONASS. The IGSO and GEO satellites will not only improve the visibility and availability for users in China and neighboring regions (Eastern Hemisphere), but also provide the backward compatibility with the BEIDOU-1 system. Since the BEIDOU satellites share many common features with GPS and Galileo, however, it is to deserve to be mentioned that BEIDOU is the first system that provide combination solution with three different orbital satellites. Most of the commercial multi-GNSS receiver solutions currently have rapid increase adoption in smartphones, tablets and automotive vehicles which are mostly designed and adjusted with the MEO satellites measurements. Thanks to the rapid progress of the BEIDOU satellite deployment, it provides a good time to review the quality of GEO and IGSO ranging measurements in consumer navigation solution again. This reason motivates us considering a review and investigation of an integrated GNSS solution which can do particularly positioning computed from measurements of these high altitude GNSS satellites. In this paper, a series of quality analysis of BEIDOU measurements including satellite visibility and validity of measurements, carrier-to-noise density ratio and code noise are shown with statistical results. In additional, the error source and the results of navigation data, including position, velocity and timing are then presented and analyzed. In this paper, results of quality analysis using BEIDOU measurements performed by Mediatek MT3333 receivers, the latest all-in-1 multi-GNSS receiver SoC solutions that successfully supporting GPS, BEIDOU, GLONASS, GALILEO, and QZSS constellations, will be presented. Satellite visibility and observation validity will be obtained while GNSS satellites to be above a specified minimum elevation so that the receiver and the tracked satellite have a clear line of sight. Unlike MEO satellites (GPS), the BEIDOU GEO satellites always stay above the equator and IGSO satellites have a ground track of ‘‘figure-8’’ shape with its central longitude being located at about 1188 East. Result of BEIDOU sky plot observed in Taipei/Beijing will be observed in the final paper. The carrier-to-noise density ratio (C/N0) given by a receiver is a result of signal gain and loss along the complete transmitting and receiving chain (Hauschild et al. 2011). The whole chain consists of the electronic circuit and antenna of the satellite, the signal path, and the antenna and the electronic circuit of the receiver. It should be kept in mind that the C/N0 values are not precise measurements as they are just a rough indication of the signal gain and loss. The observations of time series of B1 raw measurements for typical BEIDOU satellites will also be obtained and analyzed. In the standalone BEIDOU solutions, an accuracy of 20 m can be achieved. However, the results showed that BEIDOU may have poorer performance in terms of velocity compared with GPS on the basis of an assumption that BEIDOU orbit have larger noise level from statistical characterization. The analysis result of code and doppler raw measurements combinations shows that the noise level of BEIDOU code measurements is higher than that of GPS collected using the same receiver. This error behavior is then stripped down by error analysis and BEIDOU signal characteristics together with its orbit and clock determination will be adopted. The satellite position and clock model are obtained from the broadcast navigation message, while the clock offset as well. Raw measurements were computed from two GNSS receivers that tracked BEIDOU observations and zero-base line differential method will be then applied to eliminate multipath and the systematic error source. In our early investigation, the doppler measurements are demonstrating unexpectedly high temporal variations. The statistics of the similarity of the code and phase derived solution showed that both types of observations were likely affected by the temporal variations. The variations were probably due to the instability of the onboard clock that may have rapid frequency offset variations or the velocity uncertainty. The analysis data indicates that while the geostationary satellite may remain near a fixed position in the sky, it is not truly stationary. Slight disturbances and perturbations produce small variations of the orbital elements. These cause the inclination and eccentricity to wander from zero. Over time, the perturbations cause the variation of the position from the desired point to grow. This necessitates occasional orbit maneuvers to keep the satellite within the design limits. The BEIDOU’s broadcast ephemeris is frequently updated by every hour, the orbit error have been validated within server hundred meters within the validation period, however, the GEO’s velocity uncertainty is not guaranteed and there still no description of velocity model from the published ICD. Therefore this may contribute the additional navigation velocity errors while using GEO’s doppler measurements in the navigation solution. In the final paper, we will present a quality analysis on measurements of BEIDOU GEO, and IGSO satellites. The positioning and velocity solution of a standalone GNSS receiver using BEIDOU B1 code only and code plus phase measurements are carried out as well as the standalone BEIDOU solutions. The positioning error analysis results are compared with the ‘‘ground truth.’’ This work will also demonstrate a robust solution which overcome the challenge that we mentioned above, and present a neat and reliable GNSS receiver running on a mobile phone.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	2821 - 2827
Cite this article:	Weng, C-T., Chen, C-W., Ting, W-H., "Statistical Characterization of BeiDou Navigation Errors with A Consumer Multi-Constellation GNSS Receiver," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 2821-2827.
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