# A Combined Elevation Angle and C/N0 Weighting Method for GNSS PPP on Xiaomi MI8 Smartphones
###### Abstract  
Traditionally, an elevation-angle-dependent weighting method is usually used for Global Navigation Satellite System (GNSS) positioning with a geodetic receiver. As smartphones adopt linearly polarized antenna and low-cost GNSS chips, different GNSS observation properties are exhibited. As a result, a carrier-to-noise ratio (C/N0)-dependent weighting method is mostly used for smartphone-based GNSS positioning. However, the C/N0 is subject to the effects of the observation environment, resulting in an unstable observation weight. In this study, we propose a combined elevation angle and C/N0 weighting method for smartphone-based GNSS precise point positioning (PPP) by normalizing the C/N0-derived variances to the scale of the elevation-angle-derived variances. The proposed weighting method is validated in two kinematic PPP tests with different satellite visibility conditions. Compared with the elevation-angle-only and C/N0-only weighting methods, the combined weighting method can effectively enhance the smartphone-based PPP accuracy in a three-dimensional position by 22.7% and 24.2% in an open-sky area, and by 52.0% and 26.0% in a constrained visibility area, respectively.  
GNSS; smartphone; precise point positioning; elevation angle; C/N0 +
Footnote †: journal: Sensors  
0000-0002-4000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000-0000  
respectively. Nevertheless, the positioning accuracy decreased to 3-4 m in the kinematic mode due to insufficient dual-frequency observations. In addition, using the Xiaomi MI8 smartphone, [PERSON] and [PERSON] [11] utilized the C/N0-dependent stochastic model to improve the static PPP three-dimensional (3D) accuracy by about 27.0% over the elevation-angle-dependent stochastic model. [PERSON] et al. [12] used a Huawei Mate 30 smartphone to test the PPP in a kinematic mode based on the C/N0-dependent stochastic model to achieve a positioning accuracy of 0.93 m, 0.62 m and 2.17 m in the east, north and up directions, respectively; the accuracy was improved by about 26.2%, 20.5% and 20.4% when compared with the elevation-angle-dependent stochastic model. From the existing research, the advantage of the C/N0-dependent stochastic model is obvious for smartphone-based GNSS positioning. Although the C/N0-dependent weighting methods are mostly used in the smartphone-based GNSS positioning, the C/N0 is subject to the effects of the observation environment and severely fluctuates in the dynamic process. As a result, the C/N0-derived observation weights are prone to instability. Recently, a combined elevation angle and C/N0 weighting method was applied to smartphone-based kinematic PPP by simply dividing the C/N0-derived variances by the elevation-angle-derived variances. A sub-meter positioning accuracy can be achieved based on the combined weighting method [13]. However, its performance was not compared with the other weighting methods and thus its advantage is unclear.  
In this study, a new combined elevation angle and C/N0 weighting method is proposed for smartphone-based PPP by normalizing the C/N0-derived variances to the scale of the elevation-angle-derived variances. The performance of the proposed weighting method is compared with the elevation-angle-only and C/N0-only weighting methods in two kinematic smartphone-based PPP tests. The paper is outlined as follows: firstly, the correlations among the code multipath and noise (CMN), C/N0 and elevation angle are analyzed; secondly, a combined elevation angle and C/N0 weighting method for the smartphone-based PPP is presented; and finally, the proposed weighting method is evaluated in two kinematic PPP experiments.