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. 2021 Dec 13;21(24):8318.
doi: 10.3390/s21248318.

Instantaneous, Dual-Frequency, Multi-GNSS Precise RTK Positioning Using Google Pixel 4 and Samsung Galaxy S20 Smartphones for Zero and Short Baselines

Chien Zheng Yong  1   2 , Robert Odolinski  1 , Safoora Zaminpardaz  3 , Michael Moore  4 , Eldar Rubinov  5 , Jeremiah Er  1 , Mike Denham  1
Affiliations

Instantaneous, Dual-Frequency, Multi-GNSS Precise RTK Positioning Using Google Pixel 4 and Samsung Galaxy S20 Smartphones for Zero and Short Baselines

Chien Zheng Yong et al. Sensors (Basel). .

Abstract

The recent development of the smartphone Global Navigation Satellite System (GNSS) chipsets, such as Broadcom BCM47755 and Qualcomm Snapdragon 855 embedded, makes instantaneous and cm level real-time kinematic (RTK) positioning possible with Android-based smartphones. In this contribution we investigate the instantaneous single-baseline RTK performance of Samsung Galaxy S20 and Google Pixel 4 (GP4) smartphones with such chipsets, while making use of dual-frequency L1 + L5 Global Positioning System (GPS), E1 + E5a Galileo, L1 + L5 Quasi-Zenith Satellite System (QZSS) and B1 BeiDou Navigation Satellite System (BDS) code and phase observations in Dunedin, New Zealand. The effects of locating the smartphones in an upright and lying down position were evaluated, and we show that the choice of smartphone configuration can affect the positioning performance even in a zero-baseline setup. In particular, we found non-zero mean and linear trends in the double-differenced carrier-phase residuals for one of the smartphone models when lying down, which become absent when in an upright position. This implies that the two assessed smartphones have different antenna gain pattern and antenna sensitivity to interferences. Finally, we demonstrate, for the first time, a near hundred percent (98.7% to 99.9%) instantaneous RTK integer least-squares success rate for one of the smartphone models and cm level positioning precision while using short-baseline experiments with internal and external antennas, respectively.

Keywords: dual frequency; multi-GNSS; real-time kinematic (RTK); smartphone positioning.

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Conflict of interest statement

The authors declare that there is no conflict of interest.

Figures

Figure 1
Figure 1
General external antenna setup configuration of S20 and GP4 smartphones that will be benchmarked against survey-grade Trimble NetR9 and low-cost ublox receivers/antennas. All receivers/antennas are placed in a RF shielding box to prevent them from receiving GNSS signals that are not from the re-radiating antenna. The direct GNSS signals are collected from the active low-cost antenna on the rooftop, Swift GPS500, and re-radiated via a passive antenna. A signal amplifier is connected in between the rooftop antenna and re-radiating antenna to reduce the effect of signal attenuation. Inset (right column) depicts the location map of Dunedin, New Zealand.
Figure 2
Figure 2
Zero-baseline setup configurations for smartphones in (a) upright and (b) lying down positions. The re-radiating antenna receives the GNSS signals through the roof-top antenna in Figure 1.
Figure 3
Figure 3
Short-baseline setup configurations with external antennas (c,f) in upright (a,d) and lying down (b,e) positions.
Figure 4
Figure 4
Short-baseline setup configurations with smartphones internal antennas in upright (a,b) and lying down (c,d) positions.
Figure 5
Figure 5
Zero baseline with smartphones in a (a) lying down and (b) upright position (cf. Figure 2): Horizontal (N, E) positioning scatter (first row) and corresponding vertical (U) positioning error time-series (second row) for 12 h of data (cf. Table 2) with GP4 (left column) and S20 (right column). In this RTK model GPS + Galileo + QZSS +BDS L1 + L5, E1 + E5a, L1 + L5, B1 observations have been used. A zoom-in window is shown to depict the two orders of magnitude when going from incorrectly fixed (red dots) and ambiguity-float (gray dots), to correctly fixed solutions (green dots). The 95% empirical and formal CIs and ellipses for the correctly fixed solutions are shown as blue and red lines, respectively. The number of visible satellites and the correctly fixed formal up STDs (bottom row) are shown as black and green lines, respectively. The black dashed lines indicate the zoom-in period between epoch 13,800 and 25,000, see further Figure 7, with ILS SRs of 99.9% in both (a,b) in the left column for GP4 and 31.0% in (a) and 97.4% in (b) in the right column for S20, respectively. (a) Smartphones used in lying down positions: with GP4 (left): ILS SR 99.9% and S20 (right column): 79.4%. (b) Smartphones used in upright positions: with GP4 (left): ILS SR 99.9% and S20 (right column): 97.8%.
Figure 6
Figure 6
Zero baseline with smartphones in a (a) lying down and (b) upright position (cf. Figure 2): North error histograms (green bars) together with their empirical (blue lines) and formal (red lines) PDFs, with GP4 in the left column and S20 in the right column. (a) Smartphones used in lying down positions: with GP4 (left) and S20 (right column) using an external antenna. (b) Smartphones used in upright positions: with GP4 (left) and S20 (right column) using an external antenna.
Figure 7
Figure 7
Zero baseline withS20 in (a) and GP4 in (b), both in a lying down (left column) and upright position (right column): the DD phase residual time series of the L1 signal (top row) is shown for epoch 13,800 and 25,000 (cf. dashed black lines in Figure 5). The DD phase residuals of GPS are depicted as blue dots and QZSS as cyan dots. The black dashed lines indicate the zoom-in period of the L1 DD phase residuals (bottom row) between the epochs 19,800 and 23,400. (a) S20 smartphones used in the lying down position (left) and upright position (right column) using an external antenna. (b) GP4 smartphones used in the lying down position (left) and upright position (right column) using an external antenna.
Figure 8
Figure 8
Short baseline withS20 in (a) and GP4 in (b) using external antennas (cf. Table 2) in lying down (left column) and upright position (right column): The DD phase residuals for 1 h of data of L1 GPS are depicted as blue, E1 Galileo as green and L1 QZSS as cyan dots. Note that there was only one QZSS satellite in the GP4 dataset in (b) and the left column, and thus the corresponding DD phase residuals were not depicted. (a) S20 smartphones used in the lying down position (left) and upright position (right column) using external antennas. (b) GP4 smartphones used in the lying down position (left) and upright position (right column) using external antennas.
Figure 9
Figure 9
Short-baseline with external antennas and smartphones in an upright position (cf. Figure 3): Horizontal (N, E) positioning scatter (first row) and corresponding vertical (U) positioning error time-series (second row) for 8 h of data (cf. Table 2) with GP4 (left column): ILS SR 99.9% and S20 (right column): 99.2%. In this RTK model GPS + Galileo + QZSS + BDS L1 + L5, E1 + E5a, L1 + L5, B1 observations have been used. A zoom-in window is shown to depict the two order of magnitude improvement when going from incorrectly fixed (red dots) and ambiguity-float (grey dots), to correctly fixed solutions (green dots). The 95% empirical and formal confidence CIs and ellipses for the correctly fixed solutions are shown as blue and red lines, respectively. The number of visible satellites and the correctly fixed formal up STDs (bottom row) are shown as black and green lines, respectively.
Figure 10
Figure 10
Short-baseline with internal antennas and smartphones in a (a) lying down and (b) upright position (cf. Figure 4): Horizontal (N, E) positioning scatter (first row) and corresponding vertical (U) positioning error time-series (second row) for 3.5 h of data (cf. Table 2) with GP4 (left column) and S20 (right column). In all RTK models GPS + Galileo + QZSS + BDS L1 + L5, E1 + E5a, L1 + L5, B1 observations have been used for GP4, except for S20 in (b) that did not have more than one QZSS satellite to formulate the DD observations. A zoom-in window is shown to depict the two order of magnitude improvement when going from incorrectly fixed (red dots) and ambiguity-float (grey dots), to correctly fixed solutions (green dots). The 95% empirical and formal CIs and ellipses for the correctly fixed solutions are shown as blue and red lines, respectively. The number of visible satellites and the correctly fixed formal Up STDs (bottom row) are shown as black and green lines, respectively. (a) Smartphones used in lying down positions: with GP4 (left): ILS SR 63.1% and S20 (right column): 27.5% (internal antennas). (b) Smartphones used in upright positions: with GP4 (left): ILS SR 98.7% and S20 (right column): 64.4% (internal antennas).
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