# Position Accuracy Improvement by Implementing the DGNSS-CP Algorithm in Smartphones
## 4 Experiments and Results
### Dynamic Test  
In a dynamic test, it is difficult to apply a heavy filter. Thus, a live performance comparison was conducted using a vehicle. An experiment using the S5 was conducted on 20 October 2015, from 20:20 to 20:30, and a test using the V10 was performed on 3 May 2016, from 01:35 to 02:00, when the ionospheric variation is relatively low. It was expected that any improvement in performance would be less pronounced than in the static test. The baseline from the RS was about 250 m, as shown in Figure 12, and the vehicle traveled around a playground at a velocity of approximately 20 km/h. Figure 11: Zero-baseline static test results of the V10 (**(a)** Horizontal error; **(b)** Vertical error). Figure 12: Dynamic Test Setup. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multicolumn{2}{c}{**Statistical Results**} & **Max** & **Mean** & **STD** & **RMS** & **95\%** \\ \hline \multirow{3}{*}{Galaxy S5} & \multirow{2}{*}{Stand-alone} & Horizontal & 1.84 & 1.19 & 0.65 & 1.35 & 1.83 \\  & & Vertical & 4.83 & \(-\)4.36 & 0.42 & 4.36 & 4.83 \\ \cline{2-7}  & \multirow{2}{*}{DGNSS-CP} & Horizontal & 2.04 & 0.41 & 0.69 & 0.80 & 1.85 \\  & & Vertical & 3.76 & \(-\)0.42 & 1.45 & 1.27 & 2.70 \\ \hline \multirow{3}{*}{LG V10} & \multirow{2}{*}{Stand-alone} & Horizontal & 3.69 & 2.83 & 0.88 & 2.96 & 3.78 \\  & & Vertical & 3.45 & 2.30 & 0.60 & 2.28 & 3.17 \\ \cline{2-7}  & \multirow{2}{*}{DGNSS-CP} & Horizontal & 2.13 & 0.73 & 0.93 & 1.19 & 2.08 \\ \cline{1-1}  & & Vertical & 3.3 & 0.20 & 1.38 & 1.25 & 2.44 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistics of Static Test Results. A smartphone was placed on the roof of the vehicle, as shown in Figure 13, and the virtual reference station (VRS) service was applied to the Novatel FlexPak 6 receiver to obtain cm-level positioning; this was regarded as the true position (\(\overset{\rightarrow}{X}_{VRS}\)) of the vehicle. The smartphone was placed 20 cm behind the antenna of the receiver. Thus, its location (\(\overset{\rightarrow}{X}_{smartphone}\)) could be estimated using the velocity (\(\overset{\rightarrow}{V}_{VRS}\)) of the vehicle and the horizontal difference (\(b\)) between the smartphone and the true position. This estimation process is described in Equation (10):  
\[\overset{\rightarrow}{X}_{smartphone}=\overset{\rightarrow}{X}_{VRS}-b\, \frac{\overset{\rightarrow}{V}_{VRS}}{\left|\overset{\rightarrow}{V}_{VRS} \right|} \tag{10}\]  
According to the horizontal results shown in Figure 14, there was a considerable overlap between the VRS (blue) trajectory, which is assumed to be the true position, and the DGPS-CP result from the application (green). However, the standalone result was tilted slightly in a southwest direction. The vertical results confirm that the bias in the DGPS-CP position is smaller than that of the standalone device. The error components in Figure 14 are depicted in Figure 15. As previously identified, the standalone horizontal result exhibits an offset of approximately 2.8 m, whereas the bias of the corrected position has been reduced to 1.2 m. The resulting RMS of the horizontal error has decreased from 3.1 m to 1.9 m. The maximum error of 6.2 m has been reduced to 4.9 m after applying the DGNSS-CP algorithm, and the 2.8 m biased errors of the S5 have decreased to almost zero, only 1.38 m apart from the true position. Figure 14: Trajectory of the dynamic test ((**a**) Horizontal trajectory; (**b**) Vertical trajectory). Figure 13: Configuration of the Automobile in the Dynamic Test ((**a**) Side view; (**b**) Top view). of running third-party applications, and multi-GNSS module enable improved location performance in smartphones by implementing DGNSS functionality. Previous studies have attempted to shift the already-calculated coordinates using the RS real-time position, but they cannot guarantee position accuracies of 2-3 m in smartphones because of the disagreement between the satellite sets of the user and the RS. This paper proposed and implemented a DGNSS-correction projection method for commercial smartphones.