## 4 Discussion  
This study investigated the static GNSS positioning accuracy of novel multi-frequency multi-constellation smartphones and compared them with single-frequency and geode  
Figure 10: Boxplot of the absolute position error of the different receivers. Blue indicates smartphones that have multi-frequency capabilities, and red indicates smartphones that can only receive the L1/G1/E1/Bll bands. \begin{table}
\begin{tabular}{r c c c c c c c c c} \hline \hline  & **Geo 7X** & **Mi 8** & **MI 8P** & **MI 10** & **P20** & **P40** & **A7** & **S5** & **XC4 sa** & **XC4 sb** \\ \hline Xiaomi Mi 8 & 0.00 & & & & & & & & \\ Xiaomi Mi 8 Pro & 0.00 & 0.00 & & & & & & & \\ Xiaomi Mi 10 light & 0.00 & 0.00 & 0.00 & & & & & & \\ Huawei P20 & 0.00 & 0.00 & 0.00 & 0.00 & & & & & \\ Huawei P40 & 0.00 & 0.00 & 0.88 & 0.00 & 0.00 & & & & \\ Samsung A7 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & & & \\ Samsung S5 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & & \\ Samsung Xcover 4s\_a & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & \\ Samsung Xcover 4s\_b & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & \\ Samsung Xcover 4 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 & 0.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Wilcoxon Rank Sum Test with continuity correction and ’holm’ correction between the absolute positioning errors of the studied smartphones (\(p\)-values, \(\alpha=0.05\)). tic receivers under forest conditions. The acquisition of detailed and spatially accurate positioning data is required in several forest business applications. It can be assumed that the data provided by multi-constellation, dual-frequency smartphone receivers can reach a higher GNSS accuracy under a forest canopy based on the increase in the signal availability and the elimination of ionospheric error. Under open sky conditions and special GNSS raw data analyses, such as carrier phase observations, after successful ambiguity fixation, centimeter-level accurate positioning with multi-frequencies smartphones is possible [59; 70; 78; 88]. The current study has focused on the position solution that smartphones deliver directly and in difficult conditions in a forest. Further studies show that the accuracy for point measurements under open area conditions are between two and six times higher compared to point measurements under forest conditions [89]. The reception qualities vary considerably between the different reception conditions (study sites). It is challenging to quantify the environmental conditions under the canopy of a forest that influences reception [21], and available methods, such as free-sky classification, are only conditionally suitable for describing a correlation with position accuracy [16]. Therefore, it is difficult to generalise the results of different GNSS studies under forest conditions. This is particularly true for smartphones as receivers, as even smartphones of the same design deliver different positions to the same reception conditions under a canopy. Even the number of satellites in use alone cannot be considered reliable for estimating position accuracy. Other studies have also come to this conclusion [70]. In static GNSS accuracy studies, the question of how long or how many fixed points should be recorded is always addressed during the experiment setup. The duration of the GNSS recording under a forest canopy has a significant influence on the absolute error and the precision [90; 91], and a longer averaging of position values can usually improve it significantly [92; 61; 90]. In the present study, a recording of at least 10 min with an recording interval of 1 Hz was made at each position. The chosen (optimal) recording time for the experimental determination of static positions has been evaluated differently by different authors and ranges from 2 to 120 min [92; 28; 93; 94; 95; 27]. However, even 2 min of waiting time for GNSS positioning with a smartphone is too long in practice, as working people usually do not want to wait long for a more accurate position.