## 4 Results Analysis
### Urban Test Case
Additionally noticeable is that fewer outliers appear for GPS and Galileo DDs in the stand still phase of the vehicle, which is the time until the first vertical line labelled with A. Also, the noise is lower in the static phase of the experiment. However, this does not apply to GLONASS DDs. During the repeatedly driven five rounds of the trajectory between labels B\({}_{\text{Start}}\) and B\({}_{\text{End}}\), neither a change in the noise level nor in the appearance of outliers is visible. The noise characteristics of the DD time series are analysed using the Allan deviation (ADEV), which is the square root of the Allan variance [39; 40]. To be more precise, the modified ADEV mod \(\sigma_{y}(\tau)\) is computed as it can distinguish between white phase noise and flicker phase noise. Since the ADEV is computed for continuous time series and this data set includes many data gaps due to signal interruptions, the DD time series from one satellite pair per system, which is almost continuous,  
Figure 8: DDs of L1 carrier phase observations from all satellites for different receiver combinations with respect to GPS time. GPS, GLONASS and Galileo DD are shown in blue, green and red colours, respectively. Black dashed vertical lines indicate different points of the trajectory, which are explained in Table 1.  
is selected for this analysis. The modified ADEV's are depicted in Figure 9a. The corresponding elevation angles for these satellite pairs with respect to GPS time is shown in Figure 9b. The noise level can be obtained at \(\tau=1\) [s]. The modified ADEV supports the statement that the noise level of the DD time series of the UBX combination is higher compared to the JVD combination; this applies to all the systems. At \(\tau=1\) [s], the values for the DDs of the geodetic combination is even below 2 mm. The slope of the respective curves is an indicator for the underlying noise process. For all combinations and signals, a white noise process for the carrier phase DDs with a slope of \(\tau^{-3/2}\) is indicated in the figure for at least the first 100 s.  
In order to carry out the stochastic analyses of the DDs, the computed DDs are investigated with respect to the elevation angles of the non-reference satellites (cf., Figure 10). A clear elevation dependency, which can be expected at least in static experiments, is not visible in any of the combinations and GNSS systems. Especially, the Galileo DDs of the JVD receivers show properties of even higher noise and more outliers for elevations between 30\({}^{\circ}\) and 60\({}^{\circ}\). This is due to the fact that this range of elevations is particularly critical. It is shown in [41; 42] that most of the signal reflections occur in these elevation ranges due to the building heights in the immediate vicinity of the antenna. Since the magnitude of the DD noise is not particularly elevation dependent, the C/N\({}_{0}\) is considered as another measure to characterise the observation quality. The results are depicted in Figure 11. Note that the x-scaling is different for the different receiver combinations. The behaviour of the DD noise with respect to the C/N\({}_{0}\) values of the non-reference satellites highly differs considering one receiver combination with the other. For the geodetic-grade combination (cf. Figure 11a-c) there is a high C/N\({}_{0}\) dependency visible. The DD noise is increasing for low C/N\({}_{0}\)s and is decreasing when the C/N\({}_{0}\)s are increasing. This applies similarly for all three GNSS systems. Note that due to receiver-internal settings, the recording of observations is stopped when the C/N\({}_{0}\) is roughly less than 20 dB-Hz. The behaviour of the DD noise of the UBX receivers with respect to C/N\({}_{0}\) is shown in Figure 11d-f. Note that the resolution of the C/N\({}_{0}\) is only 1 dB-Hz. A clear C/N\({}_{0}\) dependency is hardly visible. The receivers are well-known as high sensitivity equipment as it has the capability of tracking more signals even if the ray is blocked from buildings.