# Adaptive Navigation Based on Multi-Agent Received Signal Quality Monitoring Algorithm
## 4 Results and Discussion
The quality of signals is highly influenced by these rapidly changing environments and GNSS signal characteristics remarkably deviate from their standard values, resulting in unreliable and inaccurate PNT solutions. These GNSS signal characteristics are quantified by carrier-to-noise ratio (CNR), code-carrier divergence (CCD) and range residuals (RR). Figure 11 shows the detailed analysis of satellite signal characteristics in three different scenarios/environments. Figure 11 (a) represents the carrier-to-noise ratio (CNR) (dB-Hz), (b) is the code-carrier divergence (CCD) (m)and (c) shows the normalized range residuals (RR) (m) for three satellites chosen in each environment. It is observed that in the clear open sky environment, all three satellites follow a similar pattern, and minimal variations were found in CNR, CCD and RR. Most of the time, CNR fluctuates above 35 dB-Hz, and CCD varies between 0 and 1, which results in RR being reduced to \(-1\). When the environment changes from a clear open sky to a moderately degraded environment, it is clearly observed that there is an increase in the CNR variations. PRN:R02 fluctuates below 40 dB and drops to less than 30 dB at some intervals. PRN:E24 also deviates below 40 dB during the complete lock time. Similar performance can be seen in CCD, which is increased up to 6 m, and RR deviates between \(-10\) m and 20 m. It is observed that in a moderately degraded environment, some of the measurements are affected by the surroundings, i.e., complex building structures, and MP remains the most prominent source of positioning uncertainties in these cases. The severely degraded environment is the worst case scenario, having strong multi-paths and NLOS effects. It is depicted in Figure 11 that there are significant deviations in GNSS signal parameters (CNR, CCD and RR). CNR drops to 35 dB and all three satellites exhibit variation in an irregular manner. CCD increased to 4m and some peaks were found at 6 m. It is observed that RR rises to 20 m, and contingent deviation is found in RR during the complete lock time of satellites. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Observation** & **Constellation** & **Satellite Availability** & **PDOP** & **Position Error** & **Accuracy** \\
**Condition** & & **Max/Avg/Min** & **Max/Avg/Min** & **Max/Avg/Min** & **CEP (m)** \\ \hline \multirow{4}{*}{Stationary} & GNSS & 43/39/32 & 0.92/0.79/0.71 & 1.35/0.96/0.71 & 0.8042 \\  & (Open Sky) & & & & \\ GPS & \(11/09/08\) & 2.25/1.68/1.39 & 1.49/1.33/1.13 & 1.0877 \\  & (Open Sky) & & & & \\ GNSS & \(30/24/20\) & 2.24/1.77/1.23 & 6.40/3.46/1.34 & 3.2044 \\  & (MP) & & & & \\ \hline \multirow{2}{*}{Moving} & GNSS & 35/27/15 & 2.00/1.21/0.80 & 6.84/2.57/0.96 & 2.2589 \\  & GPS & 10/08/04 & 9.65/2.58/1.78 & 14.9/4.41/5.95 & 4.5877 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Multi-constellation GNSS Data Statistics in each candidate sites. Figure 10: Positioning performance comparison of multi-constellation GNSS. In order to further quantify the GNSS signal parameters, the histograms of CNR, CCD, and RR are plotted, as shown in Figures 12-14. It shows that the distributions of measurements follow the different patterns due to environmental changes. As expected, most of the CNR values are above 35 (dB-Hz) in the clear open sky environment, with most of the LOS components. Figure 12a shows that the total number of occurrences is 200, of which 140 values lie between 35 and 50 (dB-Hz). Due to the environmental changes, the received signal comprises multi-path, LOS and NLOS, which results in reduced CNR. This is depicted in Figure 12b,c. The main portion of CNR is achieved in the range of 20 to 30 (dB-Hz) in the degraded environment. CNR becomes worst in the highly degraded environment, and most of the CNR values lie below 30 (dB-Hz), indicating a higher number of NLOS and multi-path components in the received signal. The histogram of CCD is given in Figure 13a-c under different environments.