# Adaptive Navigation Based on Multi-Agent Received Signal Quality Monitoring Algorithm
## 4 Results and Discussion
However, in complex (severe urban) environments, we have achieved the maximum number of satellites, but there is significant deterioration in the PDOP and position error due to MP/NLOS reception, which disrupts the navigation signals. We can say that the major limiting factor to precise and accurate navigation is the degraded signal quality, not the number of satellites. In order to deeply understand the anomalies in the performance of GNSS, experiments have been carried out in static mode at three different sites, i.e., clear open sky, partially degraded and severely degraded. The observation window for all three candidate sites is 06:00 to 12:00 h. Figure 10a shows the satellite availability, which is quantified by visible satellites and satellite continuity, composed of tracking and outages. In the clear open sky site, we observed that the number of satellites varied from 32 to 43. The mean number of visible satellites is 38, and satellite continuity is estimated to be in tracking without any outages during the entire period. In the second environment, the number of visible satellites moderately degrades; therefore, 24 satellites on average are tracked, and satellite continuity becomes 100%, resulting in complete tracking over the entire time period. Even in the severely degraded environment, we noted the maximum achievable satellites for positioning estimation and observed minimal outages and continuous satellite tracking, resulting in no blockage. Hence, we can say that in all three scenarios, the current developments and technological advancements in the emerging navigation systems have effectively tackled the confined satellite availability in the MP/NLOS conditions, which can be seen in Figure 10a. To quantify the error, PDOP is plotted in Figure 10b for all three sites. PDOP values deviate below 1 during the complete observation window of six hours at the clear open sky site. However, in the moderately degraded case, PDOP rises above 2 and fluctuates between 1 and 2 during the entire observation time. In the case of the severely degraded scenario, there are significant deviations showing some higher peaks in PDOP. On average, PDOP is 7.66, which is a much higher value. We can say that PDOP is greatly disturbed in the degraded and severely degraded cases due to MP/NLOS. As in the degraded and severely degraded sites, adequate numbers of satellites are being tracked, but a large amount of PDOP is still seen, which is due to the reduced signal quality. Signals are highly obstructed in these environments because of complicated surrounding building structure, resulting in limited navigation performance. Figure 10c shows the statistical accuracy for all three candidate sites. The results show that accuracy is highly influenced by MP effects in the severely degraded environment, and the more the signal is obstructed, the worse the accuracy achieved. The clear open sky proves to be the best-case scenario, as Circular Error Probable (CEP) and Distance Root Mean Square (DRMS) were found to be 0.8 and 0.96 due to no obstructions. In the moderately degraded case, the radii of accuracy measures of CEP and DRMS are estimated as 3.2 and 4.4, respectively. In the case of the severely degraded site, CEP and DRMS are increased to 13.1 and 15.7, respectively. The statistics is given in Table 3.  
It can be observed that positioning uncertainty increased by 2 times due to MP/NLOS reception. Hence, it is observed that MP/NLOS represent the major error sources for navigation performance, as it increases the error, which leads to inaccurate positional accuracy. The performance evaluation of the positioning and navigation under multi-constellation GNSS mode signifies that in highly urbanized environments, navigation performance is greatly challenged and vulnerable to multi-paths and NLOS. It is essential to take countermeasures to reduce the positioning error.