# Adaptive Navigation Based on Multi-Agent Received Signal Quality Monitoring Algorithm
## 4 Results and Discussion
#### Adaptive Navigation (Mitigation using RSQM)  
Based on the detailed analysis, it is concluded that signal quality is highly influenced by degradation in the environment, like MP/NLOS receptions. To mitigate the effects of MP/NLOS receptions, an adaptive mitigation technique must be adopted to improve the navigation performance. This adaptive positioning and navigation technique exploits the redundancy of range measurements (i.e., increased satellite availability) and selects the optimal signal quality/range measurement position and navigation solution and excludes/masks affected range measurements while considering the satellite geometry constraints. The reported average position error in urban canyon was 2.7 m; this can be further reduced if the affected measurements are discarded and not used in position estimation. As GNSS is advanced with increased satellite availability, having a higher number of satellites, the RSQM algorithm chooses that subset of satellites that are less affected by obstructions and selects the best-quality signals in position measurements to improve the navigation performance. There are several studies that have adopted the masking and exclusion algorithms of faulty measurements for improved positioning performance. Those studies rely  
Figure 14: Histogram and normal distribution of CNR for all the environments (**a**) Clear open sky, (**b**) Degraded Environment and (**c**) Highly degraded environment. Figure 13: Histogram and normal distribution of CCD for all the environments (**a**) Clear open sky, (**b**) Degraded Environment and (**c**) Highly degraded environment. on parameters like CNR, range residuals and elevation angle to exclude the faulty/NLOS measurements using a single constellation. However, in the case of multi-constellation monitoring, each parameter can increase the processing load of the GNSS receiver. Higher CNR values and elevation angles are indicators of the best-quality signals and they are least influenced by obstructions. Taking this into consideration, the RSQM algorithm adopted the adaptive approach to mask the CNR and elevation angle. Table 4 shows the receiver settings according to the detected signal quality in different environments. Figure 15 shows the performance of GNSS in different regions after applying the mitigation strategy. Open sky regions, represented by observation periods P1 and P4, provided the most favorable conditions. On average, GNSS receivers tracked a high number of satellites (around 37). This abundance of satellites translated into a good satellite geometry, reflected in low PDOP (Position Dilution of Precision) values (around 1). PDOP is a metric that indicates the geometric distribution of visible satellites and its impact on positioning accuracy. Lower PDOP values signify a more favorable satellite constellation, and consequently, higher positioning accuracy. In these clear sky scenarios, the resulting position errors were minimal, averaging around 1.3 m. The sub-urban environment (P2) presented a more challenging scenario. While a decent number of satellites remained visible (averaging around 27), the presence of buildings and other structures caused disruptions to the GNSS signals. These disruptions, known as multipath (MP) and non-line-of-sight (NLOS) reception, occur when the GNSS signal bounces off obstacles before reaching the receiver, leading to inaccurate positioning data. As a consequence, PDOP values rose in the sub-urban environment (up to 2.21), indicating a less favorable satellite geometry. This degraded geometry, combined with the MP and NLOS effects, resulted in a noticeable increase in position errors, with an average of 4.14 m. Urban areas (P3) posed the most significant challenges for GNSS reception. The complex building structures significantly limited the number of visible satellites, with an average of only 27 satellites tracked throughout the observation window (P3, 37 to 62 min).