# EMF Assessment Utilizing Low-Cost Mobile Applications
## 3 Results
### Received Power Variability  
The variability of the total received power was evaluated using the coefficient of variation (CV) due to significant differences in received power values between segments. For each of the five received power calculations, the standard deviation and mean of the received power table (5 \(\times\) 17 \(\times\) 167) were calculated across all route repetitions for each segment. The CV was then obtained by dividing the standard deviation by the mean value [22].  
To understand why some areas exhibited higher variability than others, Figure 6 visualizes the segments with the top 15 highest CV values for each received power calculation for the first route.  
Although there were some scattered points with high CV along the route, four distinct areas with high CV values were observed for both the exposimeter and the app received power (a-d). To identify common factors in these areas, we first examined the traffic conditions. According to the \"TrafficThess\" website [23], all four locations are known to experience traffic jams or are in close proximity to traffic jams during rush hours (Figure 7).  
These areas are shown in Figure 8 with images obtained from Google Street View. In these images, taken randomly and not during rush hours, we observed high traffic congestion.  
Although high traffic loads are common in high CV areas, other areas, such as the street between locations (a) and (b), also experienced high traffic during rush hours despite having lower CV values. This suggests that there must be other key factors as well that contribute to the high variability of received power. One such key factor is the height of the installed antennas. This is because when the line of sight (LOS) is interrupted only on high-traffic days, high CV values are expected.  
Figure 6: Segments with top 15 CV values of each received power calculation. Areas (a–d) are characterized by high CV values for both the exposimeter and app received power.  
This indicates that in high-traffic areas with Small Cell Antennas (SCA) installed at low heights (usually 3-10 m), rather than macro cell antennas placed on rooftops (above 10 m), a high CV value is expected due to changing LOS conditions. Observing the area of high traffic load between (a) and (b) in Figure 9, we noted that the mobile antennas are placed on the rooftop of a tall building, reducing the likelihood of LOS interruption and thus resulting in lower CV values.  
Figure 10 illustrates the BSs in Thessaloniki, categorized by height, with areas of high CV values also marked. It is evident that in areas (b), (c), and (d), there is a high concentration of SCAs, leading to changes in the LOS situation during high traffic loads.  
Conversely, in area (a), only macro cell antennas are present, positioned at greater heights. The high CV values in this area resulted from interruptions in LOS during heavy traffic conditions between the measurement point and the BSs located between areas  
Figure 8: High received power CV areas: (**a**) Area Stathmou; (**b**) area Nikis; (**c**) area Egnatia; (**d**) area Mitropoleos [24].  
Figure 7: Thessaloniki TrafficThess map for a selected date and hour known for high traffic [23]. Areas (a–d) are characterized by high CV values for both the exposimeter and app received power.  
It is worth noting that more segments had high CV values within the first route; only some with the highest values are highlighted here. These findings also applied to the second route, indicating that areas with frequent traffic jams and small cell antennas installed at low heights exhibit significant variability in received power values.