## 4 Discussion
### Repeated Measurements in the Same Areas  
To confirm the extent to which the measurement results vary depending on the driving time and other factors, we repeated measurements in the range of 1 km\({}^{2}\) at two urban areas (Urban A and B) and two suburban areas around Tokyo (Suburban A and B) and one metropolitan area between May 2021 and February 2022 using the conditions shown in Table 5. For Urban area A, Suburban area A, and the metropolitan area, measurements were performed five times during the day and night on both weekdays and holidays and repeated four times during the period shown in Table 5 (80 times/area). Note that the number of valid measurement data is 78 for Urban A. For Urban area B and Suburban area B, measurements were repeated only during the day (40 times/area). \begin{table}
\begin{tabular}{c c} \hline \hline
**Route** & **Averaged Difference [dB]** \\ \hline Route 1 & 0.6 \\ Route 2 & \(-\)0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Averaged differences between normal three-axis and separate measurements. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{3}{c}{**Combination**} \\ \cline{2-5}
**Area** & **Day** & **Daytime/ Nighttime** & **Number of Repetitions per One Condition** & **Number of Combinations** & **Total Number of Valid Measurements** \\ \hline Urban A & & & & 78 \\ Suburban A & & Day/Night & & 80 \\ Metropolitan & & Holidays & & 5 & 4 & 80 \\ Urban B & & Day & & 40 \\ Suburban B & & & & 40 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Conditions of repeated measurements during May 2021 to February 2022. Table 6 shows the average driving speed. It is clear that the average driving speeds were less than about 25 km/h, similar to that in the wide-area measurement. The maximum, minimum, 90 th, 50 th, and 10 th percentile values were calculated for each area under all the conditions shown in Table 5. Although the number of data obtained by one driving measurement varied by area and time of day, it was approximately 200 to 400. The standard deviation of the median (50 th percentile) value in each area is shown in Table 7. Note that there was no marked difference by period, day of the week, and time zone, and the standard deviations were 3 dB or less, as shown in Table 7.  
Figure 6 shows the box plot of the integrated E-field strength distribution for the mobile systems. The measurement results using the car show the average results of the maximum, minimum, 90 th, 50 th, and 10 th percentile values over all measurements per area shown in Table 5. For comparison, the results of the past spot measurement [1] are also shown. Note that no spot measurement in the metropolitan area had been performed in the past. The spot measurements were carried out at the point of 10 \(\times\) 10 (100 m\({}^{2}\) per one point) in the area of 1 km\({}^{2}\), but the data at the points where a car cannot be driven were removed and recalculated with the remaining measurement points. The E-field strength in the spot measurement was averaged over 1 min. The results of the car measurement show that the E-field strength is higher in the order of metropolitan areas, urban areas, and suburban areas. This tendency is also consistent with the results of spot measurement [1]. In addition, when the results of spot and car measurements were compared at the median value for the same area, it was found that the electric field strengths were almost at the same level within 4 dB. \begin{table}
\begin{tabular}{c c} \hline
**Area** & **Average Driving Speed [km/h]** \\ \hline Urban A & 16.8 \\ Suburban A & 25.4 \\ Metropolitan & 13.6 \\ Urban B & 16.2 \\ Suburban B & 21.9 \\ \hline \end{tabular}
\end{table} 
Table 6: Average speed in repeated measurement. \begin{table}
\begin{tabular}{c c c c c c} \hline
**System** & **Urban A** & **Urban B** & **Suburban A** & **Suburban B** & **Metropolitan** \\ \hline FM & 0.73 & 0.76 & 1.6 & 1.6 & 0.5 \\ TV & 1.7 & 0.88 & 2.3 & 3.0 & 0.6 \\ Mobile & 1.6 & 1.1 & 2.3 & 0.74 & 1.3 \\ \hline \end{tabular}
\end{table}