## 4 Measurements and Testing of the Measuring System
### Network Load Testing  
#### 4.3.1 Measurements of Radio Band Occupancy  
The network load status test was carried out both in terms of radio band occupancy and data transmission. During the performed tests, the WSS transmitted data in accordance with the previously developed measurement protocol. Measurements of radio band occupancy depending on the frame transmission frequency \(\mathrm{f_{T}}\) and the length of transmission frames were carried out using the measuring station presented in Figure 1. The spectrum analyser (SA) performed the measurements in the RTSA (Real-Time Spectrum Analyser) mode and displayed spectrograms. The measurements were performed in the frequency range from 2.39 GHz to 2.43 GHz. The WSS sensor module communicated with the RT access point using channel 1 (2.412 GHz). The acquisition time of one measurement was set to 24.996 ms. The measurement antenna directed at the WSS was 1 m away. The band occupancy tests, depending on the test case, were performed on the basis of the analysis of recorded spectrograms, where the X axis represents the frequency, and the Y axis represents the time. The Y axis consists of 483 points, with each point representing a single SA analyser measurement (24.996 ms). The signal strength measurement range represented by the spectrogram colours is from \(-\)100 dBm to 0 dBm. However, it was limited and ranged from \(-\)72 dBm to \(-\)27 dBm (Ref Hue Pos was set to 73 and Bottom Hue Pos to 28). Measurements were taken for all the test cases from P1 to P26 and, additionally, a measurement was performed with the sensor module turned off to determine the effect of ambient noise on the other measurements. The measurement results were saved as bitmaps presenting spectrograms. For the purposes of further analysis, the spectrogram colours were changed. The default colour range (Figure 9a) was converted to grayscale from the hexadecimal value range 0 xFFFFF (white) to 0x242424 (dark grey), where white is the highest measured signal strength (Figure 9b). From each image, the central part of the monitored band with a range of about 18 MHz was selected. Then, each image was thresholded with the values of 75, 100, 125, and 150 (from the range of 0-255, where 0 is black, 255 is white). \begin{table}
\begin{tabular}{c c} \hline \hline
**Cases** & **RMS Current (mA)** \\  & **Mean \(\pm\) Std** \\ \hline P1 & 200.97 \\ P2, P8, P14, P19, P24 & 241.99 \(\pm\) 0.48 \\ P3, P4, P5, P6, P7, P9, P10, P11, P12, P13, P15, & \\ P16, P17, P18, P20, P21, P22, P23, P25, P26 & 250.82 \(\pm\) 0.55 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: WSS current consumption depending on the defined measurement case. For each of the processed images (Figure 9c), the percentage of white was calculated, which represents the band occupancy. Regardless of the adopted threshold value, the share of white in the background image does not exceed 2.2%, so it can be concluded that the background noise did not have a significant impact on the measurement results. Figure 10 shows a graph of the percentage of white in the images as a function of the frequency \(f_{T}\), for various threshold values (thd). For individual threshold values (75, 100, 125, and 150) and measurement cases with the same maximum frame transmission frequency \(f_{T}\), the obtained values of the percentage of white are similar, because the difference between the mean and the individual percentage values does not exceed 3.7%. For this reason, cases with the same maximum frame rate were analysed as being equivalent. Moreover, irrespective of the threshold value, the curves of the percentage of white for the measurement cases with the maximum frequency \(f_{T}\) are of a similar nature (Figure 10). Table 4 shows the mean percentage reduction in the band occupancy for transmitting frames at 5 Hz, 15 Hz, and 30 Hz, relative to transmission at 60 Hz, calculated using all curves. Figure 10: Graph of the proportion of white in the images depending on the frequency \(f_{T}\).