## 4 Test Environments  
The selected environments correspond to three typical Wi-Fi network deployment zones, each chosen to represent varying levels of spectrum saturation. These differences arise due to the distinct characteristics of each environment, such as the density of wireless devices, the number of overlapping networks, and the presence of external interference sources. Evaluating these diverse conditions enables a comprehensive analysis of the performance of different IEEE 802.11 technologies under real-world interference and congestion scenarios. To quantify these differences and better understand the spectrum conditions in each environment, a spectrum analysis was conducted. This analysis consists of capturing and visualising the frequency activity within the selected bandwidth over time. In these captures, the horizontal axis represents the frequency range, while the vertical axis corresponds to time. The resulting spectrograms provide a colour-coded representation of spectrum occupancy, where, in general, blue indicates an unoccupied or low-activity spectrum, while other colours signify increasing levels of signal presence and interference. However, the shades of these heats vary depending on the background noise level of the environments selected for testing. For example, the spectrogram shown in Figure 3 captures the activity of the 2.4 GHz band, displaying a 100 MHz bandwidth analysis, spanning from 2.4 to 2.5 GHz, divided into 10 MHz slots for enhanced visualisation. The temporal representation covers 6 s, with millisecond resolution, allowing observation of the spectrum's dynamics. A high concentration of activity, characterised by a transition from blue to red (low to high saturation), is evident in the first 30 MHz of the spectrum, indicating the intensive use of Wi-Fi channels 1-3 and consequent congestion. Moving toward higher frequencies, the activity decreases, showing weaker and more intermittent signals, suggesting the presence of other networks or interferences with less impact. This information is crucial for optimising the Wi-Fi network, enabling the selection of channels that are less congested and minimising interference. Consequently, spectrogram analysis was used to estimate the percentage of the spectrum occupied by interfering networks. To assess the spectrum conditions in each environment, spectrogram captures were taken using the Anritsu MS2090A spectrum analyser. Figure 4 shows each capture visualising seven seconds of the analysed spectrum, providing a snapshot of frequency activity immediately before conducting the performance tests. These spectrograms offer insight into the spectral occupancy within the three selected environments, highlighting variations in interference levels across the three usable frequency bands. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multirow{2}{*}{**Environment**} & \multicolumn{4}{c}{**Communication Distance**} & \multirow{2}{*}{**Line of Sight (LoS)**} & \multirow{2}{*}{**Indoor/Outdoor**} \\ \cline{2-2} \cline{6-7}  & **5 m** & & & & **15 m** & 45 m & 60 m \\ \hline Laboratory Area & ✓ & ✓ & ✓ & ✓ & ✓ & Indoor \\ Residential Area & ✓ & ✓ & & ✓ & ✓ & Outdoor \\ Factory & & ✓ & ✓ & & & Indoor \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Configurations parameters used during the second round of experimental evaluation. Figure 4: Level of spectrum occupancy observed in residential, laboratory, and industrial environments at 2.4 GHz, 5 GHz, and 6 GHz bands. Figure 3: Spectral analysis of the 2.4 GHz band over a 100 MHz span, showing signal activity and interference levels. In the residential environment, the spectrograms reveal minimal spectral activity across all three frequency bands. In the 2.4 GHz band, the spectrum is mostly blue, indicating low levels of interference and occasional transmissions. The 5 GHz band also shows predominantly blue areas, reflecting sparse utilisation, which is typical in residential areas where fewer devices operate on this band.