## 7 Results
### Channel-Specific Accuracy  
In this section, the in-channel classification accuracy will be analyzed for all of the locations included in the tests. In Figure 7, we show the detection accuracy for Location A for a sampling window of 150 ms, together with information collected by means of the spectrum analyzer, showing the energy density in the 2.4-GHz ISM band at the industrial site. We chose to show the results for a shorter sampling window (150 ms) with respect to the previous section in order to highlight the impact of this aspect on the classification accuracy. As can be seen, even with this short sampling window, the detection rate ranged around 90% for the channels overlapped by the \(\{1,\ 6,\ 11\}\) configuration of the IEEE 802.11 network, while the IEEE 802.15.4 Channels \(\{15,\ 20,\ 25,\ 26\}\) were accurately reported free from interference. In Figure 8, we show the classification outcome for Location B. In this test scenario, there are multiple IEEE 802.11 networks occupying IEEE 802.11 Channels 1, 6 and 11, while a distant access point with an average RSSI level \(<-80\) dBm at the data collection point was present on Channel 7. As expected, while IEEE 802.15.4 Channels \(\{15,\ 25,\ 26\}\) were reported free in more then 85% of the tests, the decision for Channels 19 and 20 was uncertain since the IEEE 802.11 network was reported in only around 40-50% of the tests. We select this scenario to stress the performance of the proposed solution in the presence of an access point, which is barely detectable at the channel sensing location. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Channel Status** & \multicolumn{4}{c}{**Detected Interference Source**} \\ \hline  & **IFC** & **IEEE 802.11** & **Microwave Oven** & **Unknown** \\ \hline
**IFC** & 84.9\% & 11.2\% & 3.8\% & 0.1\% \\
**IEEE 802.11** & 10.7\% & 77.9\% & 5.2\% & 6.1\% \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Average classification accuracy for the 250 ms sampling window for Location B. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Channel Status** & \multicolumn{4}{c}{**Detected Interference Source**} \\ \hline  & **IFC** & **IEEE 802.11** & **Microwave Oven** & **Unknown** \\ \hline
**IFC** & 98.2\% & 1.7\% & 0.1\% & 0.0\% \\
**IEEE 802.11** & 0.1\% & 98.9\% & 0.3\% & 0.7\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Average classification accuracy for the 250 ms sampling window for Location A. In Figure 9, we show both the classification rate at Location C for a MWO and the average RSSI value and the standard deviation for the collected test data. As mentioned beforehand, while the RF leakage from MWO spans all along the 2.4-GHz ISM band, the detection accuracy presents considerable variations along the 16 IEEE 802.15.4 channels. In particular, the eight channels 16-23 seem to offer the best chance for microwave detection, while Channel 21 shows the maximum classification accuracy. This is because, as reported in [36] and the references therein, the residential MWOs have an emission peak frequency around 2.45 GHz, which corresponds to Channel 20 in the IEEE 802.15.4 mapping. In this case, we are likely to be experiencing an MWO with center emission frequency at 2.455 GHz, which consequently triggers a very high detection rate on Channel 21. Nevertheless, since the emission pattern may vary from model to model, the channel-specific performance is expected to vary from the one shown in Figure 9. In any case, for any model, the average detection accuracy is expected to remain consistent, since there will always be a region of maximum emission inside the ISM band of interest. Figure 7: Location A, three IEEE 802.11 access point operating on IEEE 802.11 Channels \(\{1,\ 6,\ 11\}\). (**a**) Channel-specific detection rate at Location A for the sampling window length of 150 ms; (**b**) IEEE 802.11 power spectral density (PSD) as observed by the channel analyzer.