## 7 Evaluation  
The evaluation of the presented method is performed beginning with a simulated interfering environment. It has been done so to have an illustrative interfering noise, coming from both static and dynamic (frequency changing) networks, and with significant RSSI values. Even though the same analysis could have been done starting from real RSSI measurements of any specific scenario. To help in the evaluation of the method, a simulation tool has been developed using Matlab. The developed tool allows to define the interfering environment, deploy the network under study and graphically visualize the results of the calculations. Figure 16 shows the main window of the developed simulation tool. The interfering environment is simulated by placing potential coexisting networks close to the network of interest. The simulation tool allows to choose between different standards: IEEE 802.11, IEEE 802.15.1 and IEEE 802.15.4. As an illustrative example, let us consider the deployment of an IEEE 802.15.4 network as represented in Figure 17, consisting of four sensor nodes (black dots) that have to communicate with a gateway (G). The network has to coexist with one IEEE 802.11 (WLAN), two IEEE 802.15.4 (LR-WPAN A and LR-WPAN B) and one IEEE 802.15.1 (Bluetooth) networks (coloured markers) located close to the gateway. Our IEEE 802.15.4 network has the ability to hop among the available 16 channels. Figure 16: Main interface of the simulation tool. The left panels contain buttons to configure the analysis parameters and select the different plotting options. The right panel is reserved for the graphical representation of the results. The different type of results are represented in their corresponding tab within the graph panel. From the transmission power of each interfering network, the interference noise is calculated at every location of the nodes of the network under study. The signal propagation is modelled according to the free-space path loss (Equation (26)). The transmission powers of the interfering networks are shown in Table 2, along with the transmission power and the receiving sensitivity of the network of interest. The developed tool allows to configure the observation and operation times, as well as the hopping time and the slot times of each network. For the reduced hop set techniques, the number of channels to employ must be defined as well. Table 3 summarizes the time parameters employed in the evaluation example. The interference noise is observed for 0.1 s and, then, the connections of the network of interest are evaluated for an operation time of 0.9 s. Therefore, the total analysis time results in 1 s, with a time resolution (time step) of 1 ms. The slot and wait times of all the networks are set to the same values: 3 ms and 2 ms respectively. For the WSN of interest and the interfering Bluetooth network, the hop times are set to 5 ms, meaning that every 5 ms these networks hop from one frequency channel to another. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{4}{c}{**INTERFERENCE**} & **WSN** \\ \cline{2-5}  & **WLAN** & **Bluetooth** & **LR-WPAN A** & **LR-WPAN B** & **802.15.4** \\ \hline TRANSMISSION POWER & 100 mW & 2.5 mW & 1 mW & 1 mW & 1 mW \\ RECEIVING SENSITIVITY & - & - & - & - & \(-90\) dBm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Transmission powers and receiving sensitivities for the interfering networks and the wireless sensor network under study. Figure 17: Example of an 802.15.4 network deployment with four nodes (black dots) and a gateway (G). The gateway is surrounded by four interfering networks (coloured markers). The IEEE 802.11 (WLAN) and the interfering IEEE 802.15.4 (LR-WPAN A and LR-WPAN B) networks transmit in static frequency channels, while the IEEE 802.15.1 (Bluetooth) network hops from frequency to frequency in a random way. For simplicity, a reduced set of seven channels have been selected from the available 79 of the Bluetooth network.