## 3 Experimental Set-up
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Experiment** & \(ND_{R}\) & \(\xi_{ND}\) & \(k_{CR}\) & \(E_{CR}\) & \(P_{TX}\) \\ \hline e01 & — & — & — & — & \(-3\) dBm \\ e02 & — & — & — & — & \(-15\) dBm \\ e03 & 2 & 0 & 1 & 150 & — \\ e04 & 2 & 0 & 3 & 150 & — \\ e05 & 2 & 1 & 3 & 150 & — \\ e06 & 3 & 1 & 3 & 150 & — \\ e07 & 3 & 0 & 3 & 150 & — \\ e08 & 3 & 0 & 1 & 150 & — \\ e09 & 3 & 1 & 1 & 150 & — \\ e10 & 2 & 1 & 1 & 150 & — \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameter values used in the experiments. Figure 5: Experiment deployment; (**a**) One of the sensor nodes used in the experiments; (**b**) Deployment area. All the SunSPOTs are equipped with a CC2420 transceiver that provides radio capabilities using the 2.4 GHz for the IEEE 802.15.4. This transceiver allows a transmission power range from \(-3\) dBm to \(-32\) dBm when using channel 26, and from 0 dBm to \(-32\) dBm for the rest. The range is discrete, and the available transmission powers are shown in Table 2. For the experiments we have used channel 26, so in our case the maximum transmission power is limited to \(-3\) dBm. The nodes were deployed in an outdoor area at the facilities of the Centro de Automatica y Robotica in Arganda del Rey, as shown in Figure 5a,b. The distribution and heights of the nodes were mostly random, trying to force the use of the multi-hop routing capabilities provided by the SunSPOTs, so we could expect the creation of groups of nodes. A scheme of the deployment is shown in Figure 6. The heights were above one meter in all the nodes but in one, which was closer to the ground, at a height of about 40 cm. The base station was fixed to the outside of the stall, at an approximate height of 1.5 m.  
Figure 6 also shows the orientation of the sensors, and therefore of their inverted-F antennas. As explained in [5], the orientation of the antennas, along with the irregularity in their radiation patterns introduce a non-negligible phenomenon that has an impact in the strength of the received signal (RSSI). The orientations were also selected randomly. In the previous section we have introduced the idea that the control system is executed periodically. The interval used in the experiments was fixed to 20 s in order to guarantee the neighbor discovery and the route establishment for all the status messages generated in each iteration. A shorter interval may be used taking into account the number of messages that can be generated in each iteration and the values obtained in [19]. Moreover, each sensor node was configured to sent a status message addressed to the base station at the end of each iteration of the control system. \begin{table}
\begin{tabular}{c c} \hline \hline
**Channel** & **Available Transmission Powers (dBm)** \\ \hline
11 to 25 & \(-32\), \(-31\), \(-30\), \(-25\), \(-22\), \(-19\), \(-17\), \(-15\), \(-13\), \(-12\), \(-11\), \(-10\), \(-9\), \(-8\), \(-7\), \(-6\), \(-5\), \(-4\), \(-3\), \(-2\), \(-1\), 0 \\ \hline
26 (default channel) & \(-32\), \(-31\), \(-30\), \(-25\), \(-22\), \(-19\), \(-17\), \(-15\), \(-13\), \(-12\), \(-11\), \(-10\), \(-9\), \(-8\), \(-7\), \(-6\), \(-5\), \(-4\), \(-3\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Available transmission powers in the SunSPOT nodes. Figure 6: Experiment deployment.