## 4 Materials and Methods
### Experimental Setup  
The experiments were performed in an open area at the facilities of the Centro de Automatica y Robotica of the Consejo Superior de Investigaciones Cientificas in Arganda del Rey (Spain). The base station was fixed to the outside of a stall at an approximate height of 1.5 m. The deployment of the nodes can be decided either by deterministic or random mechanisms [28; 29]. The connectivity is related to the sensing coverage [30], and in a deterministic deployment, the transmission power for each node can be estimated beforehand to get a k-connected network. Therefore, we have chosen a random deployment where our proposed self-adaptive system can be used to dynamically adjust the transmission power. This adjustment is used to reach a steady state where the connectivity can guarantee a good packet delivery rate while keeping the energy consumption as low as possible. The only restriction we have considered for the locations is that the farthest node from the base station should be at a distance that maximizes the chances of using the multi-hop capabilities of the underlying routing protocol.  
A scheme of the deployment is shown in Figure 9. The schema includes information about the identities of each node and the distances between them. The heights for the sensor nodes were above one meter in all cases, but one, which was closer to the ground at a height of about 40 cm.  
Figure 9 also shows the orientation of the antennas, as this factor along with the irregularity in their radiation patterns introduces a non-negligible phenomenon that has an impact in the strength of the received signal (RSSI) [31]. The orientations were also random.  
The scenario was in an isolated area, so no radio interferences were expected. The radio channel used was the default Channel 26. The transmission power for this channel is restricted to the range from \(-3\) dBM to \(-32\) dBM [32]. All of the sensor nodes start each experiment at the lowest available transmission power. At each iteration of the control loop, the self-adaptive system readjusts the transmission power according to the number of neighbors. The interval of the monitoring loop was set to 20 s.  
The parameters being evaluated were:  
* \(ND_{R}\) with the possible values of two and three.
* \(\xi_{ND}\) with the possible values of zero and one.
* \(k_{CR}\) with the possible values of one and three.  
Figure 9: Deployment, distances and nodes orientation.  
The \(E_{CR}\) parameter was fixed to a value of 150 mAh.  
As this was a reduced set of values, it was considered worthy to perform a factorial design of the experiments. Additionally, two control experiments were included using a fixed transmission power with no self-adaptive system running, but in equivalent conditions. That is, the rest of the activities performed by the nodes, like the discovery of their neighbors and the collection and report of sensed data, remained the same. The two control experiments provided a set of reference values to compare with those obtained from the use of the self-adaptive system. Table 2 summarizes the values used in each experiment, where e01 and e02 refer to the two control experiments already mentioned. It also collects the results obtained in [10] related to the energy consumption and the connectivity.