# Integration of Autonomous Wireless Sensor Networks in Academic School Gardens
## 3 Results  
As previously mentioned, a radio planning study has been performed in order to obtain information about the feasibility of the proposed EnOcean-based WSN for the monitoring of the school orchard. The scenario under analysis has been presented in Figure 1 and the created scenario for the simulations by means of the 3D Ray Launching tool is presented in Figure 4a. The simulated scenario is composed by the 'Camino de Santiago' public school building and the orchard which is part of its facilities. They are distributed in a 2470 m\({}^{2}\) area scenario, where the orchard occupies 237.5 m\({}^{2}\). The building has dimensions of 40 m long, 28 m width and 9 m height. It is worth noting that important elements in terms of its effect on radio propagation have been taken into account such as the interior of the school building, which has been filled approximately like the real building (see Figure 4b) and the metallic fence that surrounds the orchard (see Figure 4c). The material properties (dielectric constant and conductivity) of all the elements within the scenario, including organic materials for trees and orchard have also been considered. Figure 3: Schematic description of the star topology of the network with the EnOcean’s USB 300 Gateway central module. The main results provided by the 3D Ray Launching simulation tool are the RF power distribution planes. A transmitter is located within the created scenario and parameters such as transmission power level and antenna type are defined. Then, results for the whole volume of the scenario are obtained for each of the deployed wireless transmitters. As an illustrative example, Figure 5 shows the estimated values for a bi-dimensional plane at 5 m height for the simulation of one of the wireless sensors deployed on the orchard (represented by a red dot). The typical RF power distribution due to the presence of a bi-dimensional plane is shown in Figure 5.  
Figure 4: (a) Created scenario for the 3D Ray Launching simulations; (b) Detail of the building; (c) Detail of the metallic fence of the orchard. multipath propagation can be seen in the figure, which is caused by the morphology and topology of the considered scenario. Instead of the required process for 3D Ray Launching simulations, a faster methodology to obtain the received RF power at one point of the scenario has been also used, by means of empirical radio propagation models such as COST-231. These methods are based on measurement campaigns and provide very fast estimations. However, they lack precision since they do not take into account the multipath propagation which is specific for each scenario due to the elements within them such as furniture, columns, fences and so forth. In order to see clearer the difference between empirical methods and the 3D Ray Launching method, three linear path RF power distributions are shown in Figure 6. They correspond to the linear path marked by a white dashed line in Figure 5 and the presented heights (1.2 m, 4.25 m and 7.25 m) are equivalent to the tables' heights of the first, second and third floor of the building, that is, the potential locations of the EnOcean gateway. As can be seen in all the graphs of Figure 6, the estimations provided by the 3D Ray Launching follow the tendencies of the other radio propagation models but they reflect the typical rapid variations generated by the multipath propagation, giving more precise results for an optimized radio planning. One of the issues which were taken into account when wireless sensors were chosen, apart from the self-powered feature, was the operation frequency of the transceivers. As presented in the Introduction section, in the literature almost all WSNs deployed for Smart Agriculture use ISM 2.4 GHz band for the wireless communication. The EnOcean STM 330 devices (EnOcean GmbH, Oberhaching, Germany) used in this work operates at 868.3 MHz, which means that in same conditions (same transmitted power level and antenna), the coverage or reach of these nodes is higher than those operating at higher frequencies.