# Integration of Autonomous Wireless Sensor Networks in Academic School Gardens
## 3 Results
This could be a key aspect in a star topology WSN since it is mandatory to have direct communication between the gateway and each of the wireless sensors of the network. In this way, further simulations have been performed in order to compare the performance between EnOcean STM 330 modules and a common ZigBee module operating at 2.4 GHz. The used simulation parameters are summarized in Table 1. The obtain simulation results for a wireless sensor placed in the centre of the orchard are shown in Figure 7. The RF power distribution planes at the height of the three floors of the school building are presented. As expected, 868.3 MHz shows better performance in terms of RF power level, both outside and inside the school building. Figure 6: _Cont._  
This kind of results give a valuable information for a correct deployment of the proposed WSN, as the central node of the network will be deployed within the building. Since the sensitivity of the EnOcean USB 300 central node is \(-96\) dBm, sensitivity fulfilment planes can be obtained based on the RF power distribution planes. In this case, at 868.3 MHz, the sensitivity threshold is never exceeded inside the building. This means that there are not restricted areas where the central node can be placed inside the building. But there is another important issue that has not been taken into account yet: the presence of human beings. It is well known that the presence of human body affects significantly the radio propagation due to its absorption properties, which creates the also well-known shadowing effect [42]. Depending on how many human beings are within a scenario (i.e., human body density), propagation losses vary greatly in indoor environments [43]. Based on this loss variability, in Figure 8 sensitivity fulfilment planes for approximated losses for different human body densities are presented. Three human body densities have been defined: LD (Low Density), MD (Medium Density) and HD (High Density), with their corresponding propagation losses: 10 dB, 20 dB and 30 dB respectively. The areas/zones that do not comply with the sensitivity requirements are highlighted in red, whereas the blue zone indicates that the EnOcean gateway could be deployed as the received power level \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **868.3 MHz** & **2.4 GHz** \\ \hline Output power level & 8 dBm & 8 dBm \\ Antenna type & Whip antenna & Whip Monopole \\ Antenna Gain (average) & 0.2 dB & 0.2 dB \\ Permitted reflections & 6 & 6 \\ Cuboid resolution & 2 m \(\times\) 2 m \(\times\) 2 m \\ Launched Rays resolution & 1\({}^{\circ}\) & 1\({}^{\circ}\) \\ Data rate & 125 kbps & 250 kbps \\ \hline \hline \end{tabular}
\end{table} 
Table 1: 3D Ray Launching simulation parameters. Figure 6: Linear path RF power distribution, corresponding to the white dashed line of Figure 5. (**a**) First floor height; (**b**) Second floor height; (**c**) Third floor height. is higher than the sensitivity threshold. Obtaining the sensitivity fulfilment planes for each of the deployed wireless sensors on the orchard, an optimum location for the gateway can be estimated. If the location of the gateway is restricted to specific classes or laboratories (which is usually the case), it can be assessed whether they are adequate places for the deployment or not. In this work, after obtaining all the sensitivity fulfilment planes, a laboratory and a teachers' room in the second floor have been selected as the best choices to deploy the gateway of the WSN. It is worth noting that the first-floor areas beside the orchard were also a good option but they were discarded since they were common classrooms and were defined as inappropriate. For an in-depth performance analysis, BER (Bit Error Rate) values can be calculated for both EnOcean and ZigBee options. Figure 9 shows the obtained BER for the linear path depicted in Figure 5. For the estimations, a noise level of \(-70\) dBm has been considered for both communication schemes.