# Spectral and Energy Efficiency Trade-Off in UAV-Based Olive Irrigation Systems
## 3 Results  
In this section, we numerically evaluate the performance of our proposed UAV-based olive irrigation system. Specifically, we focus on the consumed circuit power of the studied system. We also analyze the energy efficiency and spectral efficiency trade-off. We determine the optimal network parameters in order to obtain the maximum energy efficiency. In Table 1, we give the simulation parameters. In Figure 3, we present the circuit power (CP) of the proposed UAV-based olive irrigation system with reference to the number of IoT devices \(K_{I}\). We consider two diversity \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Value** \\ \hline Number of cells (L) & 10 \\ Cell radius & 250 m \\ SNR & 0 dB \\ \(\tau_{u}\) & 90 \\ \(\tau_{d}\) & 90 \\ \(\tau_{c}\) & 200 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation parameters. combining techniques: the M-MMSE (Multicell Minimum Mean Squared Error) combiner along with the MR (Maximum Ratio) combiner. Further, two amounts of GBS antennas were selected: \(M=100\) and \(M=200\). In Figure 4, we present the circuit power (CP) of the proposed UAV-based olive irrigation system with reference to the number of GBS antennas. As in Figure 3, we consider two diversity combining techniques: the M-MMSE combiner along with the MR combiner. Additionally, two different numbers of IoT devices are examined: \(K_{I}=10\) and \(K_{I}=20\). In Figure 3 (respectively, in Figure 4), we notice that for the two considered combiners, the total circuit power increases with \(K_{I}\) (respectively, with \(M\)). The previous figures also illustrate the fact that the M-MMSE combining technique consumes a higher CP than the MR combining technique. Indeed, the M-MMSE scheme requires the inversion of an \(M\)-dimensional matrix, whereas no matrix inversions are required in the MR scheme. We analyze in Figures 5 and 6 the proposed UAV-based olive irrigation system's energy efficiency and spectral efficiency trade-off problem. We consider different numbers of GBS  
Figure 4: Circuit power (CP) of the proposed UAV-based olive irrigation system with reference to the number of GBS antennas \(M\), for a multi-cell MMSE combiner, an MR combiner, and different numbers of IoT devices \(K_{I}\). Figure 3: Circuit power (CP) of the proposed UAV-based olive irrigation system with reference to the number of IoT devices \(K_{I}\), for a multi-cell MMSE combiner, an MR combiner, and different numbers of GBS antennas, \(M\). antennas \(M\in\{20,40,100,200\}\) and \(K_{I}=20\) in Figure 5. However, we consider different numbers of IoT devices \(K_{I}\in\{5,20,50\}\) and \(M=20\) in Figure 6. From both figures, one can see that the energy and the spectral efficiency trade-off curve is an unimodal function of \(M\) (as it is for \(K_{I}\)). In Figure 7, we plot the energy efficiency of the proposed UAV-based olive irrigation system as a function of the throughput. We also consider two diversity combining techniques: the M-MMSE combiner along with the MR combiner. The results are obtained by varying the number of IoT devices \(K_{I}\) as well as the number of GBS antennas \(M\). As illustrated in Figure 7, the maximal energy efficiency value with the MR combiner (respectively, the M-MMSE combiner) is about 9 Mbit/Joule (respectively, 20 Mbit/Joule), which corresponds to a throughput of 330 Mbit/s/cell (respectively, 600 Mbit/s/cell) when \(K_{I}=10\). Consequently, the M-MMSE combining technique performs better and achieves the maximal EE. This can be explained by the fact that in massive MIMO communication, the M-MMSE scheme exploits the spatial degrees of freedom (offered by multiple antennas) to focus signals on intended receivers, reduce interference, and consequently increase the system throughput [32]. Hence, M-MMSE improves the energy efficiency, since the higher  
Figure 5: Energy efficiency versus spectral efficiency of the proposed UAV-based olive irrigation system for different numbers of GBS antennas \(M\) with the number of IoT devices as \(K_{I}=20\).