# Communication Interface Manager for Improving Performance of Heterogeneous UAV Networks
## 6 Obtained Results
### MAC and PHY Evaluation  
This section highlights the effects of the proposed IM on standard wireless network metrics. The first metric to be discussed is the amount of application-related data (payload) received by each node, as depicted in Figure 10.  
The amount of data generated in the three-node scenario was 5096 Mb, 4011 Mb for the five-node scenario, and 4233 Mb for the eight-node scenario. Figure 10 shows the amount of bytes received by the network in 5 s intervals. The IM decisions (interfaces switching) are also presented. These decisions are composed of the aggregated average of decisions of 5 s, presented using labels with the IM curve. The labels represent the aggregate decision composed of blocks of sample intervals, which the IM considered in most decisions. This means that the interface shown in the samples is the one chosen by the IM on most of the nodes in a given time interval. With respect to the payload transmission in bytes received (Mb), the IM performed the best only in the three-node scenario (Figure 10a). The IM initially chooses the IEEE 802.11n interface, changing to the IEEE 802.11p interface in the intervals of 20, 40, 48, and 65 s to maintain the growing curve of the transmitted bytes. Thus, for the scenario with three nodes, 802.11n provided a higher transmission rate until to the end of the experiment (141 s). When using homogeneous interfaces, data transmission was interrupted before reaching the end of the experiment, reducing the amount of data received. For the five- and eight-node experiments, the IM predominantly selected 802.11p, only using 802.11n in the initial 15 s. Three factors can explain the reasons for this occurrence: nodes reached longer distances from each other during the route, up to 75 m in the three-node and up to 100 m in the five- and eight-nodes experiments; the sparser layout of routes; and, lastly, the Rx power factor in the decision tree reasoning. As shown in Figure 11, most of the time 802.11p presented an Rx power between \(-50\) and \(-65\) dbm, which indicates a \"Good\" or \"Strong\" signal. The volume of bytes transmitted was smaller than in the experiment with three nodes, as 802.11p has a smaller bandwidth compared with 802.11n. Less traffic was generated (CBR data rate). However, this interface achieved lower flow rates,  
Figure 10: Bytes received (Mb) by the PHY layer by aggregated time intervals (s). so we were able to notice a stability in the transmission, which represented a continuous growth with less fluctuations, maintaining the connection without interruptions. Another observation was that in the five- and eight-node scenarios, the UAVs trajectories covered wider areas, allowing UAVs to be more distant from each other at certain points. Theoretically, the IEEE 802.11p on its on-board unit (OBU) version can reach a coverage of up to 1 km, which would justify its preference given its longer communication range. Although, the IM did not present the best performance in terms of received bytes in the PHY layer in the five- and eight-node experiments, we observed that achieved values for the IM are satisfactory because the IM presented the best performance in terms of effective message delivery at the application level, as shown in Table 3 and Figures 8 and 9. An effective message delivery means that more messages were successfully delivery at the destination, probably because of the linear and continuous behavior of the PHY layer, with suitable Rx power and loss, which allowed a better message recovery performance at the destination. Figure 11 presents the performance of the average aggregated of Rx power obtained by nodes over the sample time intervals. For experiment, a sharp curve can be observed, equivalent to the samples derived from the average signal power received from the nodes during their trajectories. For the three-node experiments (Figure 11), where the interface manager decided more often to use the 802.11n interface, we verified that up to a 10 m distance between the nodes, the reception power increased up to \(-60\) dBm.