# Communication Interface Manager for Improving Performance of Heterogeneous UAV Networks
## 6 Obtained Results
### MAC and PHY Evaluation
This was also observed when interfaces were applied homogeneously. These intervals included the time of establishment and spread of the signal by the nodes in the spectrum (the nodes become audible). Thus, from a 20 to 50 m distance between the nodes, we verified that the IM presented a performance similar to IEEE 802.11n, maintaining the signal reception to between \(-60\) and \(-75\) dBm,  
Figure 11: Rx power per distance (m) using aggregate samples intervals of 100 ms.  
which is considered a good reception quality for the 802.11 standard. However, the 802.11p interface showed better performance, maintaining the signal reception around \(-65\) dbm, which is considered an excellent reception quality, maintaining the link at these levels up to a 70 m distance between the nodes. The IM possibly chose 802.11n more often due to the higher volume of transmitted bytes (Figure 10), lower attenuation received (Figure 12), and lower delay generated (further discussed). For the five- and eight-node scenarios, the IM performance was similar to that of 802.11p. As shown in Figure 10b,c, the IM decision was predominantly for 802.11p. An important observation here is that the large number of samples obtained caused a denser curve compared with the 802.11p experiment. This means that the IM switching caused a better signal reception on the network in general, allowing maintenance of message exchanges with good reception power with larger distances between nodes: 70 m (five nodes) and 120 m (eight nodes). The performance of the Rx power presented by the network operating with IM is considered very good, since it maintained the levels of signal reception at levels classified as high reception for networks constituted by the 802.11 protocol; this allowed network traffic over greater distances between nodes and maintained the connection for a longer period of time, as shown in Figures 10 and 12. In SAR missions, the connection time intervals and greater signal reception by the nodes during the flight are desirable features in the constitution of mobile networks composed of such high-mobility nodes. Figure 12 shows the loss in dB from the network during the UAV trajectories. These experiments correspond to the average value obtained in each aggregated sample, considering the attenuation caused by Nakagami fading and the power received by neighboring nodes. Figure 12: Loss (dB) versus distance (m) using aggregated samples of 10 ms. The loss (dB) for interface manager experiments in the five- and eight-nodes scenarios presented the lowest signal loss indexes, maintaining a rising curve up to about 82-85 dB. This means that \(~{}30\%\) of the path signal attenuation was caused by multi-path transmissions and fading effects between Tx and Rx nodes. In Figure 12, for the three-node experiment, the loss obtained by the IM experiments is similar to that of 802.11n, once the IM decided to use this interface more. However, during 0-30 m, the IM alternated, presenting minor losses compared with 802.11n maintaining the losses between 85-100 dB. Additionally, the variable values of loss from 30 m demonstrated that the IM attempted to decrease this rate, impacting the overall network performance. The thicker curves generated by the five-node and eight-node scenarios represent a larger volume of data trafficked by the nodes, which can be constituted by messages and by beacon frames along their trajectories. An important point is that the UAVs remained able to communicate for a longer time, reaching greater distances. This is more evident using as reference the typical loss of 802.11n systems of 80 dB in the 2.4 GHz band and 86 dB in the 5 GHz band considering a 100 m distance between the source transceiver and the destination transceiver obtained by free space loss attenuation, which implies a \(-60\) dBm reference Rx power [45]. So, the IM and 802.11p performance for the five-node and eight-node scenarios presented a 85 dB loss maximum with an Rx power of \(-50\) to \(-70\) dBm (Figure 11).