## 5 Results
This is almost two times the amount of packet life time observed in Scenario 2 and thus does not adversely impact the quality of the voice communication. The average packet lifetime for the AODV protocol is not shown in the figure. The reason for this is that the average packet lifetime of AODV is more than 100 times longer than that of HDARP for Scenario 1 and more than 5 times longer than that of HDARP for Scenario 2. One drawback of using directional antennas is that a receiver may suffer from destructive interference from two or more simultaneous senders without the senders being aware  
Figure 6: Average number of leaked packets when using directional antennas (99% confidence interval), for Scenario 1 (**upper**) and Scenario 2 (**lower**). of the problem (c.f., discussion about unit disk radio in Section 4). An example would be if A and B simultaneously sent to C in Figure 3 on the same frequency. Therefore, one could expect that the HDARP protocol could suffer from a low packet delivery ratio. Figure 8 shows that the packet delivery ratio of the HDARP protocol is on a par with the best of the other protocols for Scenario 1 but a bit lower for Scenario 2. This means that the extra packet loss due to avoiding leakage seems limited. In some situations, HDARP will not be able to find a route that is free from leakage risks. However, in such cases, the packet will still be delivered (see how _weight_ is handled in Algorithm 4). This means that the lower packet delivery rate for Scenario 2 is not caused by HDARP not being able to find a route that is free from leakage risks. The very low number of leaked packets for HDARP (see Figure 6) shows that HDARP was indeed able to find leakage-free routes in (virtually) all cases. The type of destructive interference mentioned here can be handled in the future by smart antenna arrays that multiplex multiple signals over time, frequency and angle of arrival. Figure 7: Average packet life time in seconds (99% confidence interval) when using omnidirectional antennas for all protocols except HDARP (HDARP uses directional antennas) for Scenario 1 (**upper**) and Scenario 2 (**lower**). In MANETs, there are two types of packets: packets containing user information (the payload provided through UdpBasicApp), e.g., voice communication between pilots and packets containing control information about the network and the network topology (i.e., routing messages). For each of our two scenarios, the number of packets containing user information is the same for all communication protocols. The number of packets containing control information, however, differs between different protocols. Figure 9 shows the total number of packets sent for the protocols considered here. The figure shows that DSR-UU and OLSR send a smaller number of packets than the HDARP protocol and that DSDV sends almost the same amount of packets for our two scenarios. This means that for HDARP, the number of packets containing control information is relatively small compared to most of the other protocols. For HDARP, the control information consists of SA data, and SA data are something that the pilots need for tactical reasons regardless of which communication protocol is used. This means that the control information needed for the HDARP protocol needs to be distributed between the aircraft anyways. As a consequence, Figure 9 does not give a completely fair picture of the number of packets sent, since the values for the other protocols do not include communication of SA data. In Table 1, we see that the average time between UDP datagram transmissions is 150 milliseconds (uniform (0.1, 0.2)) and that the  
Figure 8: Average number of packets sent over the radio interface (99% confidence interval) when using omnidirectional antennas for all protocols except HDARP (HDARP uses directional antennas) for Scenario 1 (**upper**) and Scenario 2 (**lower**). average time between SA update messages is 4 s (uniform (3, 5)).