## 4 The Up/Down Mechanism of WiFi MAPs
### Algorithm Specification
Figure 18: Chosen intermediate node for route from node6 to node1 in node6 for 3 HFT sessions of 60 s with node7 WiFi interface deactivation at \(t=10\) and \(t_{DOWN}=4\) s.

#### 6.1.2 Interference Effects

In addition to the previous experiments we have evaluated the effect caused by traffic from external devices to the PWMNS over the same or overlapped channel. Specifically we studied the OLSR interchanged messages. Although shared use of WiFi spectrum is well documented [51], we will analyze the specific case of our test platform. We have configured four different cases:

1. With very spurious signals on adjacent channels out of our control. 2. With an AP on channel 11 (which is adjacent to the channel used on the test platform) and emitting only control frames (especially beacons) which we have called _Interfering_AP_1_. 3. With an AP on channel 11 and another in channel 7 (same channel as our PWMNS configuration) which we have called _Interfering_AP_2_. 4. _Interfering_AP_1_ and _Interfering_AP_2_, but the latter transporting intensive user traffic (using _iperf_[52] application which we consider as interfering traffic for our network). Specifically _Interfering_AP_1_ is an AP-router Belkin model F6D4630-4v1 operating on channel 11, _Interfering_AP_2_ is an AP-router ASUS RT-AC66U Dual Band 3 \(\times\) 3 802.11 ac operating on channel 7. Additionally we used a laptop (ASUS model X552C operating under Ubuntu Linux) and a smartphone (SONY EXPERIA S35 operating under Android). These latter two end-devices were associated to _Interfering_AP_2_ in infrastructure mode, and the laptop acting as an iperf server and the smartphone as an iperf client. Figure 19 shows an image of the latter three devices used in this experiment. In case (a), our PWMNS is less interfered than the other cases. Once captured the OLSR messages detected by every node, we observed their high variability caused by the use of the same channel, hidden nodes and different conditions in the area close to every node. We have highlighted in Figure 20 the origin (in the vertical axis) of the messages detected by node6 respect to the instant (horizontal axis) when they were detected. We have omitted the messages originated by node6. Let us notice the small number of messages from node1 while node4 and node7 transmitted a similar number of them. We could better appreciate the effect on the interchanged messages between the different nodes when there existed other APs or devices emitting on adjacent channels and, specially, on the same channel 7. As we know shared-channel use caused restrictions when packets were emitted which, as consequence, derived in an emission reduction of OLSR messages as well as all other packets. This is shown in Figure 21 as a result of case (d). We have generated that interference traffic starting at instants \(t=10\), \(t=30\) and \(t=50\), and all of them have an approximately duration of 10 s (interference intervals: \(10\leq t\leq 20\), \(30\leq t\leq 40\) and \(50\leq t\leq 60\)). If we compare with Figure 20, we can clearly appreciate that, for the same 60 s session-interval, the number of messages detected by node6 coming from node1, node4 and node7 are fewer; especially those which should have been emitted at instants when _iperf_ made an intensive use of the channel. If we analyse Figure 21 in depth, we corroborate the lack of OLSR messages, especially at instants soon after \(t=10\), \(t=30\) and \(t=50\). Figure 19: Main additional devices which generated interfering traffic. The results for cases (b) and (c) (one single AP on channel 11 for the former; and one AP on channel 11 and another on channel 7 without user traffic) are not showed because they were very similar to case (a) with small variations on the number of detected messages. Our proposal was based on the fact that, when several PWMNS nodes were interfered, OLSR message interchange with the rest of nodes (as well as nodes availability) were affected. The greater amount of external interferences were, the more severely the communication was affected.