## 9 Evaluation
### Channel Interference on Public APs that the Attacker Leverages
#### 9.1.1 Channel  
For public APs that can work in the same public place, in order to avoid channel interference between them, they always work on Channel 1, Channel 6 and Channel 11. Thus, there are six conditions of the channels for two neighbor wireless transmitters, and in this part, the experiments of these six conditions are done to demonstrate that when the channel spacing between two neighbor wireless transmitters is different, the channel interference between them will also be different. In these experiments, the distance between the two neighbor APs is 1 m, and the results are as shown in Figure 7.  
In Figure 7, the value \"0\" on the X-axis means that there exists no channel interference between the safe wireless transmitter and the target public AP; the values \"\(-\)2\" and \"2\" mean that the channel spacing between two wireless transmitters is two; the values \"\(-\)1\" and \"1\" mean the channel spacing between two wireless transmitters is one. \"\(-\)\" means that the channel of the target public AP is less than the channel of the safe wireless transmitter.  
We can see from Figure 7 that the number of received packets is the maximum when there exists no channel interference between the safe wireless transmitters and the target public AP. The number of received packets is relatively low when there exists channel interference between the two wireless transmitters, and when the channel spacing between two wireless transmitters is one, the number of received packets is the minimum and the packet loss rate is the maximum. For example, in Figure 7a,b, when the channel of the safe wireless transmitter is 1 and the channel of the target public AP is 6; if the safe wireless transmitter switches its channel to Channel 5, the packet loss rate is 37.695%; if the safe wireless transmitter switches its channel to Channel 7, the packet loss rate is 45.894%; while if the safe wireless transmitter switches its channel to Channel 4, the packet loss rate is 17.383%; and if the safe wireless transmitter switches its channel to Channel 8, the packet loss rate is 25.392%. Thus, when the channel spacing between the safe wireless transmitter and the target public AP is one, the channel interference between them can achieve the maximum.  
We can see from Figure 7c,d that when there exists no channel interference between safe wireless transmitter and the target public AP, the value of interference strength is the minimum, and the value of the active ratio is the maximum. When the safe wireless transmitter switches the channel, the value of the interference strength will increase, and the value of the active ratio will decrease. When the channel spacing between the safe wireless transmitter and the target public AP is one, the value of the interference strength is the maximum, and the value of active ratio is the minimum. This is consistent with the analysis in Section 8.2.  
Therefore, when the channel spacing between the safe wireless transmitter and the target public AP is one, the channel interference between them is maximum. Thus, the system can switch the channel of the safe wireless transmitter to an adjacent channel of the target public AP, and the channel spacing between them is one.