# Hardware Mechanism for Energy Saving in WiFi Access Points
## 4 Discussion  
In previous sections we explained the power consumption for \(T_{c}\) and \(T_{d}\) in order to show the complexity to calibrate \(w\) parameters of our model. In this Section we analyze the power consumption in WiFi AP (using our mechanism or not) in one cycle (\(k=1\)) taking into account the power consumed in \(T_{c}\) and \(T_{d}\). Then we project our results to infer the energy saving for greater values of \(k\).  
We always obtained (in all the implemented test) that \(T_{d}>T_{c}\). In test OBTx-1 we obtained a difference of 3 h (7 h 30 m \(>\) 4 h 30 m), and in test OBTx-2 we obtained 1 h 8 m (6 h 8 m \(>\) 5 h 0 m). Moreover, we showed in Section 2.1 that if \(w_{v}>w_{c}\) then \(T_{d}>T_{c}\), and in that case energy saving could be achieved. In Section 3 we showed \(w_{c}=3.25\) and \(w_{v}=3.24\) and \(T_{d}>T_{c}\) for both tests. So, according to our formal model, energy saving in one cycle (\(k=1\)) was achieved. Let us now show a power consumption analysis, in one cycle (\(k=1\)), using and not using our mechanism. Figure 12 shows that in a period of 12 h (OBTx-1) or 11 h (OBTx-2), we obtained a difference of 268 W and 465 W. Although, not a high amount of energy was saved, our model was satisfied.  
Figure 11: (**a**) Evolution of \(V_{d}\) and \(I_{d}\) in time. (**b**) Evolution of power consumption in time (\(T_{d}\)).  
Analyzing the charging process of isolated battery versus the charging and discharging cycles of the battery using our mechanism we obtained several learn lessons:  
* The vacuum voltage should be as high as posible. This allows to augment the slope of \(I_{c}\) during \(T_{c}\). Which means that a constant \(I_{c}\) will be obtained earliest. In this way we enfoster the shortening of \(T_{c}\).
* Starting the discharge period, the \(V_{d}\) must be as high as possible and the slope of Id be as small as possible. This enfoster to extend \(T_{d}\).
* In both previous cases, if the WiFi AP works very little, we enfoster the shortening of \(T_{c}\) and extension of \(T_{d}\).  
Let us reason about the above results in a day of a typical official organism like a government building (\(k=2\)). Usually, it has normal activity from 7 h to 17 h in a day (10 h approximately). During that time the WiFi APs can be active transmitting data. But in the rest of the day (from 17 h 01 m to 6 h 59 m) the WiFi APs will be inactive only transmitting beacons (14 h approximately). Thus, we have a margin of hours in a day to make work our Mechanism for energy saving. That is, in that period of time of 14 h, around 6 h the WiFi AP will not consume energy of the PSE. This is because the battery is charged with no extra power consumption from PSE.  
For greater values of \(k\) we can use a simulation based on WoS starting from our experimental values of \(T_{c}\) and \(T_{d}\). That analysis will inform us about the probability to save an estimated amount of energy (W). We think it is more interesting to scale the energy saving of two cycles (\(k=2\)) per day, for example in one month (directly expanding it to a bigger amount of time). Figure 13 shows the scaled energy saving in a month that will reach 28.8 KW, which is very convenient because it could save 345.6 KW annually for each AP in operation. In a typical medium-size government building, with around 50 WiFi AP, the energy saving would be considerable.  
A final remark about the optimization of energy saving derived from our formal model is made. This remark has been exposed also in the experimental results previously presented. The \(T_{c}\) can be minimized if the \(I_{c}\) will be minimized and vacuum voltage of the battery will be maximized when adjusting properly the implied parameters (\(w\)). The \(T_{d}\) can be maximized if the battery voltage remains greater than a voltage threshold.  
Figure 12: Comparison of power consumption in one cycle (\(k=1\)) with and without our mechanism.  
Figure 13: Scaling energy saving of a day (\(k=2\)) in a month (\(k=62\)).