## 5 Performance Evaluation
### Case Study: Wi-Fi Power Savings by LDWuR
#### 5.1.3 Performance Comparison  
Figure 9a shows the comparison of our WuR with existing WuRs [5,20] in terms of received power consumption and free-space distance [33]. To wake up the IEEE 802.11-compliant data radio, WuR is required to have a similar communication range as the IEEE 802.11-compliant radio. To save the IEEE 802.11-compliant radio's power consumption, the required power consumption of WuR is lower than the IEEE 802.11-compliant radio. For the received power consumption, all WuRs' power consumptions support sufficiently low power consumption. For the free-space distance, some WuRs support a sufficient communication range. Especially, our WuR performs with the best communication range among existing WuRs with the proper power consumption. The short-range WuR leads to a high-density deployment. This means that it requires more maintenance cost.  
Figure 9b shows the latency comparison with existing WuRs [5,20] with various beacon intervals. Our WuR with sp has a similar latency as existing WuRs. As our design considers PERs and expected transmission times of our WuR and IEEE 802.11-compliant data radio, our WuR's latency increases. However, existing WuRs do not consider the PER and expected transmission time. Thus, they have shorter latency than our WuR. As the latency of the work [5] depends on the backoff time duration, we adopt the average latency of half a beacon interval to estimate it.  
Figure 9: Performance comparison of our LDWuR with existing WuRs. (**a**) Received power consumption _versus_ free-space distance; (**b**) latency _versus_ beacon interval.  
We adopt our WuR [24] as a basic module with directional and omnidirectional antennas for static and dynamic strategies, respectively. The power consumption and latency of our basic module are described in the previous work [24]. Our basic module's total power consumption is the same as the average total power consumption of static and dynamic strategies. The latencies are \(N_{dir}\) times and \(N_{dir}^{beam}\) times our basis module's total latency for static and dynamic strategies, respectively.  
In the performance evaluation section, the power consumptions in Figures 6(a) and 7(a) include the power consumptions of our WuR. The power consumption of our WuR is \(27.6\,\mathrm{mW}\), while the listening power consumption of the IEEE 802.11-compliant radio is \(223.2\,\mathrm{mW}\)[31, 34]. We adopt the average total power consumption of static or dynamic antennas to evaluate performances. The probabilities of our WuR with packet error and the data radio with packet error are considered in Equation (15). The false wake-ups or missed wake-ups are discussed in cases 1a and 1b, respectively [24]. To compare the communication ranges of our WuR and IEEE 802.11-compliant radio, we adopt the sensitivity characteristic of our WuR and IEEE 802.11-compliant radio, as the communication range depends on the environments. Our WuR's sensitivity is \(-122\,\mathrm{dBm}\), while the IEEE 802.11-compliant radio's sensitivity is \(-90\,\mathrm{dBm}\) for the IEEE 802.11b standard [5]. In free space path loss conditions, our WuR performs a long-range communication of about \(1\,\mathrm{km}\), which is better than the IEEE 802.11b-compliant radio.  
For the Wi-Fi data communication range of 802.11b (sensitivity level of \(-90\,\mathrm{dBm}\)) [5], our WuR supports \(-122\,\mathrm{dBm}\)[24], which is sufficient to cover the Wi-Fi data communication range. The existing study [20] proposes a WuR with a sensitivity of \(-52\,\mathrm{dBm}\). However, the sensitivity cannot cover the entire Wi-Fi data communication range, which limits the operational range.