# Value of Information Based Data Retrieval in UWSNs
## 5 Performance Measures, Simulation Setup and Results
### Results
#### 5.3.5. Response to Emergency  
The basic reason to employ VoI was to have a mechanism to distinguish between higher and lower priority situations in an organic fashion, thus enabling a more appropriate response to the situation. The greedy and hybrid algorithms were designed to address high-priority situations such as emergencies. Here, we look at some measures that shed light on how the various pathplanners perform under emergency. Again, all results are described with respect to RPP in terms of percentage improvement in performance. The results are shown in Figure 8. We vary \(N_{HS}\) from 1 to 10 hot-spots. We record percentage improvement in VoI accumulated from first hot-spot (\(v_{HS_{ACC}}\%\uparrow\)), percentage reduction in VoI lost at first hot-spot (\(v_{HS_{1}}\%\downarrow\)), percentage reduction in tour time to first hot-spot (\(\tau_{HS}\%\downarrow\)) and the normalized urgency score (\(\dfrac{\Psi_{PP}}{\Psi_{RPP}}\)). The percentages are calculated with respect to the RPP path planner performance:  
\[v_{HS_{ACC}}\%\uparrow =\dfrac{v_{HS_{ACC}}}{v_{HS_{ACC}}^{RPP}}\times 100 \tag{34}\] \[v_{HS_{L}}\%\downarrow =\dfrac{v_{HS_{L}}}{v_{HS_{L}}^{RPP}}\times 100\] (35) \[\tau_{HS}\%\downarrow =\dfrac{\tau_{HS}}{\tau_{HS}^{RPP}}\times 100\] (36) \[\dfrac{\Psi_{PP}}{\Psi_{RPP}} =\dfrac{S_{I}}{S_{P}}\times\dfrac{S_{P}^{RPP}}{S_{I}^{RPP}} \tag{37}\]  
GPP and HPP are best when it comes to accumulating VoI from the first hot-spot. GIPP and HIPP follow closely in terms of performance but the gap widens with increasing \(N_{HS}\). The reason, as discussed earlier, is that the intermediate path planners start to hit lesser valued hot-spots on their way to the highest valued hot-spot. As an intermediate lesser valued hot-spot maybe encountered first by the AUV, therefore, \(v_{HS_{ACC}}\) performance should decrease. In terms of \(v_{HS_{L}}\), GPP and HPP are better for \(N_{HS}=1\) or 2. For \(N_{HS}\geq 3\), GIPP and HIPP start performing better, i.e., they avoid a higher loss in terms of VoI from the first hot-spot encountered. The reason is the same as stated above, i.e., they encounter other hot-spots on the tour while traveling towards the highest-priority one. Because, hot-spots are encountered earlier, therefore, the respective VoI loss \(v_{HS_{L}}\) at that node should be lower. This phenomenon of encountering hot-spots earlier than planned can be verified from the time to arrive at the first hot-spot \(\tau_{HS}\) results. These results for \(\tau_{HS}\) follow exactly \(v_{HS_{L}}\) in character. Again, GPP and HPP perform better for \(N_{HS}=1\) or 2, while for \(N_{HS}\geq 3\), GIPP and HIPP are better. This thus corroborates the speculation that hot-spots are being encountered earlier by path planners that are based on the intermediate node visitation strategy. The urgency measure \(\Psi\) sheds light on response to an emergency. This is because it generates a score based on the sequence of visitation to the hot-spots. It encodes, that how much priority was maintained while visiting the nodes. GPP and HPP have the highest urgency score. This is because they visit the nodes in the exact order of descending priority as dictated by VoI advertised. The intermediate node visitation algorithms, GIPP and HIPP, come in second. This is expected as intermediate nodes are being attended to en-route to the highest-priority node. The performance gap widens between algorithms with or without intermediate node visitation with an increasing \(N_{HS}\). The performance of LPP is as worse as RPP throughout the \(N_{HS}\) range. This is inferred from normalized result value of \(\Psi_{LPP}/\Psi_{RPP}\approx 1\). This shows that GPP and HPP are best for addressing emergencies as they directly go to the highest priority node first. Close in second are GIPP and HIPP. They lose out marginally because of visiting intermediate nodes. LPP has no capacity for dealing with emergencies. Figure 8: Emergency Response w.r.t.