# SOBER-MCS: Sociability-Oriented and Battery Efficient Recruitment for Mobile Crowd-Sensing
## 5 Performance Evaluation
### Simulation Results  
The simulation results aimed at evaluating the impact of introducing sociability-orientation and energy-awareness to the baseline solution. We considered three different scenarios for the residual energy threshold (\(E_{\theta}\)) where the threshold was set to either of the following values in each scenario: 10%, 15% and 20%. Figure 9 depicts the platform utility by comparing four different scenarios: the MCS benchmark (i.e., MSensing), SOBER-MCS (Sociability-Oriented and Battery-Efficient Recruitment for Mobile Crowd-Sensing) with the residual battery level threshold of 10%, SOBER-MCS with the residual battery level threshold of 15% and SOBER-MCS with the residual battery level threshold of 20%. With the increasing task arrival rate from 20-100, the platform utility increases under each recruitment scheme as a result of the increase in the quantity (and consequently, the value) of the data. Under very \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Terrain size & \(1000\times 1000\) \\ Sensing range & 30 units \\ Timeslot duration & 30 min \\ \hline Number of users & \((1000)\) \\  & Highly-active users \((54\%)\) \\ Initial charge & Moderately-active users \((58\%)\) \\ of the battery & Least active users \((63\%)\) \\ \hline Value of sensing costs & \([1-10]\) \\ Task duration & Uniformly distributed in \([1,5]\) min \\ Task arrival rate & \((20,40,60,80,100)\) tasks\(/\)min \\ Residual energy threshold \((\Re)\) & \((10\%,15\%,20\%)\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulation settings. lightly arriving task patterns (i.e., 20 tasks/min), SOBER-MCS with the residual energy threshold level of 10% can introduce over a 14-times improvement to the performance of MSensing. When the residual battery level threshold is set to 15%, the improvement can reach up to 20%. Finally, setting the residual energy threshold to 20% can improve the platform utility of the benchmark by >26%. These improvements follow almost a constant behavior under all sensing task arrival times. For instance, under the very heavy task arrival rate of 100 tasks/min, over 50% improvement in platform utility can be achieved when the residual battery level is set to 20%. The improvement is basically achieved by the introduction of energy-awareness (i.e., awareness of the residual battery level of the participating smartphone) to the recruitment strategy allowing one to exclude the devices that are likely to die (i.e., \"breakout phones\" as termed in this paper) before the completion of the sensing campaign. The only exception in the improvement of platform utility is under the case where the task arrival rate is 80 tasks/min and the residual battery level is set to 10% in the SOBER-MCS strategy. In the absence of a feasible solution to address the platform-user utility trade-off, the proposed recruitment strategy is expected to favor user utility against platform utility since the same number of tasks is covered by less participants. While this is mostly related to the uniform nature of the user distribution over the terrain, Figure 10 supports the behavior explained above with significantly higher user utility. A closer glance at Figure 10 reveals the competent behavior of the proposed recruitment strategy, namely SOBER-MCS. As a result of the conflicting nature of the participants and the platform, it is  
Figure 10: Average user utility. Figure 9: Platform utility. SOBER-MCS, Sociability-Oriented and Battery-Efficient Recruitment for Mobile Crowd-Sensing. almost inevitable to sacrifice either platform utility or user utility to introduce a significant increase in the other performance metric. However, as seen in the figure, the proposed approach does not lead to any decrease in user utility. On the contrary, under extreme load levels (i.e., 20 tasks/min and 100 tasks/min), setting the residual battery level threshold to 20% can further improve average user utility by roughly 5%.