## 4 Performance Evaluation
### Numerical Results  
In this section, we present the analysis and experimental results of the two models. Detailed parameter specification is given in Table 1. Other parameters are set to the default values of the TOSSIM simulator radio model for CC2420, inherited from our previous work [3]. To measure the duty cycle, we record changes in the radio's states and use a counter to accumulate the time period used in each state. Figure 2 shows average duty cycle results in various request interval values. While the duty cycle result of the location-based model highly depends on the request interval value, that of the periodic model is independent to the request interval. In the periodic model, sensors keep reporting their sensing data regardless of whether or not there are demands. On the contrary, energy consumption in the location-based model is proportional to the request frequency of mobile users. When there are high demands (i.e., short request interval), sensors have to transmit their sensing data more frequently. Therefore, higher duty cycle results are observed. If a high frequency of requests is sent (i.e., request interval of 10 s), average duty cycle of the location-based model is even higher than the periodic model (i.e., with periodic interval of 20 s). In this case, using a periodic model may be more beneficial in terms of energy consumption for sending requests. When the request interval increases, average duty cycle result of the location-based model is inversely proportional. At the request interval of 30 s, duty cycle result of the location-based model is considerably lower than that of the periodic model. After that, the average duty cycle result of the location-based model significantly drops to around 3% when the request interval is increased to 6 min, compared to 8% of the periodic model. Figure 3 presents the performance behavior of the two models under different average cluster sizes--in other words, under different correlation levels of sensing data among nodes. In the periodic model, every node periodically reports its data to the cloud without knowing there are demands or not. In the location-based model, the cloud plays a role as the controller who controls which nodes are required to report their data under specific requests of mobile users. Therefore, the cloud can reduce data redundancy by minimizing the number of nodes that produce similar sensing data required to report their data at the same time. In this way, the model can achieve more energy savings compared to the periodic model under equivalent conditions (i.e., request interval, packet size, low power listening \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline Data packet length & 32 bytes & Nodes & 100 \\ Carrier sensing & 2.5 ms & Sensing & 2 ms \\ \(l_{W}^{WSN}\) & 0.5 s & \(l_{S}^{WSN}\) & 10 s \\ \(l_{W}^{gering}\) & 0.25 s & \(l_{S}^{gering}\) & 1 s \\ \(l_{W}^{quiet}\) & 1 s & \(l_{S}^{quiet}\) & \(\infty\) \\ \(\Theta\) & 1–5 & \# of apps & 1–5 \\ \(I_{request}\) & 10 s–10 min & \(T_{request}\) & 4 s \\ \(h\) & 5 & \# of nodes & 126 \\ \(\rho\) & 0.5 & \(T_{pkt}\) /byte & 0.032 ms \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Parameters. Figure 2: Average energy consumption under various request intervals. mode, etc.). Energy efficiency of the location-based model is proportional to the average cluster size. At a cluster size of 1, the two models witness a small difference in the average duty cycle results. The energy efficiency of the location-based model is increased significantly when we increase the average cluster size from 1 to 3. This result indicates that the location-based model is more effective in cases of dense network deployment with high redundancy. Figure 4 provides how much improvement in terms of the network lifetime that the location-based model achieves compared to the periodic model. Note that the network lifetime in this paper is defined as the lifetime of the network until there is at least one node out of battery.