# A Cooja-Based Tool for Coverage and Lifetime Evaluation in an In-Building Sensor Network+
## 6 Performance Evaluation
### One Room  
In the TMON deployment, there are 22 sensor nodes in one room. Figure 9 shows TMON's global quality of coverage. When all nodes are active, the network can only maintain the desired QoC with a 95% local coverage threshold for 150 time units. With greedy-maintain and local-maintain, the lifetime can be increased up to around eight times as their percentages of QoC do not fall below the threshold before 1195 time units. The increased lifetime is calculated by dividing the lifetime of the network with an algorithm by the lifetime when all nodes are active. The details for the lifetime improvement are summarised in Table 7, where greedy-maintain and local-maintain achieve 8.39 and 7.99 times lifetime improvement, respectively. Greedy-maintain achieves a longer lifetime compared to local-maintain, as it requires less nodes to be active to cover the room (see Figure 10). In cases where the percentage of active nodes increases in this figure, that is due to redundant nodes being turned on to repair the coverage when a node dies.  
Using the dataset from TMON, there is only a slight additional improvement in the lifetime of the network when the reading correlation is utilised, _i.e._, 8.43 times for greedy-maintain with correlation and 8.04 times for local-maintain with correlation. This happens as the temperature variations in the data centre room is very high. Figure 11 shows the percentage of dead nodes over time, where the localised algorithm has more dead nodes compared to the greedy one. In the TMON deployment, all nodes are within a one-hop distance from the sink. Therefore, when a node dies, no other nodes will be disconnected from the network. The percentages of active and dead nodes when the simulation finished are summarised in Table 7. Greedy-maintain with reading correlation has 45.45% of nodes still active when the simulation finished, but can only support 77.43% QoC. Local-maintain with reading correlation has 13.64% active nodes for 54.51% QoC.  
The average execution time for each node with greedy-maintain, local-maintain, greedy-maintain with correlation and local-maintain with correlation are 0.0164, 0.0151, 0.0203 and 0.0197 time units, respectively.  
Figure 11: TMON’s percentage of dead nodes over time.  
\begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Algorithm** & \begin{tabular}{c} **Lifetime** \\ **(time units)** \\ \end{tabular} & \begin{tabular}{c} **Increased** \\ **Lifetime** \\ \end{tabular} & \begin{tabular}{c} **Active** \\ **Node** \\ \end{tabular} & \
\begin{tabular}{c} **Dead** \\ **Node** \\ \end{tabular} &
\begin{tabular}{c} **QoC** \\ **Node** \\ \end{tabular} \\ \hline All nodes active & 150 & - & 4.55\% & 95.45\% & 20.83\% \\ Greedy-maintain & 1258 & 8.39\(\times\) & 40.91\% & 59.09\% & 62.85\% \\ Local-maintain & 1198 & 7.99\(\times\) & 13.64\% & 86.36\% & 49.31\% \\ Greedy-maintain + correlation & 1265 & 8.43\(\times\) & 45.45\% & 54.55\% & 77.43\% \\ Local-maintain + correlation & 1206 & 8.04\(\times\) & 13.64\% & 86.36\% & 54.51\% \\ \hline \hline \end{tabular}
\end{table}
Table 7: TMON’s simulation results.  
Figure 10: TMON’s percentage of active nodes over time.  
Figure 9: TMON’s global quality of coverage.