## 4 Simulation Evaluation
### Comparison with Other Methods
#### 4.3.1 Result in the Fixed Sink Scenario  
Figures 7-9 show the simulation results of the four methods for each metric in the fixed sink scenario. As shown in Figure 7, SC-Sched(simple) without retransmission mechanisms has a very low \begin{table}
\begin{tabular}{c|c|c c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Number of** \\ **Nodes** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Number of Data** \\ **Collection Points** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Frame Delivery** \\ **Ratio (\%)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Total Energy** \\ **Consumption (J)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Maximum** \\ **Energy** \\ **Consumption (J)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Network** \\ **Lifetime** \\ **(day)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Improvement** \\ **in Network** \\ **Lifetime (\%)** \\ \end{tabular} } \\ \cline{1-1} \multirow{3}{*}{100} & 1 & 99.6 & 184.2 & 2.39 & 4217.2 & - \\ \cline{1-1}  & 2 & 99.8 & 184.2 & 2.15 & 4653.8 & 10.4 \\ \cline{1-1}  & 3 & 99.9 & 184.2 & 2.07 & 4832.8 & 14.6 \\ \cline{1-1}  & 4 & 99.8 & 184.2 & 2.02 & 4948.3 & 17.3 \\ \hline \multirow{3}{*}{200} & 1 & 99.6 & 368.0 & 2.57 & 3922.8 & - \\ \cline{1-1}  & 2 & 99.8 & 368.1 & 2.26 & 4429.5 & 12.9 \\ \cline{1-1}  & 3 & 99.8 & 368.1 & 2.15 & 4662.0 & 18.8 \\ \cline{1-1}  & 4 & 99.8 & 368.1 & 2.07 & 4824.1 & 23.0 \\ \hline \multirow{3}{*}{300} & 1 & 99.6 & 552.0 & 2.75 & 3687.7 & - \\ \cline{1-1}  & 2 & 99.8 & 552.0 & 2.35 & 4266.6 & 15.7 \\ \cline{1-1}  & 3 & 99.9 & 552.0 & 2.20 & 4551.5 & 23.4 \\ \cline{1-1}  & 4 & 99.9 & 552.0 & 2.12 & 4726.6 & 28.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Evaluation of SC-Sched in the mobile sink scenario. \begin{table}
\begin{tabular}{c|c|c c c c} \hline \hline \multirow{2}{*}{\begin{tabular}{c} **Number of** \\ **Nodes** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Multiple** \\ **Channels** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Frame Delivery** \\ **Ratio (\%)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Total Energy** \\ **Consumption (J)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **Data Collection** \\ **Time (s)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **Reduction** \\ **Ratio (\%)** \\ \end{tabular} } \\ \hline \multirow{2}{*}{86} & None & 99.1 & 0.27 & 6.2 & \multirow{2}{*}{33.9} \\ \cline{2-2} \cline{4-6}  & Use & 99.1 & 0.27 & 4.1 & \\ \hline \multirow{2}{*}{196} & None & 99.7 & 0.54 & 13.8 & \multirow{2}{*}{38.4} \\ \cline{2-2} \cline{4-6}  & Use & 99.8 & 0.52 & 8.5 & \\ \hline \multirow{2}{*}{400} & None & 99.4 & 1.20 & 27.9 & \multirow{2}{*}{31.2} \\ \cline{2-2} \cline{4-6}  & Use & 99.4 & 1.11 & 19.2 & \\ \hline \multirow{2}{*}{600} & None & 99.4 & 1.94 & 41.8 & \multirow{2}{*}{31.6} \\ \cline{2-2} \cline{4-6}  & Use & 99.4 & 1.75 & 28.6 & \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Evaluation of using multiple channels. frame delivery ratio, about 60%, which confirms the necessity of adopting retransmission mechanisms in SC-Sched. As shown in Figure 8, the total energy consumption of SC-Sched is much lower than that of WuR-TDMA and ContikiMAC. In WuR-TDMA, receiving from the sink node the information of each node's routing by the communication module causes much overhead, so the active time of all sensor nodes is prolonged and total energy consumption increases. In ContikiMAC, there are four overheads that affect active time. First, the sender uses CSMA/CA and it is necessary to wait for a random backoff time before actual transmissions. Second, the sender repeats transmission of the data frame until an ACK is received from the receiver. Third, a surrounding node, in its active period, may overhear a data frame not addressed to itself. Finally, each sensor node needs to wake up periodically by duty cycling. In comparison, SC-Sched achieves much lower power consumption by removing all of these overheads.