## 7 Classification of Mobile Sink based Data Collection Schemes
### Controlled Sink Mobility-Based Schemes
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline Date & \multicolumn{2}{c}{Shift-Modifieds} & No. of & Date & Reporting & Networks & Overliest & Estimated & \\ Collection & \multicolumn{2}{c}{Convention} & \multicolumn{2}{c}{Smoke} & \multicolumn{2}{c}{Mote} & \multicolumn{2}{c}{Architecture} & \multicolumn{2}{c}{Prediction} & \multicolumn{2}{c}{Prediction} & \multicolumn{2}{c}{Prediction} \\ \hline
**Objective** & \multicolumn{2}{c}{Convention} & \multicolumn{2}{c}{Smoke} & \multicolumn{2}{c}{Mote} & \multicolumn{2}{c}{Architecture} & \multicolumn{2}{c}{Prediction} & \multicolumn{2}{c}{Prediction} \\ \hline
**DDRP** & \multicolumn{2}{c}{} & & & & & & & \\
**[33]** & No constraints & Multiple & Periodic &
\begin{tabular}{c} Homogeneous nodes \\ deployment \\ \end{tabular} & Overhearing mechanism & Low & Prolonging network lifetime \\ \hline
**[35]** & No constraints & Single & \
\begin{tabular}{c} Proactive and \\ Reactive \\ \end{tabular} &
\begin{tabular}{c} Homogeneous nodes \\ deployment \\ \end{tabular} & Nodes within a confined zone & \multirow{2}{*}{Medium} & \multirow{2}{*}{Prolonging network lifetime} \\ \hline
**[36]** & No constraints & Single & Reactive &
\begin{tabular}{c} Homogeneous nodes \\ deployment \\ \end{tabular} & Not Specified & Medium & Prolonging network lifetime \\ \hline
**ILSR** & \multicolumn{2}{c}{} & & & & & \\
**[37]** & No constraints & Single & Proactive &
\begin{tabular}{c} Homogeneous nodes \\ around the sink are only informed \\ \end{tabular} & Low & Guaranteed message delivery \\ \hline
**[39]** & No constraints & Single & Reactive &
\begin{tabular}{c} Homogeneous nodes \\ deployment \\ \end{tabular} & Not Specified & Medium & Prolonging network lifetime \\ \hline
**[7]** & No constraints & Single & Proactive & \
\begin{tabular}{c} Homogeneous nodes \\ deployment \\ \end{tabular} & Overhearing mechanism & Low &
\begin{tabular}{c} Guaranteed data delivery \\ with minimal network \\ control overhead \\ \end{tabular} \\ \hline
**DEEP** & \multicolumn{2}{c}{} & & & & & \\
**[41]** & No constraints & Single & Proactive & \
\begin{tabular}{c} Homogeneous nodes \\ deployment \\ \end{tabular} & Not Specified & Low &
\begin{tabular}{c} Improving network \\ lifetime while minimizing \\ the hardware cost \\ \end{tabular} \\ \hline
**TTDD** & \multicolumn{2}{c}{} & & & & & \\
**[42]** & No constraints & Multiple & \
\begin{tabular}{c} Query driven and \\ Proactive \\ \end{tabular} &
\begin{tabular}{c} Homogeneous nodes \\ deployment \\ \end{tabular} & Sinks update only old neighbors & Medium & Improving network lifetime \\ \hline
**SEAD** & \multicolumn{2}{c}{} & & & & & \\
**[44]** & No constraints & Multiple & Query driven &
\begin{tabular}{c} Homogeneous nodes \\ deployment \\ \end{tabular} & Sink updates only old neighbors & Medium & Improving network lifetime \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of path unconstrained based data collection schemes. To avoid collisions if there are too many transmissions, the process is interrupted and a schedule is adopted when the mobile sinks arrive at the CHs. The proposed scheme reduces message delivery latency by employing several mobile sinks operating simultaneously in various segments of the sensor field thereby reducing the waiting time of nodes to deliver their sensory data to the sinks. However, the use of multiple mobile sinks limits its applicability to certain applications only. Furthermore, direct communication of the mobile sinks with the sensor nodes or only via the single-hop CHs may not be feasible in certain situations such as in battlefields or forest environments. [PERSON] _et al._ proposed a method for energy-efficient and latency-aware data collection in mWSNs that exploits biased sink mobility with adaptive stop times [12]. It is based on the idea that due to sink mobility, certain nodes may not complete their data reporting to the sink and thus have to wait for the sink's next trip. This results in high data delivery latency and potential message losses.