## 2 Related Work
### Energy Efficiency Based  
The works [6; 7; 8; 9] proposed different schemes to enhance the energy-efficiency. The works in [6; 7] have used the multi-hop techniques. Whereas, the paper [6] is focusing on network reliability, mobility management, PDR and energy efficiency. On the other hand, the work [7] is only focusing on energy efficiency. Both works [6; 7] achieve their objectives; however, end-to-end delay is compromised. The authors in works [8; 9] mainly focus on reliability by covering one-hop from the forwarder node. The proposed scheme EBLE from the work [8] aims to minimize the energy dissipation with packet size management. The objective is successfully achieved on the cost of delay. The cooperative routing is used in work [9] for data reliability and mobility management, while PDR and efficient energy usage are the main aims. The objectives are achieved successfully; however, the network performs poorly in sparse network deployment. The works [10; 11; 12; 13] are also using energy efficiency techniques. The works [10; 12] provide the reliability. Both of works discuss the concept of multi-hoping. The proposed scheme in the work [10] is beneficial for a large amount of data packets; however, this proposed technique does not perform well in sparse network deployment. The MLPR from [12] looks toward the efficient path for routing by using minimum energy. For the implementation of MLPR, more memory is required for the extra operations at each node. The energy dissipation schemes; SDVF and EBULC are proposed in works [11; 13], respectively. Both schemes consider mobility management for decreasing the energy consumption in UWSNs. Results show that end-to-end delay in the works [11; 13] is enhanced. \begin{table}
\begin{tabular}{l l l l l l l l l l l} \hline \hline
**Type of Technique** & **Technique/Protocol** & **Reliability** & **Packet Size** & **Mobility** & **Number** & **Achievements** & **Challenges** & **Limitations** \\ \hline RE-PBR [6] & ✓ & \(\times\) & \(\times\) & \(\checkmark\) & Multi-hop & FDR and energy & Difficult to deploy & In dense deployment, & \\  & & & & & & & efficiency & is & dense network & \\ \hline TCEB [7] & \(\times\) & \(\times\) & \(\times\) & Multi-hop & Less energy & Serious cause of & End-to-end delay is & End-to-end delay is \\  & & & & & & dissipation & energy consumption is & enhanced \\ \hline EBLE [8] & ✓ & ✓ & \(\times\) & Single-hop & Lower energy & Path loss/dead due to & Energy consumption \\  & & & & & & balancing & the continuous data packet & is decreased on the \\  & & & & & traffic load & & transmission & cost of delay \\ \hline Cooperative & ✓ & \(\times\) & ✓ & Single-hop & Successful packet & Wireless sensor nodes & Network \\ routing [9] & & & & & & delivery and & move with current & performance \\  & & & & & & lower energy & & degrades in sparse \\ \hline CS [10] & ✓ & \(\times\) & \(\times\) & Single-hop & Beneficial for & Fewer resources and & Does not perform & effectively in Sparse \\  & & & & & multi-hop & data packets & & network deployment \\ \hline SDVF [11] & ✓ & ✓ & ✓ & ✓ & Single-hop & Increase network & Energy efficiency, & Increase in source to \\  & & & & & & multi-hop & & network complexity & destination delay \\ \hline MLRP [12] & ✓ & \(\times\) & \(\times\) & Multi-hop & Find efficient & Loss of data during & More memory at each \\  & & & & & & path and & transmission process & node is required for \\  & & & & & & minimize energy & & extra operations \\ \hline EBULC [13] & \(\times\) & \(\times\) & ✓ & Multi-hop & Energy efficiency & Complexity of UWSNs & Energy usage is & \\  & & & & & & & minimizes on the cost \\ \hline Energy & \(\times\) & \(\times\) & ✓ & Multi-hop & Energy efficiency & Overhead of routing & Delay is increased \\  & & & & & & enhanced & information and & increase in operational \\  & & & & & & & time & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of different works.