## 2 Related Works
### Algorithms Using Localization  
In the context of algorithms using localization, it is expected that each sensor node has location information about itself and sinks using GPS that helps to identify the next forwarding nodes toward the sink. The critical point of all localization algorithms is to use location information for the forwarding process. However, it has significant variations in its method of identifying the best sensor toward the sink. Algorithms using localization look at different shapes between the sink and sensor node to determine the next forwarding nodes such as cone, layer, virtual pipeline, and zone toward the sink. The following paragraphs discuss some well-known algorithms using localization.  
The authors in [32] proposed a localization routing method named the vector-based forwarding protocol (VBF). The presented approach focuses on solving the problems in the UWSNs (i.e., robustness, scalability, and energy-efficiency). The VBF protocol selects the next nodes based on using fix virtual pipeline from the sender toward the destination. Any sensor node located inside the virtual pipeline is elected as a next-hop, and the rest nodes are discarded. Nevertheless, VBF suffers from significant drawbacks. The full positioning information is required for each sensor node and the performance is influenced by the unavailability of sensors at the predefined radius in sparse networks.  
The authors in [33] provided a new version of VBF by developing hop-by-hop vector-based forwarding (HH-VBF). This scheme utilizes a simulated pipeline from the sender node to the sink with a fixable pipeline regarding the location of the nodes that is improving the process of electing the next-hop node. Each sender node initializes a pipeline independently to send the data packet. Like VBF, the delivery ratio is increased, and energy consumption is dramatically decreased. Furthermore, the employment of positioning information becomes the core drawback of HH-VBF because of the inevitability of GPS in underwater areas.  
In addition, vector based void avoidance (VBVA) is another improvement of VBF that employs the principles of HH-VBF regarding electing the next-hop nodes without using energy nor reliable parameters [34]. The main variance between VBF, HH-VBF, and VBVA is that VBVA employs dual 3-D flooding techniques to avoid the empty areas, named vector-shift and back-pressure.  
Another routing protocol called focused beam routing (FBR) on a cross-layer location-based has been presented by [35]. The FBR protocol selects the next forwarding node by utilizing different transmission power-levels. In the routing process, the sender sends a Request to Send (RTS) data packet to the neighbor's transmission power-level. Whenever the sender receives the Clear to Send (CTS) packet from the neighbor, the data packet will send to the source of the CTS packet. In case the sender does not receive any CTS from its neighbor, the transmission power-level is raised to the next power-level. This process is frequently repeated until the CTS message is received successfully. However, the frequently repeated process and exchanging the RTS and CTS messages will lead to delay. Furthermore, the FBR suffers from the localization problem.  
On the other hand, a non-location routing protocol has been conducted by [36] named the power-efficient routing protocol (PER), taking the energy consumption as the main contribution. The basic idea is that the sink node is positioned in the midpoint area, the rest nodes are deployed randomly in the transmission area, and the sender is placed at the bottom level of water. Based on the calculated angle between neighbor nodes, residual energy, distance to the sink, and the source node selects the optimal two neighbors.