## 2 Related Works
### Geographic Routing
#### 2.1.2 Receiver-Based Geographic Routing Algorithms  
Existing receiver-based underwater routing algorithms using geographic information for routing are; depth-based routing (DBR) [16], delay sensitive DBR (DSDBR), hop-by-hop dynamic addressing based (H2-DAB) [19], etc. In DBR, greedy forwarding is used to find out higher depth node. This approach leads to immutable nomination of forwarder resulting in energy hole creation. In DBR, depth information is used instead of location information, therefore, multiple nodes transmit the same packet that results in high energy depletion and collisions at receiver side [16]. The extended version of DBR was energy efficient DBR (EEDBR), in which energy was also considered for forwarder selection along with the depth to avoid immutable nomination of the forwarder node [17]. In [18], another variation of DBR that formulates holding time calculations to reduce latency in the network. H2-DAB [19] uses two part information: node ID and hop ID for routing the data packet. This protocol is energy efficient because it does not store complex routing information in routing tables. Anyhow, it is needed to update routing table on time for effective data transmission.  
To avoid horizontal communication between same depth sensor nodes, DVPR opts triangular inequality theorem. According to that, same depth nodes are avoided using coordinate information of participating nodes in communication. However, accurate position information is a challenging task itself [20]. Considering this shortcoming, authors proposed self-adaption algorithm based on position information of sender node and receiver node with respect to virtual vector in a virtual pipeline. According to this information, suitableness of a node is calculated for routing the data towards destination [21].  
Another objective aimed to achieve in our work is maximum coverage over the monitoring network region. We have performed multiple sink positioning in the way to attain our objective up to the maximal extent. Because sinks are mechanically driven devices and a specific cost is associated with them. Concerning to that, we have tried to minimize the total travelled distance of sinks deployed in three dimensional field. Such distance constrained problem is addressed in [22], in which sinks time profile is monitored. Additionally, sum of all sinks time profile is observed and based on that scheduling is made for the selected sink for sink location. In another contribution [23], authors performed formulation based on predetermined routing paths and the variable pause times for lifetime optimization.  
In [5], the authors proposed depth adjustment techniques known as GEDAR for void node recovery in UWSNs. In this scheme, winch-based apparatus is used for depth adjustment of void node in vertical direction. Further, with the depth adjustment, the greedy forwarding approach is resumed. Additionally, when void node occurs, the fall recovery procedure is used to discover an alternate path for delivering data successfully. However, if alternate route is not available in that case, depth of the node is adjusted to resume the communication among the network nodes.