## 3 Related Work  
The authors in [13] formulated three protocols. The first protocol simply introduced cooperation with the opportunistic pressure routing, in which the source-relay-destination triplet was used to avoid the channel impairments. The second protocol split long paths into small paths when a void- hole existed. The third scheme added cooperation again to the second scheme to counteract channel effects. However, these three schemes suffered from a number of drawbacks. Firstly, nodes were required to know the Euclidean distance information of one another, which is difficult to obtain; especially when the network is sparse, and it also inserts extra delay in the communications. This is because nodes are moved by ocean tides and currents, and it requires constant monitoring of the positions of the nodes. Secondly, constructing shorter paths in sparse networks is almost impossible, as nodes are far apart from one another, at a significant distance. Thirdly, with opportunistic routing, a certain set of nodes constantly participates in data handling. These nodes are near the water surface and are depleted of battery power quickly. This leads to the collapse of the network by halting communications near the water surface. To avoid void-hole and reduce interference, two routing algorithms that incorporate three hop neighbors in data forwarding were presented in [7]. The first protocol works by allowing a source node to construct a path in which sensor nodes are available up to three hops. Then, the source selects a suitable neighbor based on a fitness function, which incorporates the source-neighbor mutual distance, the hop count of the suitable neighbor, and its distance from the sink. In the second algorithm, a suitable neighbor either acts as a unicast or multi-cast node to advance the data further over the most feasible path with respect to the delay. Multi-casting was proposed to overcome channel noise. However, these algorithms require the Euclidean position knowledge of nodes, which is challenging. Furthermore, nodes' operation depends on constant beaconing from the surface sink node, which adds extra delay to the communications. Further, the fitness function adds computational complexity in the algorithm due to the involvement of many parameters for suitable neighbor finding. Furthermore, in sparse networks, the three hop availability of nodes is challenging, and there is no mechanism of avoiding a void-hole when it exists even within the three hops. The authors in [8] devised two protocols to avoid void-hole and achieve reliability in data transfer. Reliability was addressed by opting for low interference paths. The void-hole was avoided by using potential forwarding candidates with complete path connectivity, i.e., from source to sink. However, the computation of the criterion for the potential forwarding candidates was computationally inefficient, as it involved constant beacon messages from the sink node to compute the hop-count and distance from the sink, which also inserted extra delay. In addition, for sparse conditions, the connectivity from the source to sink becomes challenging. The authors in [9] designed two routing schemes. The first scheme modified the virtual pipe, in which nodes transferred information towards the sea surface, in such a manner that every node could make its own pipe for packets' transfer rather than one main pipe for void avoidance. This modifies the usual approach of defining a main pipe for data transfer, which is not always feasible; especially if more nodes lie outside the pipe. The second scheme added cooperative routing to the first scheme to ensure reliability in packets' transfer. However, construction of a pipe in an adaptive manner makes use of geographical coordinates of the involved nodes, which is challenging in the sea environment as nodes are not stationary, but rather move due to tides and currents in the ocean. The problem of reliable delivery and void avoidance was addressed in [14], in which four schemes were proposed.