## 2 Related Work and Our Contribution  
The authors in [16] propose a novel energy efficient protocol (NEFP) that selects forwarder nodes within a restricted zone from a source to a destination. Nodes that are close to the destination are given preference to take part in the routing process. The forwarding probability of a packet is also calculated along the expected routing path using Markov chains. The time for which a node holds a received packet is set so as to reduce interference. However, it requires the localization information of sensor nodes, which consumes surplus energy to locate the positions of nodes. Additionally, localization is difficult to achieve in underwater communications, as nodes change their positions frequently with water currents, and nodes within the restricted forwarding zone die early because of frequent selection as forwarders. In order to avoid interference and reduce void hole formation, a routing protocol is proposed in [17]. The protocol selects forwarder nodes on the basis of a cost function. The cost function is calculated for every node on the basis of its number of neighbors, the hop count and its distance form the sender. A sender node selects a forwarder node among its neighbors having the greatest value of the cost function. However, the protocol requires localization information of the sensor nodes. The energy hole repairing-depth-based routing (EHRDBR) [18] considers the death of low-depth nodes in the depth-based routing (DBR) protocol [19]. In DBR, the low-depth nodes die early because of frequent selection as forwarders. This creates energy holes in the network, which affects the delivery of the packets to the sink. EHRDBR detects an energy hole and replaces it with a live node. This avoids the loss of data packets. However, the detection of an energy hole and the moving of a live node to its exact position are cumbersome. These require localization information, which is challenging to acquire in underwater communications. The authors in [20] propose a routing protocol based on the Markov model to mitigate the channel noise and interference in underwater communications. The probability of a path is first found on the basis of its stability, its adaptation with respect to the changing traffic of data and the number of hops (less hops are preferred). The data is then routed along the best selected path. However, as a result of nodes' movements and the unreliability of the links in underwater channels, the properties of a selected path may change within the time of calculation of the path and its selection as a route. This, in consequence, results in the loss of the effectiveness of the selected path for data transmission. The opportunistic void avoidance routing (OVAR) protocol forwards packets from a source to a destination using opportunistic routing [21]. The relay nodes are selected on the basis of the successful delivery probability of a packet and packet advancement. However, the protocol involves the localization information of sensor nodes. It also suffers from the early death of nodes close to the water surface. A channel-aware routing protocol is proposed in [22] to avoid the zones in which forwarders are not available and in which the shadowing effect prevails (shadow zones). The protocol combines the history of nodes with successful packets' transmission, the number of hops and the power control to select the candidate forwarder nodes. The proposed protocol achieves high throughput and energy efficiency. However, its performance is compromised in dense networks in terms of high end-to-end delay. This is due to the constant checking of successful packets' transmission history. The hydrocast protocol proposed in [23] uses depth-based opportunistic routing along with a dead and recovery method.The protocol aims to mitigate the interference and energy consumption in the underwater data routing of nodes.