## 2 Related Work  
This section discusses related algorithms for UWSNs. A cooperative algorithm is proposed in [19]. The network is divided into four regions. The list is prepared for all neighbor nodes in descending order and the protocol sorts and selects the destinations (DSNs) on the parameter values: higher residual energy and lowest depth. The source node forwards the information bag in the direction of the destination and forwarder node present in the same region. The protocol has a good lifetime of the network and maximizes the packet acceptance ratio. However, due to cooperation in the data packets forwarding, it maximizes the delay of the network. The nodes near to the sink die quickly because of high data traffic. The authors propose three energy efficient protocols in [20]. In the first protocol, the DSNs are chosen on the lowest depth and residual energy. The network lifetime increases in this protocol. In the second protocol, the DSNs are chosen on the fewest hops and lowest depth. This protocol decreases the path loss effects in data packet transmission. In the third protocol, the destination nodes are chosen on depth, residual energy, and the fewest hops. It improves the battery lifetime and packets delivery ratio. However, the destination node selection criteria increases the delay. The lowest depth nodes are mostly used and thus die quickly. In [21], the source nodes need information about depth and residual energy of relays for data transmission. The optimal forwarder is chosen from the set of forwarder nodes through the fuzzy logic mechanism. The relay nodes having the maximum PDR are chosen to transmit the information packets in the direction of destination nodes. The forwarder node waits for the defined interval of time before forwarding the data bags. The protocol has good results in energy and delay as well as because of cooperation high PDR is achieved. On the other hand, there is no checking mechanism either the data packets received are correct or erroneous. In [22], two partner forwarder nodes and the destination node transmit the information packets. The selection criteria of the destination and forwarder nodes are classified in two ways. The nodes are chosen on depth, residual energy and quality of the channel as well as on the signal-to-noise ratio (SNR). This algorithm improves the packet acceptance ratio. On the other hand, the protocol is not good in terms of delay. In [23], a proposed protocol considers the three parameters residual energy, depth and the link quality for choosing destination nodes. The link quality of the source nodes with the destination and forwarder nodes is considered. Depth threshold \((D_{th})\) is defined and varied according to alive nodes. Within the \((D_{th})\), the relay nodes are selected while the destination nodes are chosen its outside. If source nodes have no neighbor nodes in their range of \((D_{th})\), then the information packets are transmitted towards the destination nodes directly. If the source nodes have no neighbor nodes outside the \((D_{th})\), then the forwarder nodes are chosen as the destination nodes. If source nodes have no neighbor nodes inside and outside the \((D_{th})\), then data packets are dropped. Due to cooperation, the destination nodes receive two copies of information packets which are then combined by MRC technique. The protocol has good throughput. On the other hand, the protocol has maximum energy usage. Region-based cooperative protocol is presented in [16], in which the choice of destination and forwarder nodes depends on three parameters: depth, residual energy and SNR. To determine the location of the nodes, instead of GPS, the protocol uses received signal strength indicator (RSSI) with More-track technique. Based on the above mechanism, neighbor nodes are identified and selected. Four mobile final destination nodes are selected to receive the information bags from sensor nodesin half-duplex mode. Cooperation is performed when the destination nodes receive the data packets with BER value greater than 0.5.