# DOW-PR DOlphin and Whale Pods Routing Protocol for Underwater Wireless Sensor Networks (UWSNs)
## 6 Performance Comparison and Analysis
### Simulation Results in the Dolphin Pods Routing Scenario  
In this section, the simulations are performed upon the dolphin pod routing in which all the sinks are placed on the water surface without any sink embedded \(D_{SM}\) underwater. It can be seen from Figure 12 that the similar trend of increasing PDR for DBR, WDFAD-DBR and DOW-PR protocol when network density increases. The reason behind the common trend is the fact that, if density of the network increases, there will be more probability of occurrence of active node(s) at the next hop and therefore a reduction of void holes. DOW-PR outperformed in terms of PDR in comparison to WDFAD-DBR and DBR. In DBR, the node having the lowest depth among the potential forwarding nodes will be selected as a next forwarder and will not consider the depth of the expecting hop, which results in increasing the chance of a void hole. However, WDFAD-DBR selects the next expecting hop on the basis of weighting sum of depth difference of the two hops, which reduces the chance of a void hole happening. The PDR of DBR and WDFAD is almost the same from node numbers 270-500, i.e., in a dense network. The reason is the presence of enough PFNs in the range of a source node, which reduces the probability of void hole. PDR of a dolphin pod is higher than WDFAD-DBR, primarily because WDFAD-DBR selects the next expecting hop on the basis of weighting sum of depth difference between the two hops. Nonetheless, a dolphin pod considers all the factors including weighting sum of depth difference of the two hops, the number of PFNs, suppressed nodes number, and the hop count value to sink. The difference between the PDR of dolphin pod and WDFAD is higher for a sparse network and reduces due to the dense network. Secondly, WDFAD-DBR drops the packet in the absence of PFN, but dolphin pod select a node for forwarding from the suppressed nodes and therefore prevent the loss of the data. The PDR of dolphin pod is higher than WDFAD-DBR in both sparse and dense networks. However, in a sparse network, WDFAD-DBR more often drops the packet due to high probability of void holes and therefore a more proportional gain of PDR in dolphin pods resulted. On the other hand, as node number increases and void hole probability decreases, the fraction gap in PDR results. Moreover, there are two types of void holes occurring in routing protocols. One is due to lack of a potential forwarder in the range of a source node and the other is due to the lack of energy in a potential forwarding node [34]. This means that there is a forwarding node of the source node but it doesn't have a sufficient threshold energy. The dolphin pod is trying to avoid both the void and energy holes. When the void holes occurred due to no PFN in the range of the source node, it selects a forwarding node from the suppressed nodes as shown in Figure 6. Subsequently, it reduces the re-transmissions and reduces the energy consumption due to redundant packets' avoidance. When the energy consumption is reduced, then the energy tax or an average energy expenditure per packet of each node is decreased as it is clear from Equation (22). Consequently, energy is conserved and therefore the occurrence of energy holes is also reduced. As a result, by overcoming both the void and energy hole, the PDR of the dolphin pods' routing scheme increases. The PDR statistics are shown in Table 5, in which we can easily notice the PDR improvement by 11.89%, 6.085% and 3.365% in the scenario where node densities are 200, 300 and 400, respectively. Moreover, dolphin pod routing assigns weight both to the packet advancement as well as to the network traffic density in such a way that priority is given to the less dense traffic path at the cost of packet advancement. The fitness function (HH) value will be less for the more dense path in which the probability of traffic density is high.