# Void Avoidance Opportunistic Routing Protocol for Underwater Wireless Sensor Networks
## 4 Simulation Results
### Scenario 2:
#### 4.2.2 Results and Analysis
We also conclude from Figure 11 that for EEDOR and EEDOR-VA, the total number of transmitting nodes is relatively constant with the network density, especially with high transmission power levels, while it increases greatly with network density for DBR. Figure 11 shows that the number of nodes that actually transmit the data packets using EEDOR-VA is less than the number of transmitting nodes when using EEDOR. These results motivated us to study the extra energy consumed by EEDOR-VA during both hop count discovery and data transmission. Figure 12 illustrates the total energy consumption for the hop count discovery and data transmission processes. As shown in Figure 12a, in the network topology with 100 nodes, the energy consumed in data transmission is a little more than that consumed in hop count discovery. This similarity in energy consumption happens because the HCREQ and HCREP do not broadcast through the whole network and their size is much smaller than the data packets. Relative energy consumption is reversed when the density of the nodes increases, which increases the number of the nodes that can communicate with each other. This increase in node connectivity means more nodes will rebroadcast HCREQs and HCREPs to cover all connected nodes, while the data packets will be transmitted hop-by-hop through only the relay nodes with discovered hop count to deliver them to the destination. The same explanation is also true when using higher transmitting power levels, as shown in Figure 12b,c. Thus, the EEDOR-VA hop count discovery process is responsible for most of the total energy consumption of the network. Figure 12: EEDOR-VA total energy consumption per task at different transmission power levels. **Packet Delivery Ratio (PDR):** In this network topology, a lower value of packet delivery ratio of routing protocols is expected since the nodes are deployed far apart from each other, which makes void areas in the network more likely. Moreover, since the sensor nodes may be out of the communication range of each other, the forwarding sets may contain a small number of candidates or they will be empty and therefore will affect the PDR. We assess the performance of the comparison protocols by decreasing the void nodes in the network through increasing the number of deployed nodes and/or increasing the transmission power level. We simulate the three protocols at three transmitting power levels. Simulation results are shown in Figure 13. First, Figure 13a shows that using the smallest power level and the smallest number of nodes in our experiment, EEDOR-VA outperforms DBR and EEDOR. Increasing the number of nodes at the same power level for EEDOR-VA in Figure 13a or raising the power level with a different number of nodes for the three comparison protocols will help to increase the PDR to the maximum, as shown in Figure 13b,c. This occurs because an increase in the number of nodes or an increase in the power level leads to an increase in the number of next-hop forwarding candidates, and this helps to increase the probability of delivering the packet successfully. It is important to mention that, referring to [19], the power control method used by PCR protocol helps to increase the connectivity between the nodes. This increases the number of forwarding candidates. In DBR, the depth threshold mechanism and the large number of disconnected nodes tend to decrease the number of forwarding candidates. This decrease in forwarding candidates explains why, in [19], DBR outperformed the PCR protocol in energy consumption. It also explains the low PDR for DBR compared with the high PDR obtained by the PCR protocol. On the other hand, when we compare DBR with EEDOR-VA, the redundant packets and retransmissions in DBR are the reason for the extra amount of depleted energy. Additionally, the collisions in the DBR protocol are caused  
Figure 13: EEDOR-VA Packet Delivery Ratio (PDR) at different transmission powers. mainly by redundant packets, which increases the probability of packets being lost and decreases the PDR.