# Path Diversity Improved Opportunistic Routing for Underwater Sensor Networks
## 4 Simulation Result
In PICS, the forwarding depth threshold can also avoid partially invalid forwarding and ensure the packets can be forwarded to a neighbor with a lower depth than the average depth of the current candidate set. Because of the two-way message interaction, the delay of PRCS is greater than PICS. We plot the average energy consumption of the five protocols in Figure 6c. Energy consumption includes two parts in the simulations, packets transmission and neighbor information exchanging. PRCS only needs one-hop neighbor information supported by the beacon period, while two-hop neighbor information is exchanged in PICS, EPA and OVAR. Although all routing decisions in DBR are made locally, DBR results in higher average energy consumption due to multi-path forwarding and packet collision. The higher PDR and effective retransmission suppression make PICS and PRCS have a lower average energy consumption than others. We compare the PRCS protocol performances with different forwarding threshold in Figure 7. With the decrease of forwarding threshold \(P_{T}\), the average candidate number increases, as shown in Figure 7d. It makes the PDR of PRCS protocol increase, as shown in Figure 7a. In addition, it causes the end-to-end delay to increase and the average energy consumption to decrease. **C. Compared with the previous solutions in mobile scenario**: All nodes move except for the source and sink node and follow the model in [11]. We also measured the performance of PDR, average energy consumption and end to end delay, as shown in Figure 8. The minimum speed is 0 m/s and  
Figure 7: PRCS with different forwarding progress threshold. (**a**) Packet delivery ratio; (**b**) End-to-End delay; (**c**) Energy consumption per node and packet; (**d**) Average candidate number. the maximum speed is 1 m/s. In the simulation, we set the depth threshold parameter as \(D_{r}=20\) m in PICS, the holding time parameter meets \(\alpha<0.02\) in EPA, the forwarding threshold is \(P_{T}=10\) in PRCS, and the neighbor information update period is \(T=150\) s. To reduce the effect of nodes moving on the accurate neighbor information, we set a dynamic slot length that is related to half of the maximum propagation delay of node communication range multiply by a random value in the beacon process. In Figure 8a, the PDR performances of the five protocols in the mobile scenario are plotted. The PDR performance of DBR does not vary much with node moving, since all routing decisions in DBR are made locally based on a node's depth information. No topology or route information needs to be exchanged between neighboring nodes. It makes DBR have a better PDR performance, especially in the sparse network (e.g., nodes number less than 200). The PDR of OVAR, EPA, PICS and PRCS protocol decline significantly in mobile scenarios caused by the outdated neighbor information and routing information. As shown in Figure 8d, the candidate number of PICS declines seriously, but PRCS could provide enough candidate nodes with the appropriate forwarding threshold. Compared with EPA and OVAR, the larger candidate set size employed by PRCS and PICS will bring more candidate nodes involved in forwarding, which is conducive to node movement. In addition, the PDR performance of OVAR is lower than others, mainly because the available routing information is more likely to fail over time when there are fewer candidate nodes. As shown in Figure 8b, in PICS, the movement of nodes will decrease the number of candidate nodes, resulting in a smaller holding time at each hop. Thus, the end-to-end delay of PICS declines relative to the static scenario. Because of the neighbor information updating, the average energy  
Figure 8: Compared with the previous solutions in mobile scenario. (**a**) Packet delivery ratio; (**b**) End-to-End delay; (**c**) Energy consumption per node and packet; (**d**) Average candidate number. consumption of OVAR, EPA, PICS and PRCS increases, as shown in Figure 8c, especially in OVAR and EPA that require two-hop neighbor information.