# An Energy-Efficient and Obstacle-Avoiding Routing Protocol for Underwater Acoustic Sensor Networks
## 5 Performance Evaluation
### Evaluation with Different Parameters  
Packet delivery ratio (PDR) is one of the fundamental performance measures of every routing protocol. The formula for calculating PDR is given as:  
\[PDR=\frac{N(R_{D})}{N(G_{S})}, \tag{11}\]  
where \(N(R_{D})\) is the number of distinctive packets received successful by the destination node, and \(N(G_{S})\) is defined as the total number of distinctive packets generated from the current node. PDR in the network refers to the ratio between the packets received by the destination node and the packets sent by the source node. We simulate the relationship of packet delivery ratio and the number of nodes of three routing protocols. In this simulation, the simulation duration is 500 s and the number of nodes varies between 50 and 500 with a step of 50. As shown in Figure 7, when the number of sensor nodes increases, the packet delivery ratio continues to increase. When the number of sensor nodes is only 50, PDR of the three protocols are relatively low. Since the number of sensor nodes is very small, it is impossible to form an optimal route. This may lead to packet loss during transmission, resulting in a low packet delivery ratio. Till the number of sensor nodes increases to 300, the packet delivery ratio continues to increase as the number of sensor nodes increases. This is because as the number of nodes increases, the number of neighbor nodes in the candidate forwarding relay set increases and the success ratio of transmitting the data packet from the current node to the destination node becomes higher. Therefore, adding sensor nodes will have a greater impact on network routing reachability. When the number of nodes is 300, the PDR of HHVBF and VHGOR protocols has increased by 35.9% and 17.6%, respectively. However, when the number of nodes reaches a certain value, PDR grows slower and is closer to the ideal value of 1. In this simulation, 300 can be seen as a turning point of the parameter--the number of nodes. When the number of nodes is 500, the PDR of HHVBF and VHGOR protocols has increased by 28.4% and 11.8%, respectively. Compared with HHVBF and VHGOR, EOAR always has the highest PDR with the same number of nodes. Therefore, it is observed from the evaluation that our proposed EOAR protocol can improve the packet delivery ratio compared with the other two protocols. \begin{table}
\begin{tabular}{c c} \hline \hline
**Name** & **Values** \\ \hline Simulation scene range & 9 km \(\times\) 9 km \(\times\) 7 km \\ Number of nodes & \(\leq\)500 \\ Bit rate & 9 kb/s \\ Data packet size & 200 B \\ Transmission range & 1.5 km \\ Transmission power & 10 W \\ Receiving power & 3 W \\ Idle power & 30 mW \\ Initial energy of every sensor node & \(10^{4}\) J \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Simulation parameters. The end-to-end delay is expressed as the total time that a packet is sent from the source node to the destination node. The end-to-end delay primarily includes several aspects of propagation delay, transmission delay, waiting time and calculation time. The number of nodes is the same as the simulation above varies from 50 to 500 with a step of 50. The simulation duration is 500 s.  
As shown in Figure 8, the end-to-end delays of the three different underwater acoustic network routing protocols are constantly changing. Compared to the HHVBF and VHGOR protocols, EOAR significantly reduces end-to-end delay. Till the number of nodes is up to 300, the end-to-end delay of the three protocols increases as the number of nodes increases. After that, the end-to-end delay of EOAR is significantly smaller than the other two protocols. The end-to-end delay of EOAR is 38.2%, 25.0% lower than that of HHVBF and VHGOR when the number of nodes is 300, respectively. This is because in spare network, there are a smaller number of potential forwarding relays. On the other hand, in a dense network, a node can find more potential forwarding relays, which takes more calculation time and waiting time than in a spare network.