# Cross-Layer-Aided Opportunistic Routing for Sparse Underwater Wireless Sensor Networks
## 6 Performance Evaluation
### Simulation Results
#### 6.2.2 Comparison with Typical Protocols
EFlood outperforms the other three protocols at various traffic rates for different payload sizes, since each packet is forwarded directly without a handshake strategy in EFlood. At low traffic rates, the delay performance of CARP is better than FBR due to the effectiveness of the burst transmission strategy. CLOR has better transmission reliability than that of CARP due to the coding strategy in the burst transmission process. Thus, more packets in CLOR can be recovered than that in CARP. Less packets are required to be retransmitted in CLOR than that in CARP, since the packet may be sent by the sender with more times. Then, the average end-to-end delay of a packet in CLOR is smaller than that in CARP. When the payload size is small, the delay performance of CARP degrades heavily as the traffic rate increases, whereas the delay performance of CLOR is slightly increased at high traffic rates, because the transmission strategy is heavily influenced by the collision that is increased at higher traffic rates. In CLOR, the back-off strategy can handle the collision introduced by the negotiation. However, the time interval of a node in the BACKGROUND state increases significantly with large payload size. Thus, the delay performance of CLOR degrades sharply with large payload size compared with that with small payload size for different traffic rates. Nevertheless, CLOR still outperforms CARP at high traffic rates. Figure 14 shows the energy efficiency of the four routing protocols at different traffic rates \(\lambda_{T}\) and for different payload sizes. As expected, three handshake-based protocols show better energy efficiency than that of EFlood. The energy efficiency of the three handshake-based protocols is close, because the inherent characteristics of redundancy transmission in EFlood introduce more energy for delivering a packet. At high traffic rates, EFlood heavily suffers from the collision problem, and more energy is wasted in flooding, which results in the ineffectiveness of energy performance. Figure 15 shows the Goodput of the four routing protocols at different traffic rates \(\lambda_{T}\) and for different payload sizes. At low traffic rates, the Goodput of the four protocols are closed. As the traffic rate increases, CARP and CLOR perform approximately the same and outperform other two protocols. This is because the burst transmission strategy increases transmission effectiveness. We can find that the Goodput values of the three handshake-based protocols obviously outperform EFlood, because the collision heavily influences the transmission reliability of the protocols based on flooding. The probability of collision increases heavily as the payload size increases, which in turn significantly influences the transmission efficiency of EFlood. When the payload size is 512 B, the Goodput of CARP slightly decreases at high traffic rates, whereas the Goodput of the other three protocols still increases. This suggests that the probability of collision is large enough at high traffic  
rates and heavily influences the effectiveness of burst transmission in CARP. However, CLOR outperforms the other three protocols for different conditions as well.