# Cross-Layer-Aided Opportunistic Routing for Sparse Underwater Wireless Sensor Networks
## 6 Performance Evaluation
### Simulation Results
#### 6.2.2 Comparison with Typical Protocols  
Then, we simulate the four protocols for different traffic rates and for different payload sizes with \(\lambda_{T}=2.0\) packet/min, SL = 158 dB re uPa @ 1m source, \(N_{mBT}\)= 1, and \(N_{MBT}\) = 8. The comparison of CLOR against other typical protocols is shown in Figures 12-15. Figure 11: Network performances versus \(N_{mBT}\) for different payload sizes with a fixed \(N_{mBT}\): (**a**) PDR; (**b**) Average end-to-end delay; (**c**) Goodput. Figure 10: Network performances versus \(N_{MBT}\) for different payload sizes with a fixed \(N_{MBT}\): (**a**) PDR; (**b**) Average end-to-end delay; (**c**) Goodput. Figure 12 shows the PDR of the four routing protocols for different traffic rates \(\lambda_{T}\) and for different payload sizes. The PDR of CLOR is significantly better than that of EFload and FBR protocols, and it is better than CARP at high traffic rates when the payload size is large. At low traffic rates, Elfood shows the worst performance among the four protocols. All three handshake-based protocols outperform EFload, and the difference of PDR of these three protocols are small. In EFload, a node directly forwards a packet without handshaking with the surround nodes. However, this routing method cannot avoid the collision. In contrast, another three protocols use the handshake method to avoid the collision. The PDR for the four protocols decreases as the traffic rate increases, especially when the payload is large, because the collision and the interference significantly increase as the traffic rate increases. In addition, the probability of the collision exponential increases as the payload size linearly increases, and this is especially obvious when the traffic rate is high. EFload still suffers from the collision problem as the traffic rate increases. FBR can avoid collision at lower traffic rates. When the traffic rate increases, the probability of the successful ratio for the handshake that is triggered by a node decreases, and this will  
Figure 14: Energy efficiency: (**a**) Payload size = 128 B; (**b**) Payload size = 256 B; (**c**) Payload size = 512 B.  
Figure 13: Average end-to-end delay: (**a**) Payload size = 128 B; (**b**) Payload size = 256 B; (**c**) Payload size = 512 B.  
lead to the node dropping more packets than that at low traffic rates. In contrast, the burst transmission strategy used in CARP and CLOR can improve channel utilization and then decrease the probability of the collision in a network. Moreover, the transmission reliability can be further improved by the adaptive transmission strategy used in CLOR. At high traffic rates, the PDR of other three protocols decreases while CLOR still outperforms the other three protocols. The PDR of CARP decreases more sharply than the other three protocols for a large payload size, because the handshake strategy can effectively decrease the probability of the collision at small or middle traffic rates. At high traffic rates, the burst size significantly increases, and the transmission time is long for a large payload size. This leads to large transmission delay in one transmission. Then, the probability of the successful ratio of the handshake decreases, and more packets are dropped because of handshake failure. In CLOR, the back-off strategy used in the negotiation phase can effectively avoid the collision that is introduced by the handshake, and thus, CLOR is slightly influenced by high traffic rates for different payload sizes. Moreover, the congestion that is considered in the candidate set selection can further decrease the probability of the collision. In addition, the use of coding strategy in burst transmission can help to resist the influence of the bad channel condition since more multi-hop interference is introduced at high traffic rates. Figure 13 shows the average end-to-end delay of the four routing protocols at different traffic rates \(\lambda_{T}\) and for different payload sizes.