# Cross-Layer Protocol Based on Directional Reception in Underwater Acoustic Wireless Sensor Networks
## 5 Simulation Results
### Performance Comparisons  
In this section, the performance of CLIC is compared with that of the RL-based QELAR [12], the geolocation-based VBF [13] with different pipelines of 600 m and cross-layer protocol CITP [20] with a focus on interference and collisions. Meanwhile, we analyze the influence of the weight values (\(\xi\) and \(\delta\)) on the performance of CLIC, as the priority of CT is influenced by the weights \(\xi\) and \(\delta\). All protocols are compared in the same three-dimensional space. Figure 8: Energy consumption of CLIC. Figure 7: PDR of CLIC. Figure 9 shows the relationship between the end-to-end delay of different protocols and the number of nodes. From Figure 9, it can be seen that the end-to-end delay of CLIC is not much higher than that of the VBF but much less than that of the QELAR, and it decreases as the number of nodes increases because the relay selection of the CLIC takes into account the important factors (end-to-end distance, node congestion, and interference) that affect the end-to-end delay as well as the reduced handshake MAC protocol that reduces end-to-end delay. Figure 10 demonstrates the packet delivery ratio of different protocols with different numbers of nodes. Due to the integrated routing-MAC, the CLIC obtains a higher PDR than those of the QELAR and VBF and is stable as the number of nodes increases. The MAC protocol of the CLIC reduces packet collisions by suppressing packet transmissions that may cause interference and uses a concise reservation channel mechanism to reduce the number of control packets in the network, thus improving network PDR. The number of data transmissions in a network has a significant impact on the energy efficiency of the network. For the same number of packets, the higher the number of transmissions, the less energy efficient the network is. As shown in Figure 11, the energy efficient CLIC is higher than that of the QELAR, CITP, and VBF because CLIC integrates  
Figure 10: Comparison of PDR versus the number of nodes. Figure 9: Comparison of end-to-end delay versus the number of nodes. routing-MAC, where the MAC protocol allows packets to be transmitted with minimal overhead, and the routing protocol limits the number of hops to be delivered, thus reducing the number of transmissions. The energy efficiency of CLIC with \(\xi=0.8\) is higher than that of \(\xi=0.2\). A low-interference route reduces packet collisions and thus reduces the number of packet transmissions, improving energy efficiency. Figures 12-14 show a comparison of the performance of protocols at different packet generation rates. Figure 12 shows the relationship between the end-to-end delay and packet generation rate of the protocols. The end-to-end delay of CLIC with \(\xi=0.2\) is not much higher than that of the VBF, but much less than that of QELAR and CITP. This is because nodes with a high level of congestion have a higher CT priority and can send packets first, thus reducing network congestion and reducing end-to-end delay. Figure 13 compares the PDR of the protocols under different packet generation rates. The PDR of CLIC and CITP decreases as the packet generation rate increases but is still greater than VBF and QELAR. The increase in packet generation rate leads to an increase in packet collisions. The CITP with \(\xi=0.8\) cross-layer takes into account the local interference situation in the network and prevents nodes from transmitting in advance to areas of high interference, thus reducing packet collisions and increasing PDR. Figure 11: Comparison of energy consumption versus the number of nodes. Figure 12: Comparison of end\(-\)to\(-\)end delay versus packet generation rate. Figure 14 shows the relationship between the energy efficiency and packet generation rate of the protocols. As the packet generation rate increases, there are more packets in the network, leading to an increase in packet collisions. Failed packet transmissions result in more packet transmissions, which lead to a reduction in energy efficiency.