# An AUV-Aided Cross-Layer Mobile Data Gathering Protocol for Underwater Sensor Networks +
## 4 Description of Our Proposed Cross-Layer Mobile Data-Gathering Protocol
### AUV Discovery Phase
In this figure, CLMD with DL-MAC outperforms all other protocols by almost handling all data packets up until 100 nodes. When the node density further increases, the PDR of CLMD with DL-MAC slightly decreases by almost 1%. However, when the node density is up to 100 nodes, CLMD with ED-MAC delivers most of the packets (almost 98%), while it has a better delivery ratio than CLMD with UWAN-MAC protocol. When the node density is increased, the PDR of CLMD with ED-MAC decreases correspondingly to only deliver less than 78% in dense networks. This is mainly because of the spatial reuse property that is used in CLMD with ED-MAC is not as efficient as it is in CLMD with DL-MAC protocol. It is noteworthy that the PDR of CLMD with UWAN-MAC with only 50 nodes is able to handle 99% of the data packets. However, when the number of nodes is further increased, the PDR of CLMD with UWAN-MAC reduces significantly by delivering approximately 20% in a high density network (with 300 nodes). This is mainly because of the long propagation delays, which cannot prevent the spatial-temporal uncertainty problem, leading to increasing the number of collisions. As shown in Figure 8, the network goodput of all protocols is proportional to the nodes density. When the number of nodes is low (with 50 nodes), the network goodput increases correspondingly, except CLMD with UWAN-MAC, which reaches a saturation point within 150 nodes. Our proposed protocol, CLMD with DL-MAC, achieves a higher network goodput than that of CLMD with ED-MAC and CLMD with UWAN-MAC when their nodes density are the same. This is mainly because of that the higher the number of subframes in CLMD with DL-MAC, the more available slots can be settled

Figure 7: Packet delivery ratio vs. node density. as the nodes density increases. This means that CLMD with DL-MAC has the ability to handle more packets by having more slots to the sensors. On the other hand, the goodput of CLMD with ED-MAC is continuously increased while the density of the nodes increased too. However, it still reaches a lower value than that of our proposed protocol. This is due to the simplicity of CLMD with ED-MAC during all three operational phases than others. In Figure 9, we can observe that the higher the density of nodes, the higher the probability of collision which are presented to reserving the channel, except CLMD with DL-MAC protocol. Our proposed protocol (CLMD with DL-MAC) is more efficient than other protocols by having less percentage of packets lost when the density of nodes increases. This is due to the MAC protocol that is used in our proposed protocol, which is efficiently able to schedule the nodes by dividing the network area into a multi-layer to avoid any possible vertical collisions among the sensor nodes located in adjacent layers. Subsequently, each layer has \(k\) subframes to be settled by cluster heads located in the two-way distance from each other to avoid any potential horizontal conflict. By having a

Figure 8: Goodput vs. node density. Figure 9: Probability of collision vs. node density. higher \(k\) subframe configurations with a fixed traffic rate, our proposed protocol is efficiently able to handle more nodes. However, the CLMD with UWAN-MAC begins to lose a small number of packets when the number of nodes is 50. When the number of nodes increases, the percentage of packets lost of CLMD with UWAN-MAC is significantly increased by losing approximately 80% of the total packets when the number of nodes is 300. This is mainly because of its inefficient scheduling, which significantly leads to overhearing and more collisions. ## 6 Conclusions

This paper has presented a study of a cross-layer protocol with the aim of developing efficient and scalable protocol to enhance the performance of underwater sensor networks (UWSNs).