# 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
As UWSNs use acoustic waves, which are significantly different from terrestrial sensor networks that rely on radio waves to communicate with each other, designing a cross-layer protocol for underwater networks using acoustic communication is affected by many factors, such as high propagation delay, low bandwidth, and energy constraints. In this paper, a new cross-layer mobile data gathering scheme, CLMD, has been proposed to integrate the routing and MAC layer in UWSNs. In a distributed manner, CLMD selects a group of sensors as CHs and assigns a time slot to their members to facilitate their communication with cluster heads. The cluster heads have the responsibility to collect the information from sensors and deliver them to the AUV when it arrives. After clustering, the AUV travels the whole area to find the list of CHs and assigning a frame time to each cluster. If the the number of data packets is increased, CLMD still can keep its performance and the network lifetime high for a long time. CLMD can improve the scalability and resolve the void problem in sparse networks. We have evaluated the impact of routing layer on our propose cross-layer protocol. We then assessed the impact of MAC layer on the cross-layer protocol in order to select the best MAC protocol (CLMD with DL-MAC) for our proposed cross-layer protocol. Using an extensive simulation study, the performance of CLMD has been compared against those of other cross-layer protocols recently reported in the literature. Simulation results have shown that CLMD outperforms other protocols in terms of packet deliver ratio, energy consumption, and network lifetime with varying numbers of nodes. Meanwhile, the performance of the chosen MAC protocols (CLMD with DL-MAC) has also been compared against those of other MAC protocols. The simulation results indicated that CLMD with DL-MAC can obtain a better delivery ratio, energy saving, and the probability of collision. For the future work, we plan to enhance the performance of the cross-layer protocol by using an adaptive scheduling phase, which considers a changeable traffic rate during the operational phase. Another future interest lies in testing the reliability of real-life experiments. Although it is an expensive and complicated task to conduct a test bed in real experiments considering the different network sizes and scenarios involved, a real-life experiment with these ideas would better characterize the implementation outcomes of the different solutions proposed in this paper. It is also planned to investigate the low latency AUV-based data gathering schemes for time-critical applications in UWSNs. **Author Contributions:** : [PERSON], [PERSON], and [PERSON] developed the algorithm and analysed the results. [PERSON] carried out the computer simulations and wrote the manuscript. The simulation model was developed by [PERSON] and [PERSON], [PERSON] and [PERSON] assisted with the integrity of the research and also to revise the manuscript. All authors have read and agreed to the published version of the manuscript. **Funding:** This research received no external funding. **Acknowledgments:** This research was conducted at the first year of career as an Assistant Professor at Naif Arab University for Security Sciences. **Conflicts of Interest:** The authors declare no conflict of interest. ## References

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