Research On MAC Protocols For Typical Scenarios In Underwater Acoustic Networks

The ocean is indispensable for the sustenance and advancement of humanity.The exploration,preservation,and responsible utilization of marine resources,along with the maintenance of the vitality of marine ecosystems,are paramount.Underwater acoustic networks play a pivotal and irreplaceable role,providing essential technical support for the development of marine resources,the protection of marine environments,and the progression of oceanographic research.Using underwater acoustic signals for communication,underwater acoustic networks allow different underwater equipment to connect with each other.However,the complicated nature of underwater channels,such as long propagation delay,narrow bandwidth,high error rate,high spatiotemporal dynamics,and half-duplex operation,poses significant challenges for designing MAC protocols.Despite these challenges,I have developed creative solutions that are specifically designed to meet the distinctive needs of underwater acoustic networks.In recent years,the MAC protocol for underwater acoustic networks has become a major focus of research.However,due to the intricate and dynamic nature of the marine environment,as well as the high cost and challenges of sea trials,there has been limited implementation of research on real hardware platforms and thorough evaluation in actual underwater environments.In the realm of underwater communications,this study adopts a practical application perspective to comprehensively examine the characteristics of underwater channels.The primary focus is the investigation of MAC protocols in three distinct scenarios: a smallscale network with a central node,large-area coverage with a complex hierarchical-structure distributed network,and remote bidirectional string networks.Furthermore,the research includes experimental verifications conducted in real marine environments.The principal research work and innovative achievements are synthesized as follows:(1)Time Sequence-based Dynamic on-Demand Assignment MAC Protocol: In order to address the networking needs of small-scale underwater nodes with a central underwater node,an underwater Wi Fi network architecture is utilized.This network includes a base station and multiple terminal nodes with varying characteristics,with the base station providing network access and interconnection services to the underwater terminal nodes.To cater to the diverse channel access requirements,mobility,and random access of the heterogeneous nodes,a time Sequence-based Dynamic on-Demand Assignment(SDDA)MAC protocol is proposed.The SDDA protocol integrates reservation and time scheduling to achieve on-demand scheduling of channel resources,while avoiding the complexity of time synchronization,reducing the number of control packets,preventing data conflicts,and minimizing energy consumption and latency.Additionally,the protocol leverages the long propagation delay characteristic of underwater acoustic communication to support parallel transmissions from different locations,thereby significantly improving channel utilization.Both simulation experiments and sea trials have confirmed the substantial advantages of the SDDA protocol in terms of channel utilization,end-to-end delay,and packet delivery ratio.(2)Hierarchical Cross-layer Optimized MAC Protocol Based on Time-Frequency Scheduling: In order to address the needs of complex,scalable distributed networking with large-area underwater coverage,a hierarchical underwater acoustic cellular network architecture has been implemented.This architecture consists of a two-tier structure,with the first tier including gateway nodes and multiple base stations,and the second tier comprising multiple clusters,each containing a base station node and various terminal nodes.To tackle the challenges related to channel access management in such a scalable hierarchical architecture,a new protocol called Hierarchical Cross-layer optimized MAC protocol based on Time-Frequency Scheduling(HC-TFS)has been proposed.HC-TFS is an innovative hierarchical cross-layer method that integrates frequency division,time scheduling,channel reservation,and cross-layer mechanisms to efficiently manage two-tier network data transmission.This protocol effectively resolves data conflicts within clusters,between clusters,and in the two-tier networks,while also appropriately allocating channel resources based on data volume requirements,leading to a significant improvement in channel utilization.Simulation experiments and sea trials have verified the superior performance of the HC-TFS protocol in terms of network throughput and channel utilization.(3)Robust and Adaptive Pipeline MAC Protocol: A multi-hop underwater acoustic string network architecture is utilized to facilitate underwater remote and bidirectional networking.These networks comprise a remote terminal,multiple relays,and a gateway.However,due to their reliance on a single path for data transmission,they often suffer from low end-to-end throughput,poor reliability,and challenges in fault detection and recovery.To address these issues,a Robust and Adaptive Pipeline MAC protocol(RAP)has been introduced.RAP focuses on enhancing network throughput through a schedule-based concurrency algorithm,real-time control of network slot planning for improved scalability,adaptive modulation and coding schemes based on channel quality for enhanced data transmission reliability,as well as a fault-adaptive detection network recovery algorithm to bolster fault tolerance.The RAP protocol’s environmental adaptability,fault detection and recovery capabilities,and efficient data transmission have been validated through simulation experiments and sea trials.