Research On Routing Protocol Of Underwater Acoustic Sensor Networks For Marine Water Quality Monitoring

Underwater Acoustic Sensor Networks(UASNs)are an important means for marine water quality monitoring.UASNs use underwater acoustic communication technology to connect underwater sensor nodes,integrating data collection and information transmission functions.With their advantages of self-organization,dynamic topology,scalability,and long-term deployment,UASNs can meet the mid-to long-term mission requirements of the covered area.The special characteristics of the underwater acoustic channel make hydroacoustic communication characterised by high time delay,high bit error rate and high energy consumption.UASNs routing protocols overcome the problems of low transmission rate,low reliability and energy constraints in UASNs by formulating packet forwarding policies,and can meet the quality of service requirements of different application scenarios,thus becoming a research hotspot in marine networking technology.This thesis focuses on the local water quality monitoring scenarios,and designs an efficient UASNs routing protocol based on the specific service quality requirements of different aquatic environments.Through the analysis of key issues such as the network lifetime,end-to-end delay,and reliability of UASNs,this thesis proposes a routing protocol that can meet the service quality needs of different application scenarios.The main research contents of this paper are as follows:First,facing the need for low energy consumption and long network lifetime for longterm ocean information monitoring application scenarios,this thesis proposes an adaptive clustering routing protocol for UASNs based on reinforcement learning.The protocol models the network as a multi-agent system,and allows the nodes to select the global optimal route collaboratively through reinforcement learning.To reduce the probability of hotspots generation,an adaptive cluster head selection algorithm that does not incur any additional communication overhead and does not require consensus from surrounding nodes is proposed,which enables nodes to autonomously decide whether they can act as cluster heads using routing and environment information.Additionally,a biased reward function is designed to feedback the effect of the adaptive cluster head selection algorithm on the routing performance and to encourage the nodes to select the cluster heads as relays.Simulation results show that the proposed adaptive clustering routing protocol achieves higher routing efficiency,lower energy consumption,and longer network lifetime than existing approaches.Second,facing the application scenario of maritime emergency communication which covers both delay-sensitive and delay-insensitive traffic,this thesis proposes a multi-objective routing protocol for UASNs.The protocol designs two relay selection algorithms for different types of traffic.For delay-sensitive traffic,we analyse the factors affecting end-to-end delay in UASNs and discusses the impact of link congestion,transmission hops and MAC protocols on delay.The delay-constrained energy-minimal routing is interpreted as a 0-1 integer linear programming,and the node that obtains the minimum link cost is selected as the best relay node by the Larac algorithm.For delayinsensitive traffic,routing protocols need to transmit data with low energy consumption and high reliability.The relay selection algorithm for delay-insensitive traffic allows each node to select the best relay by minimising energy consumption in a distributed manner,introducing the link quality parameter,enabling the routing protocol to identify paths with high throughput in multi-hop wireless networks.Finally,to address the problem of channel access difficulties caused by dense node deployment,a cross-layer protocol with low interference and congestion(CLIC)based on the spatial reuse characteristics of vector hydrophone directional reception is proposed.This protocol analyzes the network interruption probability under directional reception and performs cross-layer design by combining the routing protocol and medium access control protocol to adaptively form a route that bypasses nodes with high collision probability and congestion level.Based on the characteristics of spatial and temporal uncertainty of UASNs and the fact that data packet collision probability is high,a relay selection scheme based on neighbor interference and congestion level is proposed.This scheme balances the key factors that affect network performance to obtain high network throughput and low latency routing at a lower cost.Additionally,the protocol proposes a medium access control protocol with a channel reservation mechanism,which uses vector hydrophone directional beams to establish data transmission links with minimum interference and maximum capacity.Simulation results show that CLIC has higher network delivery rate,higher energy efficiency,and lower end-to-end delay.