| As the population on earth continues to grow,the oceans have become an inevitable choice for human survival and development.Underwater Sensor Networks(UWSNs)have received great attention from scholars and governments due to the wide range of applications in marine environmental research and disaster monitoring,marine life exploration,marine resource exploration and development,military defense and security,and assisted navigation.Routing protocols play a crucial role in UWSNs,which determine the best transmission paths.Therefore,the study of routing protocols for UWSNs has important practical significance.However,the design of routing protocols for UWSNs also faces great challenges,such as,acoustic communication making UWSNs have longer delay,noise interference as well as multipath effect brings about a higher bit error rate.Moreover,UWSNs also have the characteristics of energy limitation,high topology dynamics,and low bandwidth.Facing the issues and challenges,in this thesis,a series of routing protocols for UWSNs are proposed by combining the techniques of meta-heuristic algorithms,grey prediction,and reinforcement learning considering energy balance,node mobility prediction,link quality and stability,and AUV-aided.Specifically,the main work of this thesis includes the following aspects.1.Considering energy balance and delay,a routing protocol based on the improved ant colony algorithm and Technique for Order Preference by Similarity to an Ideal Solution(TOPSIS)is proposed.The protocol improves the ant colony algorithm according to the characteristics of UWSNs and optimizes the ranking of the TOPSIS using the improved ant colony algorithm.Secondly,the protocol comprehensively evaluates factors such as hop distance,residual energy,node density,and pheromone concentration to prioritize the candidate nodes,and the candidate node with the best ranking result is selected as the next-hop.In addition,the protocol designs a state transition rule for nodes to avoid the overuse of some nodes in the network,so as to balance the energy consumption of the whole network and prolong the network lifetime.Finally,the performance of the protocol is evaluated and compared by simulation experiments.2.Considering the mobility as well as the energy limitation of nodes in UWSNs,a routing protocol based on node mobility prediction is proposed.The protocol provides a node mobility prediction rule based on the improved GM(1,1)model and further presents a method to predict node mobility behaviors.Besides,a forwarding cost is calculated for each candidate forwarding path based on residual energy and path distance,and then a path selection factor is calculated according to the forwarding cost and mobility prediction indicators of candidate nodes,and the candidate node with the smallest path selection factor is selected as the next-hop node.Simulation results show that the proposed protocol exhibits good adaptability to node mobility in UWSNs.3.For UWSNs,the state of the communication link is poor,which has a significant impact on the package delivery rate.Therefore,a routing protocol based on link state is investigated.Firstly two metrics,link quality and link stability,are defined to evaluate the link state.Further,a path evaluation formula is given to evaluate the advantages and disadvantages of all the candidate paths and select the next-hop node on the optimal path taking into account the residual energy and link state.Additionally,inspired by the Q-learning idea,a path maintenance algorithm is designed in the protocol based on the Q-value reward and punishment mechanism,which improves the delivery rate.Finally,the performance of the protocol is evaluated using the NS3 simulation platform.4.In recent years,the rapid development of Autonomous Underwater Vehicle(AUV)has effectively expanded the application of UWSNs,and AUVs become an important auxiliary tool in UWSNs.The thesis introduces AUVs into the design of routing protocol and proposes a reliable and energy-efficient routing protocol with AUV-aided.The protocol uses a hybrid mechanism of AUV-aided transmission and pure routing modes to improve the packet delivery rate.In the protocol,an abnormal node filter mechanism is designed based on the improved local outlier factor(LOF)algorithm,and an efficient AUV path planning algorithm and AUV-aided transmission scheduling rules based on an optimized genetic algorithm are presented.Furthermore,the performances of AUV-aided transmission as well as the optimized genetic algorithm are evaluated through simulation experiments and compared with some existing protocols.5.Field experiments are an important means to test the performance of the protocols for UWSNs.In the thesis,the real underwater testbed-Qinghai Lake watershed online monitoring experimental testbed is introduced,and the hardware equipment composition,the equipment performance parameters,and the software architecture used in the real testbed of each research phase are specified.Subsequently,the design scheme of the UWSNs field experiment topology was elaborated in detail.Finally,the test results of the field experiments are analyzed. |
