Research On VDES-based Ad Hoc Network Access Protocol For Vessels

With the expansion of international trade,the explosion of vessels and the message types challenges the traditional marine communication system.This thesis proposes the novel Media Access Control(MAC)protocols based on the original Self-organized Time Division Multiple Access(SOTDMA)protocol to ensure the reliability of the system.The designed protocols are suitable for the next-generation maritime communication system,i.e.,the Very High Frequency(VHF)Data Exchange System(VDES).The proposed MAC protocols can provide theoretical' reference and technical support for the development of MAC protocol standards in VDES.Firstly,this thesis summarizes the message types in different channels of VDES.Aiming at the problem that the time slot collision rate of the original SOTDMA protocol increases sharply with the increase of the number of messages,we use probability formulas to study the causes.Subsequently,to reduce the time slot collision of the channels in VDES,this thesis proposes a VDES based Self-organized Time Division Multiple Access(VSOTDMA)protocol.In the VSOTDMA protocol,a message type directional migration scheme is set to ensure high-priority message transmission reliability.This thesis establishes the VDES protocol simulation system and analyzes the relationship among the packet report rate,the number of vessels and the time slot collision rate.Besides,to overall reduce the time slot collision,this thesis proposes a novel MAC protocol for VDES,i.e.,the Feedback based Time Division Multiple Access(FBTDMA)protocol.By adding the collision feedback mechanism,the vessel can reduce the time slot collision gradually.The performance of the FBTDMA protocol is analyzed in terms of time slot collision rate,channel utilization rate and the successfully transmitted information in the VDES protocol simulation system.Finally,according to the actual situation of the vessel's motion state,the VDES protocol simulation system is used to simulate the time slot collision rate in the large scenario.This thesis also compares the application scope,advantages and disadvantages of the SOTDMA protocol,VSOTDMA protocol and FBTDMA protocol.