Study On The Multi-channel MAC Protocol Of Maritime Broadband Wireless Ad Hoc Network

The rapid development of wireless communication technology allows mobile users to access various data services anytime and anywhere on the land.Due to the particularity of maritime geographic features,providing reliable data communication for maritime users is a challenging problem.Traditional maritime communication systems,such as the global maritime distress and safety system and the ship automatic identification system,mainly use HF and VHF for communication,which have low transmission rate,poor communication quality and limited coverage.Given the growing demand for maritime digital services,we need to develop maritime communications that support high-speed data rates and extend communication coverage.Based on the study of the structure of maritime broadband wireless communication network,this paper constructs a maritime broadband wireless ad hoc network.In view of the increase in the number of ships at sea and the increase of communication traffic between ships,this paper proposes the application of multi-channel technology in wireless ad hoc networks.Broadband wireless communication to the sea,and a distributed time-division-based multi-channel assignment MAC protocol(DTMAC)based on time division multiple access is designed for the network.The main research work of this thesis is as follows:(1)The thesis summarizes the research status of maritime wireless broadband networks at home and abroad,summarizes the characteristics of maritime wireless broadband technology,and summarizes the performance of existing maritime communication systems.Then the research status of multi-channel MAC protocol in wireless ad hoc networks is introduced,which lays a foundation for designing multi-channel MAC protocol for maritime broadband wireless ad hoc networks.(2)The SOTDMA protocol of AIS system is studied.The slot selection algorithm of SOTDMA protocol and the slot reservation collision rate are discussed.The theoretical analysis model of slot reservation collision rate is studied.The SOTDMA protocol of AIS system is simulated by network simulation software NS2.The self-organizing reservation of transmission time slot and the self-organizing communication between ships are realized.The simulation results of slot reservation conflict rate and theoretical analysis results are carried out.Analysis and comparison,the impact of the message reporting rate and the number of ships in the network on the slot reservation conflict rate.(3)A multi-channel MAC protocol(DTMAC)for maritime broadband wireless ad hoc network is proposed.The protocol divides the available bandwidth resources into one control channel and multiple data channels.The control channel is used to transmit ship safety related information.Emergency help information and negotiation information for multi-channel allocation,and transmission of Internet service information on the data channel.The TDMA channel access mechanism is used on the control channel to allocate a fixed time slot for each ship in the network.A mathematical model based on Markov chain is established for the time slot assignment protocol on the control channel.The relationship between the number of ships that successfully obtain the transmission time slot and the total number of time slots in one frame and the number of ships in the network is analyzed.Then the DTMAC protocol is simulated in NS2.Then compare the network performance of the DTMAC protocol and the SOTDMA protocol when transmitting security information.Finally,the network performance of multiple data channel allocation mechanisms of DTMAC protocol is evaluated.The simulation results show that the throughput of the network during maritime communication is greatly improved.