Research And Analysis Of AIS Network Performance Based On OPNET

The AIS system is a part of the modern vessel traffic management system. The common standards were made and promoted by the International Maritime Organization (IMO), the International Telecommunications Union (ITU), International Association of Lighthouse Authorities (IALA) and other organizations in the1990s. Its working principle is to broadcast the dynamic information of the position, speed, course combined with the static information of the ship name, call sign, draft, cargo risk and etc. to the ships and the shore stations nearby through the very high frequency (VHF) channel, so that the ships and base stations could grasp the dynamic and static information of the nearby ships and coordinate immediately to take the necessary avoidance action, which plays a significant role in supporting of the safety of the vessel traffic.As Chinese maritime transportation becomes increasingly busy, the base stations might lose the position information of part of the ships due to channel congestion caused by the excessive vessels in the busy ports under the existing technology and equipment, as well as the standard and prescriptive AIS wireless communication methods, which results in the security risk. This paper studies the relationship between the AIS communication report rates and the shipboard base stations in the busy waters based on the self-organized time division multiple access protocol (SOTDMA) communication which is the core protocol of the AIS system, and the simulation tool-OPNET, in order to analyze the upper limit of report rates under a certain number of ships and the influence of the number of ships on the communication channel under a certain report rates.This paper first outlines the application status of the AIS communication network development, focuses on the introduction of the network communication theory based on the SOTDMA protocol. After a brief introduction about the simulation modeling mechanism of OPNET, this paper designs an AIS network communication model based on the OPNET simulation platform by the analysis of the AIS communication network architecture, and finally validates the rationality of the network topology of the simulation model.This paper stresses the SOTDMA protocol, designs the network model, the node model and the process model on the OPNET simulation platform according to SOTDMA protocol. Based on this platform, this paper builds ship models and base station models to set up a communication network model. In the simulation model, this paper focuses on the number of ship nodes, report rates, and other parameters to analyze the influence of network performance. Therefore, the report rates change dynamically according to the number of ship nodes, so as to avoid the network congestion.