Improvement And Simulation On Channel Access Protocol Of Shipborne AIS

Shipborne Automatic Identification System(AIS)realizes the channel access and the communication by Self-organized Time Division Multiple Access(SOTDMA)protocol.With the development of the economy,water traffic is more and more heavy,so slot collision of AIS exists in the waters with large traffic density.It cause the fail transmission of the information,appears for the monitored target does not update the information for a long time.After the update of the information,there is jumping phenomenon of location.It poses a risk to navigation safety and maritime regulation.So it is extremely necessary to study the channel access protocol of the AIS and reduce the slot collision rate to the standard development and pratical application of AIS.The main works are as follows:Based on the study of the principle of AIS,this thesis has achieved the simulation system of AIS channel access protocol to study the slot collision rate of the SOTDMA protocol.In the last,an improved slot reservation algorithm is proposed to reduce the slot collision rate.The main works are as follows:(1)This thesis makes a deep analysis on the principle of AIS,focused on the key technology of link layer and the work process of AIS.Then this thesis improves the slot collision rate probability model combined with the work process of AIS.(2)The SOTDMA protocol is simulated by C++ on the Visual Studio,which can achieve the goal of simulate the process of communication and autonomous self-organization slot reservation among the vessels at the same sea area.Then different number of users and the packet report rate are set,to study the slot collision rate performance of AIS.At the same time,the simulation results are compared with the theoretical analysis and the statistical analysis,verify the correctness of the simulation system.(3)The simulation results obtained in different scenarios are compared with the theoretical values.The analysis shows that the slot collision rate is close and the trend is consistent.Then the real AIS data time slot collision rate statistics,and simulation experiments in the real scene of the water area.By comparison,it is found that the difference of the time collision rate is within the acceptable range,and the reliability of the simulation system is verified.(4)An improved slot reservation algorithm is proposed in the situation that the slot collision rate of ships in the ship-intensive area is relatively high.It can be seen that the improved slot reservation algorithm has a lower slot collision rate when the load is same from the simulation results.