The Research And Realization Of AIS Time Slot Reuse Algorithm

With the development of AIS(Automatic Identification System),vessels equipped with AIS can communicate with vessels or base stations nearby thus improving the safety of navigation.But at the same time,the increasing of the number of vessels installed with AIS will led to the crowding of the data link,which threatens the stability of AIS communication and brings potential safety hazard to navigation.AIS slot reuse algorithm can effectively alleviate the link congestion resulted from high data link load and manage the communication slot selection conflict.Therefore when there is congestion on the data link,AIS slot reuse algorithm can still help the vessels smoothly communicate to ensure the safety of the vessel navigation.This paper gives the AIS slot reuse algorithm for different time slot selection algorithm and tests the reliability of AIS slot reuse algorithm in different stage.Firstly,the paper studies the RATDMA(Random Access TDMA),ITDMA(Incremental TDMA),SOTDMA(Self-organized Time Division Multiple Access),FATDMA(Fixed Access TDMA)time slot selection algorithm of AIS and realizes the RATDMA algorithm,SOTDMA algorithm and ITDMA algorithm by using C language.Then,the paper also researches the definition the classification and the usage of time slot reuse and analyzes the congestion problem of the link according to the International Standard ITU 1371 protocol in detail,gives the adjacent slot rule and the contrary channel rules and the reasons as well as redefines the specific time slot status and redefines the time slot reuse priority when the occupancy of time slot is in different level.In the process of studying the algorithm above,the paper designs and tests the alternative time slot,divides them into routine selection and slot reuse selection and gives the rule of choosing the alternative time slot.The paper simulates the operation process of AIS to verify the designed slot reuse algorithm.When testing the algorithm the design divides into three modules.Firstly the external time slot occupancy module simulates the generation of time slot status table of the vessel station.Secondly the time slot selection module controls the AIS system and selects the transmission time slot.Thirdly,the display module shows the states of the external occupancy slot,and the selection of the time slot occupancy states during the selection of the transmission slot,as well as the selection of the final transmission slot and other parameters.Finally,the paper realizes the design according to the test method given in the International Standard IEC61993-2,and analyzes test results.The whole process is implemented by using C language in the Windows platform Qt.