Research And Performance Simulation Of Multiple Access Method For VDE Shore-based System

VHF Data Exchange Terrestrial(VDE Terrestrial,VDE-TER)can achieve up to about 32 times the traditional ship automatic identification system(AIS)by introducing high-order modulation and demodulation technology,multi-carrier waveforms and expanding channel bandwidth.The transmission rate of the system can provide high-speed information transmission services for international busy ports.However,faced with the increasing demand of port user access network,the existing multiple access method of VDE-TER system is limited by the number of random access channel slots,and has the problems of high probability of multiuser access collision and high access delay.In view of the above problems,the main research contents of this paper are as follows:(1)In order to improve the access success rate of VDE-TER ship resource application messages,this thesis proposes a random access method based on clustering,and improves and innovates the number of ship clustering,cluster head selection algorithm,random access slot division,random access process based on clustering and power control method of non-cluster-head ships.In the proposed method,the random access channels of VDE-TER are further divided into intra-cluster access slots and cluster-head access slots.When a ship needs to send a resource application message,it first sends the resource application message to the cluster-head ship,and then the cluster-head ship adds all Maritime Mobile Service Identify(MMSI)of the ship that needs to apply for resources to the unified resource application message and sends it to the base station.Through two level access,the success rate of access is improved.The simulation results show that compared with the multiple access method of VDE subsystem defined in ITU-R M.2092 recommendation,the proposed random access method based on clustering can increase the access success rate of ship resource application messages by 40.63%on average and reduce the access delay by 26.98%on average.(2)In order to further verify the adaptability of the proposed method to the overall VDES system,a VDES multiple access simulation platform is developed based on OPNET simulation software,and the simulation function of multiple access protocol defined for different subsystems in ITU-R M.2092 recommendation and IALA G1139 standard is realized.Then,in accordance with ITU-R P.1546 document,the coverage of each subsystem of VDES is analyzed to determine the best simulation area.Finally,the main evaluation indicators of different multiple access protocols are simulated and analyzed based on the VDES multiple access simulation platform.The simulation results show that:in order to ensure the safe and stable operation of the AIS subsystem,the total number of AIS ships within the coverage of a single base station should be less than 100 ships,and the total number of reports should be less than 3000;In ASM subsystem,when the transmission demand of single data packet is greater than two time slots,compared with Random Access TDMA(RATDMA)and Increment TDMA(ITDMA)protocols,average performance of Multiple Increment TDMA(MITDMA)protocols is improved by 101.38%and 20.1%respectively;In the VDE-TER system,a single base station can accommodate about 200 data packets per frame on average,and the average access delay of the system is about 6s.In this paper,the research and optimization of random access method for VDE-TER system and the performance simulation analysis of multiple access protocol for different subsystems of VDES provide data reference for future construction and application of VDES.