Reseach On Satellite Constellation Designing And Key Communication Technologies Of VDES

Since the beginning of the 21 st century,the mature and sound automatic identification system(AIS)has played a vital role in ensuring maritime navigation safety and reliable communication between ships.However,with the dramatically increase in the number of ships at sea in recent years,the amount of data exchanged between ships showed explosive growth,and the loss of data in the transmission process has occurred frequently in important shipping areas.The traditional AIS system has been unable to meet the various types of emerging ship applications in the communication,positioning,navigation and other aspects of service quality requirements.In 2013,the concept of VDES(VHF Data Exchange System)was first proposed by International Association of Lighthouse Authorities,and after several international conferences to discuss,VDES has been upgraded and follow-up evolution as AIS.This thesis focuses on the VDES satellite subsystem,studies the VDES satellite constellation design method to cover the earth's fixed area,and the performance optimization method of VDES communication link between the satellite and the ship based on cognitive radio technology.In particular,the research content of this thesis includes two parts: The first part,VDES satellite constellation design method based on genetic algorithm is researched.The thesis aims at designing the VDES satellite constellation to cover the Earth's fixed area.Based on the traditional genetic algorithm and satellite constellation design theory,analyzed and deduced the constraints of the common ground trajectory constellation,and then the common ground trajectory constellation is designed based on MATLAB and STK.The second part,the performance optimization method of VDES communication link between the satellite and the ship based on cognitive radio technology is studied.The thesis introduces the cognitive radio technology to enhance the communication link performance between the satellite and the ship in the VDES system.At the same time,the energy-based dual-threshold spectrum sensing technology is improved,and the link performance improvement of the traditional algorithm and the improved algorithm in the typical VDES star-ship communication scene is verified and compared by simulation experiment.The main contributions of this thesis are as follows: On the one hand,the design method of VDES satellite constellation based on genetic algorithm is proposed to optimize the performance of continuous seamless coverage of ground designated area.On the other hand,based on cognitive radio technology and its spectrum detection improvement technology to optimize VDES star-ship communication link performance,to improve the VHF frequency band utilization rate.The thesis studies show that,firstly,the ground trajectory constellation containing four medium orbit earth satellites designed by the VDES satellite constellation design method based on genetic algorithm,is compared with the polar orbit constellation containing six medium orbit earth satellites and the Walker-delta constellation containing ten medium orbit earth satellites,it's satellites are few and the cost is low.Although these three constellations are able to provide continuous uninterrupted communication services to the South China Sea.Secondly,the improved energy-based dual-threshold spectrum detection technology proposed in this thesis,can effectively improve the performance of VDES star-ship communication link is compared with the original spectrum detection technologies,which can alleviate the problem of spectrum resource tension in VDES star-ship communication.