| Satellite positioning is one of the main application means of satellite communication system.It has the advantages of all-weather,high precision and automatic measurement.It has been widely used in our daily life and social development.The use of satellites to search and rescue targets on land or at sea is an important development direction of positioning technology.At this stage,the development of search and rescue positioning systems is not very mature.The most widely used is the global satellite search and rescue system(COSPAS/SARSAT).In this paper,based on the signal system of COSPAS/SARSAT,the Galileo satellite navigation system with search and rescue payload is selected for the space segment satellites.When the ground monitoring station has only a single antenna,the time-sharing single-satellite time difference positioning technology is used to realize the target signal source.positioning,and finally complete the design and implementation of the search and rescue signal satellite positioning software,the specific content is as follows:(1)Time-division single-satellite time difference positioning technology.At present,the main positioning technology used in the Galileo search and rescue system is time-frequency difference joint positioning or tri-satellite time difference positioning.The ground gateway station needs to be equipped with more than two receiving stations with one antenna each,and the distress signal sent by the target source that can be transponded by multiple satellites which can oversee the target source at the same time.When the gateway receiving station has only one antenna or the target radiation source is shaded in zones with high angle of elevation only,so that cannot be accessed by multiple satellites at the same time,multi-satellite positioning conditions may not apply In order to solve the above problems,this paper studies the time-division single-satellite time-difference positioning technology on the basis of tri-satellite time-difference positioning,and elaborates the basic principle of timedivision and single-satellite time-difference positioning,and then the solution method of the positioning equation,which is a theoretical basis of the positioning software.(2)Real-time ephemeris prediction based on navigation message parsing.In order to obtain the instantaneous position coordinates of the satellites required for positioning,it is necessary to extract the original navigation messages of the satellites.This positioning system uses the U-Blox module to receive the original navigation messages of the Galileo satellites.Then the method of calculating the satellite position coordinates in the message is presented,and finally the satellite simulation scene by the ephemeris parameters is established in the software STK.The results show that the difference between the simulation data and the actual calculation results is very small,which meets the needs of the positioning system.(3)Design and implementation of satellite positioning software for search and rescue signals.The design and implementation of the positioning software is the focus of this paper.The positioning software is divided into six modules: the navigation message receiving module,the navigation message parsing module,the interaction module with the antenna tracking software,the interaction module with the signal detection software,the positioning module and the display module.This thesis first introduces the overall design process of the positioning software,then introduces the design ideas and methods of each module,and tests the functions of each module.After ensuring that the functions of the positioning software can run correctly,the positioning software,the antenna tracking software and the signal detection software are finally jointly debugged and tested.The test results show that the positioning system can successfully meet the requirements set by the project. |
