| The construction and development of ISL is one of the development directions of future GNSS.The use of inter-satellite links for on-board data transmission and inter-satellite measurement can not only improve the navigation accuracy of the system,but also improve the system's autonomous navigation capabilities.China's BDS is faced with the difficult problem of global deployment.Therefore,it is of great strategic importance to vigorously develop the ISL.Under this background,this paper based on the BDS,from the requirements of inter-satellite ranging and the requirements of overseas satellites and domestic satellite communications,a preliminary study of ISL allocation in BDS is conducted.The details are as follows:(1)The working principle of ISLs and the link working system.Firstly,The specific functions and working principles of ISL are analyzed.Secondly,The working frequency band selection and working system are analyzed separately.And the ISL working system used in this paper is determined.(2)Determine the ISL allocation constraints and performance indicators.Firstly,the constellation configuration used in this paper is BDS(24 MEO satellites +3 IGSO satellites +3 GEO satellites),followed by analysis of the constraints between inter-satellite distance,inter-satellite antenna visibility,and inter-satellite geometry visibility,and mathematical descriptions and simulations are given.Finally,performance evaluation standards for inter-satellite communication and ranging are given.(3)Construction of an ISL allocation model.According to the ISL constraint conditions,using the mature ISL system of GPS and directed graph theory,an ISL allocation model is established.Finally,the simulation of the variation of main characteristics such as the inter-satellite pitch angle,inter-satellite distance,and azimuth angle is performed.(4)According to the link allocation model and constraint conditions,a link allocation method based on genetic algorithm for least delay data transmission is proposed,and simulation tests and results analysis are performed.The validity of the algorithm is analyzed from the perspective of data transmission scheme and the whole table transmission delay,and the performance of the algorithm is evaluated.The analysis of the simulation results shows that under the conditions of two domestic ground stations,inter-satellite data transmission is started at any time,and up to two timeslots(within 6 s)complete the task of returning data of all foreign stars.Meet the requirements for quick return of overseas data.(5)Based on the minimum data transmission link allocation method for delay,a link allocation method that takes into account inter-satellite measurement and communication is proposed,and simulation tests and results analysis are performed.The algorithm is simulated from the perspective of inter-satellite data transmission delay and inter-satellite PDOP values,and the effectiveness of the algorithm is verified.Through simulation and result analysis,the link allocation method proposed in this paper that takes into account the inter-satellite measurement and communication,in the case of only one ground station in China,the time delay of returning data from all foreign stars does not exceed 4 timeslots,and the inter-satellite PDOP value is only 0.3 greater than the minimum value.Meet the needs of inter-satellite data transmission and inter-satellite measurement. |
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