Terminal Positioning Technology For LEO Satellite Communication System Based On Time Of Arrival

At present,the Global Satellite Navigation System(GNSS)can provide relatively high positioning accuracy,but as an independent communication system,the LEO satellite communication system cannot completely rely on the GNSS system for normal operation.Instead,an independent terminal positioning solution is needed,which can provide an additional means of obtaining terminal position information in the event of GNSS failure or interference.The research goal of positioning problems is to improve positioning accuracy.The goal of this paper is to control positioning errors,meet positioning needs,and more accurately locate target terminals.This article focuses on the terminal positioning technology using Time of Arrival(TOA)as the positioning parameter,and conducts research from three aspects: ground terminal positioning system based on LEO satellite communication system,time parameter estimation method,and satellite selection strategy.The specific content is as follows:(1)Terminal positioning system.After a comprehensive analysis of the current research status and prospects of LEO positioning,taking into account the orbit characteristics of LEO satellites and the needs of mobility management,a positioning system based on TOA estimation was studied.On this basis,a ground terminal positioning method based on RTT measurement was proposed,and corresponding low orbit satellites were established in STK software to simulate and analyze the positioning performance of the system.The GDOP situation under different conditions was compared,providing a theoretical basis for the following research.(2)Method for estimating time parameters.For the TOA positioning system,the most important thing is to accurately estimate the signal TOA.This article takes the relatively mature "Starlink" satellite as an example to introduce the detailed structure and synchronization sequence of its downlink Ku band OFDM signal,and studies the frame synchronization algorithm based on the main synchronization sequence(PSS);For the RTT terminal positioning system,this article also provides a detailed analysis of the time parameter estimation algorithm based on OFDM signals.(3)GDOP analysis based on Starlink constellation.Compared to medium and high orbit constellations,low orbit constellations have a larger configuration.In order to achieve global coverage,the number of satellites can reach several thousand or even tens of thousands.During positioning,there are many visible satellites at the terminal,so it is necessary to choose a suitable satellite combination from them to meet the positioning requirements.This paper takes the "Starlink" low orbit satellite constellation as the research object,establishes a complete constellation model in STK,and analyzes the visibility of the ground terminal to its satellites above.On this basis,different satellite combinations were selected from the available satellites,and the advantages and disadvantages of their positioning accuracy were compared and analyzed.The principles that should be followed and the situations that should be avoided in selecting satellites were obtained,further improving the positioning accuracy.