Research Of Uplink Synchronization Method On Low Orbit Satellite

The oceans,deserts,mountains,and the north and south poles,which account for most of the earth's surface,are basically not covered by terrestrial cellular networks.In order to meet people's increasing communications needs,low-orbit satellite communication systems can realize any time anywhere in the world.Fill the blank space.Low-orbit satellites and the ground are in relatively high-speed motion.The coverage and inter-satellite distances exhibit fast time-varying characteristics as the satellites move at high speeds.This poses a great challenge to network synchronization in low-orbit satellite communication systems.In the case of time division multiple access,in order to avoid overlap of the signals in adjacent time slots allocated to different users,the uplink needs to be synchronized.This paper first describes the research status of synchronization in low-orbit satellite communication systems,explains the main research contents and research background of this paper,introduces the principle of network synchronization,and the principle of synchronization based on satellites and ground in time division multiplexing access.Secondly,according to the six parameters of satellite orbits,the functional relationship between the spatial position of low-orbit satellites and time is deduced in the geocentric equatorial Cartesian coordinate system,and the low-orbit satellite constellation configuration is designed to provide research background on uplink synchronization in the context of low-orbit satellites.Then,the LEO satellite coverage was studied with a minimum elevation angle of 5 degrees.From the point of view of time,the satellite coverage on the ground is constantly changing.From a spatial point of view,satellite coverage density increases as latitude increases.Simulation results show that the low-orbit satellite constellation can achieve real-time global coverage when the minimum elevation angle is 5 degrees.Finally,in order to set the problem that traditional distance-based information is used to set the uplink synchronization that requires frequent updating of distance information and has low precision,an uplink synchronization method based on location information is proposed.By measuring the pseudoranges and forming the nonlinear equations,the user's position information and the inter-satellite clock error are calculated using the solution method based on the least squares principle.On the basis of obtaining position information and clock error,the user side combines the ephemeris information(satellite position,speed,number,etc.)in the satellite broadcast frame to calculate the relationship between the distance between the satellites and the space,and the distance converted into the propagation time.Get the user's uplink signal transmission timing advance.Adjusting the transmitter of the UE according to the transmission timing advance enables the uplink signal to arrive at the satellite with high accuracy just in the allocated time slot,so as to achieve the purpose of uplink synchronization of the low orbit satellite system.In the case of a minimum elevation angle of 5 degrees,STK and Matlab are used to simulate the uplink synchronization.Simulation results show that the proposed method can achieve uplink synchronization in low-orbit satellite communication systems with high accuracy,avoiding frequent ranging updates and higher accuracy.