Research on inter-satellite measurement technique in high dynamic environment

An improved measurement algorithm, based upon the theory of two-way time transfer （ TWTT）, is proposed to measure satellites with high speeds. The algorithm makes theoretical analyses and corresponding deductions on a relative motion model of two satellites, and eliminates the measurement error caused by the equipment delay when a satellite moves at a high speed. Theoretical analysis and simulation results demonstrate that in comparison with the conventional TWTT algorithm, the proposed algorithm can significantly enhance the measurement accuracy of the inter-satellite ranging and time synchronization, and the algorithm is more effective with the relative velocity between the satellites and transmitting delay becoming larger.

Time synchronization and ranging under unknown positions and velocities

The process to achieve time synchronization and ranging for a network of mobile nodes is raising a concern among researchers, and hence a variety of joint time synchronization and ranging algorithms have been proposed in recent years. However, few of them handle the case of all-node motion under unknown positions and velocities. This study addresses the problem of determining ranging and time synchronization for a group of nodes moving within a local area. First, we examined several models of clock discrepancy and synchronous two-way ranging. Based upon these models, we present a solution for time synchronization with known positions and velocities. Next, we propose a functional model that jointly estimates the clock skew, clock offset, and time of flight in the absence of a priori knowledge for a pair of mobile nodes. Then, we extend this model to a network-wide time synchronization scheme by way of a global least square estimator. We also discuss the advantages and disadvantages of our model compared to the existing algorithms, and we provide some applicable scenarios as well. Finally, we show that the simulation results verify the validity of our analysis.

On new measurement and communication techniques of GNSS inter-satellite links

This paper studies the key techniques of the measurement and communication system for inter-satellite links(ISLs) of global navigation satellite system.A fixed link topology is designed based on the analysis of inter-satellite geometric properties and spatial parameters of the standard Walker24/3/2 constellation.This design can achieve full network coverage with small num-ber of hops,significantly reduce the number of ISLs,and enhance the feasibility and reliability of the system.A new time-division duplex mode,as well as an integrated measurement and communication scheme,is proposed based on the de-signed topology.Furthermore,mathematical formulas,error models,and modification methods regarding two-way ranging and time synchronization algorithms using spread spectrum non-coherent data frame for this new system are comprehensively dis-cussed.Theoretical analysis and simulation studies demonstrate that our design,compared with current GPS systems,has higher ranging and time synchronization precision,improved measurement efficiency,and higher channel utilization ratio and data transmission rate.It has no restrictions of constellation configuration,making it suitable for both MEO and the future MEO/GEO hybrid constellations.The results in this paper can serve as strong technical support for the next generation of GNSS ISL.