Design and derivation of the dual transponder carrier ranging system

The accuracy of microwave ranging is mainly limited by the frequency instability of the oscillator that generates the carrier phase signal. A dual transponder carrier ranging method is used to minimize the oscillator noise by combining the reference and the to-and-fro measurements. This ranging approach together with pseudo-noise ranging or other means can be used to measure the inter-satellite distance with a high precision. The pseudo-noise ranging system or other ranging systems help to solve the integer circles while the dual transponder ranging system guarantees the accurate fractional circle. The two satellites work in the master-slave mode. The range measurements are derived on the master satellite while the slave satellite just coherently transfers the received signal, so that the dual transponder ranging system does not need to rely on the time tagging system to synchronize the two satellites. This study first describes the dual transponder carrier ranging system and shows how the system removes most of the oscillator noise components effectively. Then, a detailed design scheme on the frequency planning of the ranging system is presented and the supporting analysis illustrates the feasibility of this system. Based on the design innovation, a laboratory demonstration system is assembled to verify the realizability of the dual transponder ranging system. The experimental results demonstrate that a high level of accuracy (about 30 μm under laboratory circumstance) can be achieved by the use of the proposed dual transponder carrier ranging system.

Simulation of dual transponder carrier ranging measurements

The most dominant error source for microwave ranging is the frequency instability of the oscillator that generates the carrier phase signal. The oscillator noise is very difficult to filter due to its extremely low frequency. A dual transponder carrier ranging method can effectively minimize the oscillator noise by combing the reference phase and the to-and-fro measurement phase from the same single oscillator. This method does not require an accurate time tagging system, since it extracts phases on the same satellite. This paper analyzes the dual transponder carrier ranging system by simulation of the phase measurements with comprehensive error models. Both frequency domain and time domain noise transfer characteristics were simulated to compare them with dual one-way ranging. The simulation results in the two domains conformed to each other and demonstrated that a high level of accuracy can also be achieved by use of the dual transponder carder ranging system, with relatively simple instruments.

Dual transponder ranging performance in the presence of oscillator phase noise

A dual transponder carrier ranging method can be used to measure inter-satellite distance with high precision by combining the reference and the to-and-fro measurements. Based on the differential techniques, the oscillator phase noise, which is the main error source for microwave ranging systems, can be significantly attenuated. Further, since the range measurements are derived on the same satellite, the dual transponder ranging system does not need a time tagging system to synchronize the two satellites. In view of the lack of oscillator noise analysis on the dual transponder ranging model, a comprehensive analysis of oscillator noise effects on ranging accuracy is provided. First, the dual transponder ranging system is described with emphasis on the detailed analysis of oscillator noise on measurement precision. Then, a high-fidelity numerical simulation approach based on the power spectrum density of an actual ultra-stable oscillator is carried out in both frequency domain and time domain to support the presented theoretical analysis. The simulation results under different conditions are consistent with the proposed concepts, which makes the results reliable. Besides, the results demonstrate that a high level of accuracy can be achieved by using this oscillator noise cancelation-oriented ranging method.

An alternative integer recovery clock method for precise point positioning with ambiguity resolution

When using Global Navigation Satellite System(GNSS)measurements,Precise Point Positioning with Ambiguity Resolution(PPP-AR)has been a popular substitute for relative positioning in geoscience applications.Compared with the Fractional Cycle Biases(FCB)method,the processing of Integer Recovery Clocks(IRC)products estimate,especially for ambiguity datum fixing,is so complex that its application has been greatly limited.Based on the concept of“carrier range”,we introduce an efficient way to implement the IRC method,termed as the alternative IRC method in this paper.In this method,the fixed ambiguities derived from PPP-AR using the FCB method,and not a fixed-ambiguity datum,are fixed in the IRC products estimate.This greatly reduces the complexity of implementing the IRC method and does not influence the accuracy of positioning.The alternative IRC method outperforms the FCB method by corroborating the consistency of daily positions in nature with international GNSS service weekly solution.To confirm this improvement,global positioning system measurements acquired over a year(2016)from approximately 500 globally distributed stations were processed.The accuracy of IRC products is approximately 20 ps and is highly stable for this year.Moreover,comparing the positioning accuracy of the FCB method to the alternative IRC method,we find that the mean root mean square over the year falls evidently from 2.03 to 1.65 mm at the east component.Therefore,we suggest that the alternative IRC method should be implemented when estimate IRC products.