PPP-RTK Time Transfer for Long-Baseline Clock Bias Resolution
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Solution Overview
Problem
Existing time transfer methods struggle to achieve high-precision, real-time time transfer over long baselines due to dependence on external satellite products, atmospheric delays, and increased data transmission pressure, especially for RTK methods, while PPP methods are limited to post-processing and require high-precision satellite data.
Innovation Solution
A long-baseline real-time time transfer method based on undifferenced and uncombined PPP-RTK, utilizing a network of GNSS reference stations and a data processing center to generate satellite-related products internally, resolving receiver clock biases independently, and transferring these products to user stations for combined clock bias calculation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RTK method is used for time transfer, then real-time performance and short-baseline precision are improved, but it cannot eliminate atmospheric delays through differencing for long baselines and requires transfer of original observations increasing data transmission pressure
Solution Approach 1:
The patent segments the time transfer problem by introducing intermediate reference stations to divide long baselines into shorter segments. Each segment can be processed using RTK-like differencing techniques, while the overall long-baseline time transfer is achieved by combining results from multiple segments. This allows atmospheric delay elimination to be effective in each short segment while covering long baseline distances.
Solution Approach 2:
The patent uses reference stations as intermediary points between the transmitting and receiving ends. These reference stations provide common-view satellite observations that serve as mediators for eliminating atmospheric delays. By observing the same satellites from multiple reference station locations, the system can model and remove atmospheric effects that would otherwise limit long-baseline performance.
2Adaptability or versatility
If PPP method is used for long-baseline time transfer, then baseline length limitation is removed, but it depends heavily on external real-time precise satellite clock and orbit products
Solution Approach 1:
The patent implements self-service by enabling the receiver to generate its own satellite clock and orbit products through observations from multiple reference stations. Instead of relying on external products, the system uses the network of reference stations to locally estimate and provide the correction products needed for precise time transfer, making the system self-sufficient and more reliable.
Solution Approach 2:
The patent makes the reference station network serve multiple functions: it provides both the infrastructure for atmospheric delay modeling and the source of satellite product generation. The same reference stations that enable short-baseline RTK performance also generate the correction products needed for long-baseline operations, eliminating the need for separate external product sources.
3Speed
If RTK method transfers original observations to users, then real-time processing is enabled, but data transmission pressure and vulnerability to data loss increase
Solution Approach 1:
The patent extracts and removes redundant information from the data transmission process. Instead of transferring all original observations, the system extracts only the essential correction products (satellite clock and orbit parameters) that are needed for time transfer. This reduces the data volume significantly while maintaining the capability for real-time processing at the user end.
4Measurement precision
If PPP method uses batch least-squares adjustment, then high precision can be achieved, but real-time performance cannot be provided
Solution Approach 1:
The patent transitions from static batch processing to dynamic real-time processing. The system uses incremental algorithms that update time transfer solutions continuously as new observations arrive, rather than waiting for complete data sets. This dynamic approach maintains high precision by continuously refining estimates while providing real-time performance through incremental updates.
Data Source
AI summary
A time transfer method based on undifferenced and uncombined PPP-RTK is applied to a time transfer system including a PPP-RTK network end observation station network and PPP-RTK user end observation stations. The network end observation station network includes GNSS reference stations and a network data processing center. The user end observation stations include a time reference station and an ordinary user station. The method includes: acquiring GNSS observations collected by the GNSS reference stations and performing an undifferenced and uncombined PPP-RTK resolution to generate network end products; each of the user end observation stations performing an undifferenced and uncombined PPP-RTK resolution by using collected GNSS observations and the network end product to generate multi-GNSS receiver clock biases; and solving a combined inter-station clock bias by using the receiver clock biases of the ordinary user end observation stations and those of the time reference station serving also as user end.