GNSS Navigation Message Compact Ephemeris Acquisition
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Solution Overview
Problem
Current GNSS navigation messages do not efficiently reduce acquisition time for receivers without prior ephemeris and clock information, particularly in unassisted or partially assisted modes, leading to increased uncertainty in satellite positioning.
Innovation Solution
Incorporating a second, more compact set of ephemeris and clock data (DECH) into each subframe of the navigation message, with multiple copies distributed evenly, allowing for quicker satellite acquisition without additional assistance data, reducing the waiting time for precise data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a single set of DECH data is transmitted in each subframe, then the navigation message structure remains simple, but the cold acquisition time increases because the receiver must wait for the complete DECH set
Solution Approach 1:
The DECH data set is segmented into two distinct parts: a first DECH set containing full-precision ephemeris and clock correction data, and a second DECH set containing compact ephemeris data. This segmentation allows the receiver to acquire positioning information at different precision levels, reducing cold acquisition time while maintaining the ability to provide high-precision positioning when needed.
Solution Approach 2:
The patent transmits more DECH data than traditionally required by including the second compact DECH set in addition to the first full-precision DECH set. This excessive action ensures that the receiver can immediately calculate satellite positions using the compact data while waiting for the complete data set, thereby reducing acquisition time without sacrificing final positioning accuracy.
2Speed
If compact DECH data is transmitted, then acquisition speed improves, but positioning precision decreases
Solution Approach 1:
The system dynamically adapts the precision of satellite position calculation based on the available data. Initially, the receiver uses the compact second DECH set for rapid satellite acquisition with reduced precision. Once the complete first DECH set is received, the system transitions to high-precision positioning calculations, providing a dynamic precision level that matches the data availability.
Solution Approach 2:
The compact second DECH set is transmitted in advance within each subframe, enabling the receiver to perform preliminary satellite position calculations before the complete first DECH set is available. This preliminary action allows the receiver to display satellite positions and begin positioning operations immediately, with the understanding that precision will be improved once the full data set is received.
3Loss of time
If the second DECH set is transmitted only once per subframe, then data redundancy is minimized, but the maximum waiting time for DECH data approaches the full subframe duration
Solution Approach 1:
The patent applies different transmission strategies to different parts of the navigation message. The first DECH set is transmitted with standard frequency (once per subframe), while the second compact DECH set is transmitted with increased frequency (at least twice per subframe). This local quality differentiation ensures that the compact data, which enables rapid acquisition, is available more frequently without unnecessarily increasing the overall message size.
Data Source
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Figure 3
AI summary
A GNSS radio signal comprises a navigation message transmitted as a sequence of frames, each frame consisting of a plurality of subframes, each of which contains a first set of ephemeris and clock correction data (DECH) sufficient for calculating a satellite position and satellite clock error. Each subframe further contains a second set of DECH, more compact than the first set of DECH, but sufficient for calculating said satellite position and satellite clock error to a lesser degree of accuracy, at least two copies of the second set of DECH being contained in each subframe, such that the time difference between two consecutive copies does not exceed 70% of the duration of the subframe.