Time-Differenced Carrier Phase Observables for Positioning
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Solution Overview
Problem
Current navigation satellite systems face limitations in positioning accuracy due to distortion of signals through the atmosphere and the integer ambiguity problem in carrier phase measurements, which affects the precision of position estimation.
Innovation Solution
The method involves computing time-differenced carrier phase observables and adjusting the anchor epoch update interval to maintain continuity and minimize error accumulation, allowing for more accurate and precise position estimation by forming delta-carrier-phase observables.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If carrier phase measurements are used for position estimation, then position precision is improved (down to centimetre-level or millimetre-level), but the integer ambiguity problem arises making the carrier phases ambiguous by an unknown number of cycles
Solution Approach 1:
The patent segments the carrier phase measurement process into two distinct parts: (1) code-based pseudorange measurements that provide unambiguous but less precise range information, and (2) carrier phase measurements that provide precise but ambiguous range information. By processing these segmented measurements separately and then combining them through a mathematical relationship, the system achieves both precision and unambiguity in the final position estimate.
Solution Approach 2:
The patent transforms the ambiguous carrier phase parameter into a useful measurement by changing its mathematical form. Specifically, it uses the relationship between code phase and carrier phase to derive a corrected carrier phase measurement that removes the integer ambiguity while preserving the high precision. This parameter transformation allows the system to convert an ambiguous high-precision measurement into an unambiguous high-precision measurement.
2Reliability
If code-based positioning is used, then the integer ambiguity problem is avoided, but positioning accuracy is limited (approximately 15 meters) due to code distortion through the atmosphere
Solution Approach 1:
The patent merges two different measurement types with complementary characteristics: code-based pseudorange measurements (unambiguous but less precise) and carrier phase measurements (precise but ambiguous). By combining these measurements through a mathematical relationship that eliminates the ambiguity term, the system produces a final position estimate that achieves both unambiguity and high precision, overcoming the limitations of using either measurement type alone.
Solution Approach 2:
The patent introduces an intermediary mathematical relationship between code phase and carrier phase measurements. This intermediary relationship serves as a bridge that allows the system to transfer the unambiguous information from code measurements to the carrier phase measurements, thereby converting the ambiguous carrier phase into a precise and unambiguous measurement without directly observing the ambiguous parameter.
3Device complexity
If anchor epoch update interval is increased, then computation complexity is reduced, but error accumulation increases affecting solution accuracy
Solution Approach 1:
The patent implements a dynamic anchor epoch update strategy where the update interval is not fixed but adaptively adjusted based on the current state of the measurement system. When measurement conditions are favorable and error accumulation is low, the system increases the anchor epoch interval to reduce computation. When error accumulation approaches acceptable thresholds or measurement quality degrades, the system decreases the interval to maintain accuracy. This dynamic adjustment optimizes the trade-off between computational efficiency and solution accuracy.
Solution Approach 2:
The patent incorporates feedback mechanisms that continuously monitor the quality of carrier phase measurements and the level of error accumulation. This feedback information is used to adjust the anchor epoch update interval in real-time, ensuring that the system maintains optimal performance. The feedback loop allows the system to respond to changing measurement conditions and maintain high accuracy while avoiding unnecessary computations when conditions are favorable.
Data Source
AI summary
Some embodiments of the invention relate to methods carried out by a navigation satellite system (NSS) receiver for estimating parameters useful to determine a position. The NSS receiver observes NSS signals from a plurality of NSS satellites. The method comprises performing a delta-carrier-phase-observables-computation procedure. It is further determined whether a criterion, indicative of (i) continuity of carrier phase measurements from an anchor epoch to a terminus epoch, and/or (ii) stability of NSS satellite measurement geometry from the anchor epoch to the terminus epoch, is satisfied, and, if not, the anchor epoch is moved forward. Then, after determining whether the criterion is satisfied and after either moving the anchor epoch or not, the delta-carrier-phase-observables-computation procedure is performed again for a new terminus epoch. Systems and vehicles using such a method are also disclosed.