Partial Ambiguity Fixing for Ionospheric Delay Estimation

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Solution Overview

Problem

Current methods for determining phase components of carrier signals in satellite navigation systems face challenges such as maximizing the number of reliably fixable ambiguities, dealing with systematic errors, and efficiently resolving integer phase ambiguities, especially under severe multipath conditions and low elevation satellite geometries.

Innovation Solution

A method that selects a sequence for resolving phase ambiguities based on a predefined requirement for the probability of wrong resolution and an upper bound on measurement biases, using instrumental code and phase biases determined from reference stations, and employing a search tree to optimize the fixing sequence, while considering environmental biases and azimuthal separation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If sequential fixing (bootstrapping) is used to resolve integer phase ambiguities, then the reliability of the first fix is maximized, but the number of reliably fixable ambiguities is reduced

Engineering Contradiction:

Improvereliability of the first fixVSAvoidnumber of reliably fixable ambiguities

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent applies dynamic optimization by determining the fixing sequence adaptively based on current measurement quality, satellite geometry, and ionospheric conditions rather than using a static predetermined order. This allows the system to dynamically adjust which ambiguities to fix first, maximizing both reliability and the total number of fixable ambiguities under varying operational conditions

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the optimization criterion from maximizing first-fix reliability to maximizing the number of fixable ambiguities subject to a minimum reliability threshold. This parameter transformation allows the system to fix more ambiguities while maintaining acceptable reliability levels, directly resolving the contradiction between these two objectives

Inventive Principle:

Principle #35Parameter changes

2Measurement precision

If all integer phase ambiguities are resolved to achieve high positioning accuracy, then the positioning precision is improved, but the computational burden increases significantly

Engineering Contradiction:

Improvepositioning accuracyVSAvoidcomputational burden

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent implements partial ambiguity resolution by selecting and resolving only the most critical ambiguities that have the highest impact on positioning accuracy, rather than attempting to resolve all ambiguities. This partial action approach achieves sufficient positioning precision while significantly reducing the computational complexity of the integer least squares search

Inventive Principle:

Principle #16Partial or excessive action

Solution Approach 2:

The patent segments the ambiguity resolution process into two stages: first resolving a subset of critical ambiguities using optimized sequential fixing, then using these resolved ambiguities to constrain and simplify the resolution of remaining ambiguities. This segmentation reduces the overall computational burden while maintaining high positioning accuracy

Inventive Principle:

Principle #1Segmentation

3Measurement precision

If ionospheric delay is estimated from L1 and L2 code measurements, then the ionospheric error can be determined, but the code noise is increased due to BPSK modulation

Engineering Contradiction:

Improveionospheric delay estimation accuracyVSAvoidcode measurement quality

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent merges code measurements and carrier phase measurements into a combined estimation process for ionospheric delay. By combining these two measurement types with complementary characteristics, the system achieves more reliable ionospheric estimation than using code measurements alone, while the carrier phase measurements help mitigate the high noise level inherent in BPSK-modulated code measurements

Inventive Principle:

Principle #5Merging (Combining)

4Measurement precision

If carrier phase measurements are used for positioning, then the measurement accuracy is improved by three orders of magnitude, but the integer phase ambiguities must be resolved which increases system complexity

Engineering Contradiction:

Improvecarrier phase measurement accuracyVSAvoidambiguity resolution complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent performs preliminary action by resolving integer ambiguities for a selected subset of satellites first, using these resolved ambiguities to establish a reliable baseline for positioning. This preliminary ambiguity resolution simplifies subsequent processing and reduces the overall complexity compared to attempting to resolve all ambiguities simultaneously

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS8456355B2Partial ambiguity fixing for multi-frequency ionospheric delay estimation

Publication Date: 2013.06.04 DEUTSCHES ZENTRUM FÜR LUFT UND RAUMFAHRT E V

AI summary

A method is suggested for robust estimation of a subset of carrier phase integer ambiguities for precise ionospheric delay estimation. The advantages of this method are the precise estimation of receiver and satellite biases, an increase in the number of reliably fixable ambiguities, and an improved accuracy for the ionospheric delay estimation.