GLONASS Ambiguity Resolution Through Calibration-Free IFB Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The presence of inter-frequency bias (IFB) in GLONASS satellite signals degrades the accuracy of integer ambiguity resolution in global navigation satellite system (GNSS) receivers, particularly in mixed receiver types and firmware versions, due to frequency division multiple access (FDMA) causing mis-alignment between phase and code observations.
Innovation Solution
A calibration-free method for GLONASS ambiguity resolution that allows ambiguities to naturally converge to integers by observing two GLONASS satellites with adjacent frequency numbers, combined with a least squares search process to estimate and correct inter-frequency bias (IFB) using carrier and code phase measurements, and a modified LAMBDA process to refine ambiguity resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If frequency division multiple access (FDMA) is used to transmit GLONASS signals on different frequencies, then satellite signal transmission capacity is improved, but inter-frequency bias degrades ambiguity resolution accuracy
Solution Approach 1:
The patent changes the parameter of frequency channel number to model and compensate for inter-frequency bias. By introducing a linear relationship between IFB and frequency channel number, the system can estimate and correct biases across different GLONASS frequencies, thereby maintaining measurement precision while preserving the FDMA transmission capacity.
Solution Approach 2:
The patent introduces an intermediary model that relates inter-frequency bias to frequency channel number. This intermediary relationship allows the system to estimate biases for satellites on different frequencies based on their channel numbers, effectively mediating the conflict between multi-frequency transmission and precise ambiguity resolution.
2Measurement precision
If receiver-dependent values are used to mitigate inter-frequency biases, then ambiguity resolution accuracy is improved, but firmware updates and system complexity increase
Solution Approach 1:
The patent enables the receiver to self-correct for inter-frequency biases by using the modeled relationship between IFB and frequency channel number. Instead of requiring external calibration data or firmware updates, the system autonomously estimates and compensates for biases based on observable parameters, thereby reducing device complexity and maintenance requirements.
Solution Approach 2:
The patent extracts the frequency channel number as a key parameter that can be used to model and remove inter-frequency biases. By separating the bias estimation into a distinct modeling step based on channel numbers, the system simplifies the overall processing while improving accuracy, avoiding the need for complex receiver-dependent calibration procedures.
3Measurement precision
If multiple GLONASS satellites with adjacent frequency numbers are observed simultaneously, then inter-frequency bias estimation accuracy is improved, but satellite visibility requirements increase
Solution Approach 1:
The patent performs preliminary action by using the frequency channel number to predict and model inter-frequency biases before they affect ambiguity resolution. By establishing the linear relationship between IFB and channel number in advance, the system can accurately estimate biases even with limited satellite visibility, reducing the strictness of satellite observation requirements.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Carrier phase measurements and code measurements are accessed (505) for satellite signals of a global navigation satellite system. An initial set of floating-point ambiguities are determined (510) based on the measurements, the initial set of floating-point ambiguities including inter-frequency bias (IFB). Disclosed example methods further include performing a least squares search process based on the initial set of floating-point ambiguities to determine a set of integer ambiguities and an estimate of the IFB (515). In some examples, an additional (e.g., wide-lane) filter is used to realize a combination of carrier phase and code IFB. In some examples, the resulting IFB estimate and the set of integer ambiguities are used to estimate a position of a receiver (520), determine a satellite correction signal, or otherwise.