Dual-Frequency GNSS Receiver Bias Removal
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Solution Overview
Problem
Existing global navigation satellite systems (GNSS) face limitations in achieving high accuracy due to ionosphere errors, particularly in single-frequency receivers, where ionosphere gradients and biases like inter-frequency and inter-signal group delays are not accurately accounted for, leading to positioning errors exceeding half a meter during normal operation and tens of meters during high solar activity.
Innovation Solution
A dual-frequency GPS receiver method that forms ionosphere-free code and carrier combinations, accounting for biases such as Tau-Group-Delay, inter-signal code bias, and user-SBAS biases, and uploads these biases into the receiver, while using a Kalman filter to estimate real-time troposphere perturbations, thereby eliminating the need for ionosphere corrections and improving navigation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If SBAS systems use first order ionosphere correction maps, then the system complexity is reduced, but positioning accuracy deteriorates with errors exceeding one half meter during normal operation and tens of meters during high solar activity
Solution Approach 1:
The patent transitions from first order ionosphere correction to second order ionosphere correction by changing the mathematical model parameters. This involves using more sophisticated correction formulas that account for higher order ionospheric effects, thereby improving positioning accuracy while maintaining manageable system complexity through systematic modeling approaches.
Solution Approach 2:
The patent introduces dual-frequency GPS receivers as an intermediary element to measure ionospheric delays directly. By using the L1 and L2 frequency signals from GPS satellites, the system can calculate ionospheric total electron content (TEC) and apply these measurements to correct single-frequency SBAS receiver positions, effectively mediating between the SBAS system and the ionosphere to improve accuracy.
2Object-affected harmful factors
If dual-frequency receivers form ionosphere-free combinations, then ionosphere-induced errors are eliminated, but the device complexity increases due to additional signal processing requirements
Solution Approach 1:
The patent extracts the ionospheric delay component from the GPS signals by forming ionosphere-free linear combinations of L1 and L2 measurements. This mathematical extraction eliminates the first-order ionospheric effect from the positioning calculations, removing the harmful factor while using well-established signal processing techniques.
Solution Approach 2:
The patent makes the dual-frequency receiver serve multiple functions: it not only provides its own high-accuracy positioning through ionosphere-free combinations but also generates ionospheric correction data that can be used to assist single-frequency SBAS receivers. This multi-functionality justifies the additional complexity by providing benefits to the broader SBAS ecosystem.
3Ease of operation
If SBAS systems are designed for single-frequency receivers, then the system is easier to operate, but the ability to correct ionosphere errors is limited
Solution Approach 1:
The patent segments the SBAS system into two functional components: dual-frequency reference receivers that measure ionospheric delays and generate correction data, and single-frequency user receivers that apply these corrections. This segmentation allows each component to be optimized independently - the reference receivers handle the complex ionosphere measurement while the user receivers maintain operational simplicity.
Solution Approach 2:
The patent implements a feedback mechanism where dual-frequency receivers continuously measure ionospheric conditions and provide real-time correction data back to the SBAS system, which then distributes these corrections to single-frequency receivers. This feedback loop ensures that ionosphere corrections are dynamically updated based on actual atmospheric conditions, improving reliability without complicating user receiver operation.
Data Source
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AI summary
A method for removing biases in dual frequency GNSS receivers circumvents the need for ionosphere corrections by using L2(P) in combination with either L1(P) or L1(C/A) to form ionosphere-free ranges. A table of biases is stored in microprocessor controller memory and utilized for computing a location using corrected ionosphere-free pseudo ranges, A system for removing biases in dual frequency GNSS receivers includes a dual frequency GNSS receiver and a controller microprocessor adapted to store a table of bias values for correcting pseudo ranges determined using L2(P) in combination with either L1(F) or L1(C/A ).