GNSS Velocity Protection Levels for Reliable Course Over Ground
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Solution Overview
Problem
Existing navigation systems, such as automated driving systems and advanced driver assistance systems, require reliability on the order of 99% or greater for velocity and course over ground calculations, which traditional methods using standard deviation cannot provide.
Innovation Solution
A GNSS receiver calculates protection levels for velocity and course over ground by utilizing phase range rate measurements and variance measurements, employing a weight matrix, shaping matrix, and least squares method to determine reliability, and transforms these into north, east, and up protection levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard deviation is used to estimate velocity accuracy, then the calculation is simple, but the reliability is only 68% which is insufficient for safety-critical systems
Solution Approach 1:
The patent changes the parameter from standard deviation (68% reliability) to protection level calculated using chi-squared distribution with 99.999% reliability. This involves transforming the accuracy estimation parameter from a simple statistical measure to a rigorous integrity parameter that accounts for worst-case scenarios including potential satellite signal failures
Solution Approach 2:
The patent performs preliminary calculations of the G matrix (geometry matrix) and its inverse, and pre-computes the protection level bounds before final velocity determination. This allows the system to quickly assess whether the current satellite geometry provides sufficient reliability without performing complete real-time calculations
2Reliability
If protection levels are calculated using chi-squared distribution with 99.999% reliability, then the reliability meets safety-critical system requirements, but the calculation complexity increases significantly
Solution Approach 1:
The patent segments the protection level calculation into distinct modular components: (1) G matrix computation from satellite positions, (2) inverse G matrix calculation, (3) protection level bound computation using chi-squared distribution, and (4) final velocity determination. This segmentation allows each component to be optimized independently and facilitates real-time implementation
Solution Approach 2:
The patent replaces traditional mechanical filtering approaches with a mathematical-statistical approach based on chi-squared distribution theory. Instead of using simple thresholding or moving averages, the system uses rigorous statistical bounds that guarantee 99.999% reliability while being computationally efficient through matrix operations
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method provides reliability of 99.999% accuracy for velocity and course over ground calculations, enabling their use in safety-critical systems by ensuring they do not exceed alert limits.
Implementation Method 1
The GNSS receiver utilizes phase range rate measurements (Doppler measurements) and variance measurements to calculate protection levels for velocity
Data Source
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AI summary
In an example embodiment, a GNSS receiver may calculate protection levels for velocity and course over ground computed at a GNSS receiver. Specifically, the GNSS receiver may obtain Doppler measurements and variance measurements based on satellite signals received from at least five GNSS satellites. The GNSS receiver may utilize a least squares method to calculate the velocity states (e.g., x-velocity state, γ-velocity state, and z-velocity state) and the clock bias for the GNSS receiver. The GNSS receiver may calculate the slope for each Doppler measurement on each velocity state. The GNSS receiver may then select the maximum slope for each velocity state and scale up the maximum slopes by a non-centrality parameter to calculate the protection level for each velocity state in the ECEF frame. The GNSS receiver may convert the velocity protection levels to NEU velocity protection levels to then calculate a protection level for course over ground.