Positioning Filter Initialization Using Non-Simultaneous Satellite Measurements
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Solution Overview
Problem
Mobile GPS receivers in harsh signal environments, such as urban areas, often struggle to acquire simultaneous signals from three satellites, leading to delayed or failed position determination due to the requirement for initial state information from multiple satellite vehicles, which degrades performance.
Innovation Solution
A method that seeds a positioning filter with an approximate position and updates it using measurements from less than three reference stations or pseudoranging sources across different measurement epochs, allowing for position estimation even in environments where simultaneous signals are not readily available, utilizing techniques like Kalman filters and back propagation to refine estimates over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the receiver requires simultaneous signals from three satellites to initialize the position solution, then the position determination accuracy is improved, but the time to first fix increases and the system fails in harsh signal environments
Solution Approach 1:
The system performs preliminary measurements and stores measurement data from fewer than three satellites before the formal position solution is initiated. This preliminary action allows the system to accumulate available data during the acquisition phase, so that when initialization occurs, the filter already has partial measurement history to work with, reducing the time to first fix while maintaining accuracy through the use of stored preliminary data in conjunction with subsequent measurements.
2Reliability
If the receiver requires simultaneous signals from three satellites for position solution, then the initial position estimate reliability is improved, but the system becomes unable to operate in urban environments with signal blockage
Solution Approach 1:
The system dynamically adapts its operation mode based on signal availability. When three simultaneous satellite signals are available, it operates in standard mode for high reliability. When fewer than three signals are available (as in urban canyons), it automatically transitions to a degraded mode that uses the positioning filter with preliminary measurements from fewer satellites, thus maintaining operational capability across varying environmental conditions while preserving reliability when possible.
Solution Approach 2:
The system changes the operational parameters of the positioning filter based on measurement availability. When preliminary measurements from fewer than three satellites are available, the system modifies the filter initialization parameters to accommodate this reduced data set, allowing the algorithm to function reliably with incomplete initial data rather than requiring the standard three-satellite minimum, thereby enabling operation in harsh environments.
3Measurement precision
If the system waits for three simultaneous satellite signals before initializing the Kalman filter, then the position solution accuracy is ensured, but the productivity and response time of the system deteriorates
Solution Approach 1:
The system performs preliminary measurements and stores measurement data from fewer than three satellites before the formal position solution is initiated. This preliminary action allows the system to accumulate available data during the acquisition phase, so that when initialization occurs, the filter already has partial measurement history to work with, reducing the time to first fix while maintaining accuracy through the use of stored preliminary data in conjunction with subsequent measurements.
Data Source
AI summary
A mobile communications device uses a method for determining position that involves a positioning filter, such as a Kalman filter, which is initialized with measurements from reference stations such as satellite vehicles and/or base stations which may be acquired during different epochs. Accordingly, the positioning filter may be used for position estimation without the need to first acquire at least three different signals during the same measurement epoch.