GPS Receiver Location Determination Using Almanac Data
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Solution Overview
Problem
GPS receivers struggle to accurately determine location when fewer than four GPS satellites are visible due to interference or obstructions, as they require signals from at least four satellites to function effectively.
Innovation Solution
A GPS receiver system that includes a GPS receiving unit, a decoder, a database, and a navigation filter, which allows the selection of visible satellite candidates using time and almanac information to calculate pseudo-ranges and determine location even when fewer than four satellites are visible, employing geometric trigonometry for positioning calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If GPS receiver requires signals from at least four GPS satellites to determine location, then location determination accuracy is improved, but reliability deteriorates when fewer than four satellites are visible due to interference or obstructions
Solution Approach 1:
The system performs preliminary actions by pre-acquiring and storing almanac information and satellite disposition data for all satellites in the GPS constellation before actual positioning is needed. This advance preparation enables the receiver to quickly identify and utilize visible satellite candidates even when fewer than four satellites are currently visible, thereby maintaining reliability without sacrificing accuracy
Solution Approach 2:
The system creates a virtual model of the GPS satellite constellation using stored almanac information and satellite disposition data. This copied representation allows the receiver to calculate pseudo-ranges to visible satellite candidates as if receiving actual signals, enabling location determination to proceed reliably even when physical signal reception is limited to fewer than four satellites
2Reliability
If GPS receiver uses additional satellites beyond visible ones, then location determination reliability is improved, but device complexity increases due to additional calculations
Solution Approach 1:
The system changes the parameter set used for positioning calculations by incorporating satellite disposition information and almanac data alongside actual pseudo-range measurements. This parameter expansion allows the mathematical model to accommodate scenarios with fewer than four visible satellites while maintaining solution reliability, and the complexity increase is managed through efficient use of pre-computed satellite ephemeris data
Data Source
AI summary
A Global Positioning System (GPS) receiver includes a GPS receiving unit configured to receive navigation data from at least one visible satellite, a decoder configured to decode the received navigation data to extract time and almanac information from the decoded navigation data and a database configured to store satellite disposition information. A satellite location determining unit is configured to select at least one visible satellite candidate using the time information and the satellite disposition information, and to determine locations-in-space of the at least one visible satellite candidate with the almanac information. Also, a navigation filter is configured to calculate pseudo-ranges from the at least one visible satellite and the selected at least one visible satellite candidate using the corresponding locations-in-space, and to determine a location of the GPS receiver using the calculated pseudo-ranges.