Mobile Device Positioning Without Week Number Extraction
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Solution Overview
Problem
Existing GPS positioning methods require knowledge of the week number, which increases the time to first fix during a cold start, as it needs to be extracted from satellite signals, leading to prolonged delays due to the complexity and time-consuming calculations involved in determining pseudoranges and receiver clock offset.
Innovation Solution
A method that allows for determining the position of a mobile device without prior knowledge of the week number by using stored satellite trajectory data to derive satellite positions, reducing the time to first fix by extracting only the time of week from satellite signals, and iteratively solving a system of equations for device parameters using measured pseudoranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the week number is extracted from satellite signals before position determination, then the position can be determined with accurate timing, but the time to first fix increases by up to 30 seconds
Solution Approach 1:
The method performs preliminary action by using stored satellite trajectory data to calculate expected week numbers before actually receiving satellite signals. This allows the receiver to have a head start in determining the correct week number without waiting for satellite transmission, thereby reducing the time to first fix while maintaining position determination accuracy
Solution Approach 2:
The method creates a copy of satellite trajectory information by storing ephemeris data and almanac data locally in the receiver. This local copy allows the receiver to independently calculate satellite positions and determine week numbers without requiring real-time satellite signal transmission, thus reducing delays
2Loss of time
If satellite trajectory data is stored in the mobile device, then the time to first fix is reduced, but the device complexity increases
Solution Approach 1:
The satellite trajectory data is segmented into two parts: ephemeris data for precise short-term positioning and almanac data for long-term approximate positioning. This segmentation allows the receiver to use different data sets depending on the situation, reducing the overall complexity while maintaining fast time to first fix capability
Solution Approach 2:
The method changes the parameter of data precision by using high-precision ephemeris data when available for rapid initial positioning, then transitioning to lower-precision almanac data for long-term operation. This parameter change allows the system to maintain fast time to first fix without permanently requiring large amounts of high-precision data
Data Source
AI summary
A set of device parameters consisting of clock bias and position of a mobile device is determined without previous knowledge of the week number (WN) in that solutions of a set of equations derived from a least squares type weight function involving pseudoranges related to the device parameters via basic equations are attempted with a time of week (TOW) extracted from satellite signals and various week number candidates. A solution algorithm which iteratively solves the set of equations is used, each iteration step involving a linearisation of the latter and resulting in corrections of the device parameters. After elimination of week numbers where the solution algorithm does not yield a solution a valid week number is selected from the remaining week numbers in that a deviation value is determined which reflects differential terms, i.e., differences between pseudorange values as measured and as derived from the set of device parameters according to the solution, e.g., by evaluation of the weight function. The week number yielding the smallest deviation value is selected. If the week number is confirmed by various checks the device parameters according to the corresponding solution are used, e.g., displayed, by the mobile device.