GNSS Receiver Time Counter Offset Management
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Solution Overview
Problem
GNSS receivers face the week number roll-over problem due to limited data length for time information, leading to incorrect date determination and position calculation, particularly evident in GPS systems with 10-bit week number representation, which results in date jumps every 19.7 years.
Innovation Solution
Implementing a dynamically varying offset variable stored in non-volatile memory, allowing for periodic updates to correct the time information and mitigate the roll-over issue by performing remainder division and threshold-based updates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a static offset value is used in firmware to reconstruct the week number from GPS-LNAV messages, then the date determination is corrected for the current period, but the system will again determine an incorrect date after 1023 weeks
Solution Approach 1:
The patent transforms the static offset value stored in firmware into a dynamic offset variable that can be updated at runtime. The offset is initially read from firmware but can be modified during operation when a more accurate time source becomes available, extending the system's reliable operation beyond the 1023-week limitation
Solution Approach 2:
The patent performs preliminary action by reading the offset value from firmware in advance and storing it in a variable. This allows the system to immediately use the offset for date reconstruction while maintaining the capability to update it later when better time information becomes available
2Reliability
If the offset variable is updated frequently to maintain accuracy, then the date determination remains correct longer, but the writing operations to non-volatile memory increase
Solution Approach 1:
The patent implements periodic action by updating the offset variable only when specific conditions are met (difference exceeds threshold or synchronization events occur), rather than continuously. This reduces unnecessary memory write operations while maintaining date determination accuracy
Solution Approach 2:
The patent uses parameter changes by introducing a threshold value that controls when updates occur. The offset is only updated when the time difference exceeds this threshold, optimizing the balance between maintaining accuracy and reducing memory operations
Data Source
AI summary
A method for providing time information in a GNSS receiver includes receiving at least one time counter variable from a GNSS satellite. The at least one time counter variable describes a number of time intervals that have passed since a time start value, and a data length of the time counter variable limited to a maximum number of countable time intervals. The method also includes reading an offset variable out of a non-volatile memory held in the GNSS receiver. The offset variable describes a time previously received and reconstructed by the GNSS satellite, and a data length of the offset variable exceeds the data length of the time counter variable. The method further includes carrying out a remainder division of the offset variable with a maximum number given by the data length of the at least one time counter variable in order to determine an offset time counter variable.