GPS Navigation Signal Error Correction Using Verification Words
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Solution Overview
Problem
In weak field environments, GPS satellite signals with BPSK modulation are prone to demodulation errors, leading to incorrect data reception and increased Time to First Fix (TTFF) due to inefficient error detection methods, where one demodulation error can result in all subsequent data being incorrect.
Innovation Solution
A method involving error detection using a check code and verification word table to identify and correct demodulation errors by inverting bit values subsequent to the estimated error origin, ensuring accurate data recovery and reducing TTFF.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If error detection is performed using conventional methods in weak field environments, then demodulation errors can be detected, but all subsequent data becomes incorrect and must be discarded, causing increased TTFF
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing verification words for each possible error position in a verification word table before actual signal reception. When an error occurs, the system can immediately lookup the verification word and identify the error position without time-consuming calculations, enabling rapid correction and reducing TTFF while maintaining data accuracy
Solution Approach 2:
The patent introduces verification words as an intermediary element between error detection and correction. These verification words serve as a mediator that bridges the gap between detecting an error and identifying its specific position, allowing the system to efficiently locate and correct errors without discarding entire data sets, thus reducing time loss while preserving reliability
2Reliability
If one demodulation error occurs in BPSK modulated GPS signals, then all subsequent demodulated data becomes incorrect, but conventional error detection discards the entire data set
Solution Approach 1:
The patent applies segmentation by dividing the error correction process into distinct segments: error detection using verification words, error position identification through table lookup, and selective bit inversion correction. This segmentation allows the system to handle errors locally rather than discarding entire data sets, improving data collection efficiency while maintaining error detection capability
Solution Approach 2:
The patent changes the parameter approach from binary (error detected/discarded) to granular (error position identified/bit-by-bit correction). By using verification words to identify specific error positions and correcting only the affected bits through inversion, the system transforms the error handling parameter from all-or-nothing to precise and selective, thereby improving productivity while maintaining reliability
Data Source
AI summary
A demodulation unit demodulates a received signal in which carrier wave of a navigation message that is modulated according to a BPSK modulation scheme are included. An error detection processing unit performs an error detection process on the demodulation result using an error detection bit that is included in the demodulation result. A verification word generator generates a verification word using the demodulation result and a check code when an error is detected by the error detection process, the check code being determined in advance for each bit of the navigation message based on a predetermined encoding rule. An estimation unit estimates an originating bit of a demodulation error by comparing the verification word generated by the verification word generator with a verification word table stored in a storage unit. A correction unit corrects the demodulation result by inverting the bit values of bits subsequent to the estimated originating bit.