GNSS Subcarrier Tracking Loops for False Lock Correction
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Solution Overview
Problem
Current tracking methods for BOC and MBOC signals in GNSS systems face challenges in accurately distinguishing between the main peak and side peaks of the autocorrelation function, leading to systematic errors and position inaccuracies due to false locks.
Innovation Solution
The proposed solution involves an alternative tracking algorithm utilizing early-minus-late (EML) and arctan discriminators in cooperative loops within a GNSS receiver, specifically in the subcarrier and delay lock loops, to enhance the detection and correction of false locks, thereby improving tracking accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If subcarrier modulation is used in BOC signals, then tracking accuracy is improved due to narrower main peak, but false lock to side peaks occurs causing systematic errors
Solution Approach 1:
The patent divides the tracking function into two independent but cooperative loops: a subcarrier lock loop for tracking the subcarrier signal and a delay lock loop for tracking the code signal. This segmentation allows each loop to focus on specific aspects of signal tracking, with the subcarrier loop providing accurate subcarrier phase tracking and the delay loop providing code delay tracking, thereby resolving the contradiction between achieving narrow main peak tracking and avoiding side peak false locks
Solution Approach 2:
The patent implements feedback mechanisms in both the subcarrier lock loop and delay lock loop, where the output of each loop feeds back to adjust its respective tracking parameters. The subcarrier loop feedback corrects subcarrier phase deviations, while the delay loop feedback corrects code delay deviations. This feedback ensures that the system continuously maintains accurate tracking and can detect and correct false lock conditions
2Device complexity
If conventional tracking methods are used, then system complexity is reduced, but ability to detect and correct false locks is insufficient
Solution Approach 1:
The patent merges the subcarrier tracking function and code tracking function into a unified tracking system with cooperative loops. The subcarrier lock loop and delay lock loop work together, with the subcarrier loop providing enhanced tracking accuracy and the delay loop providing code delay measurement. This merging allows the system to detect and correct false locks more effectively than conventional single-loop methods, while maintaining reasonable system complexity through efficient use of shared components
Data Source
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AI summary
An embodiment of the invention relates to a system (200) for tracking of a received signal s(t) with at least one subcarrier, wherein the received signal represents a carrier signal modulated with a code signal and modulated with a subcarrier signal, wherein the system comprises the following independent and cooperatively operating loops: a phase lock loop (201-203) for tracking the carrier signal, a subcarrier lock loop (206-208) for tracking the subcarrier signal, which comprises a first controllable oscillator (206) and a first early-minus-late discriminator (207) for generating a control signal for the first controllable oscillator, wherein the first early-minus-late discriminator (207) generates the control signal based on a difference between the correlation results with replica of an advanced subcarrier signal E and the replica of a delayed subcarrier signal L, and a delay lock loop (204-205, 209) for tracking the code signal, which comprises a second controllable oscillator (209) and a second arctan discriminator (204) for generating a control signal for the second controllable oscillator, wherein the second arctan discriminator (204) generates the control signal based on the correlation results with a replica of a prompt code signal P multiplied with a prompt subcarrier signal P, and a replica of a prompt subcarrier signal P multiplied with the difference of an advanced and a delayed code signal E-L.