GNSS Subcarrier Signal Tracking Loop Design
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Solution Overview
Problem
Existing tracking methods for subcarrier modulated signals, such as BOC and MBOC, face challenges with false locks to side peaks in the autocorrelation function, leading to systematic errors in pseudo-range measurements and increased computational complexity.
Innovation Solution
A system and method that uses an Early-Late signal generation unit and a delay locked loop to generate and update delay estimates, exploiting subcarrier accuracy while reducing ambiguity and computational complexity, by generating replicas of the code and subcarrier signals with fixed phase relationships and using a single delay locked loop for precise delay estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple tracking loops are used to track each peak of the autocorrelation function, then tracking accuracy is improved, but device complexity increases
Solution Approach 1:
The patent merges multiple tracking functions into a single tracking loop by using a codeless delay lock loop that directly tracks the subcarrier phase. This eliminates the need for multiple separate tracking loops while maintaining the ability to achieve precise delay estimates through the subcarrier phase information.
Solution Approach 2:
The patent transitions from tracking in the code domain to tracking in the subcarrier phase domain. By using the subcarrier phase as the tracking variable instead of code phase, the system achieves precise delay estimation without requiring multiple tracking loops for each autocorrelation peak.
2Ease of operation
If conventional tracking methods are used, then implementation is straightforward, but false locks to side peaks occur leading to systematic errors
Solution Approach 1:
The patent extracts the subcarrier phase information from the received signal and uses it as the primary tracking variable. By focusing on the subcarrier phase rather than the entire autocorrelation structure, the method eliminates false locks to side peaks while maintaining implementation feasibility through a single tracking loop.
Solution Approach 2:
The subcarrier phase acts as an intermediary variable that provides unambiguous delay information. Instead of directly tracking the multi-peaked autocorrelation function, the system uses the subcarrier phase as an intermediate representation that uniquely identifies the signal delay without false peaks.
3Measurement precision
If subcarrier modulated signals are used, then tracking accuracy is improved, but subcarrier ambiguity increases leading to false locks
Solution Approach 1:
The patent implements a feedback mechanism in the codeless delay lock loop where the estimated subcarrier phase is continuously refined based on the error signal. This feedback ensures that the tracking remains locked to the correct main peak and prevents drift to false peaks, thereby resolving the subcarrier phase ambiguity.
Data Source
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AI summary
The present document relates to the reception of subcarrier modulated signals, such as Binary Offset Carrier (BOC) modulated signals. In particular, the present document relates to the reception of subcarrier modulated navigation signals in a Global Navigation Satellite System (GNSS). A system (200) configured to determine a delay estimate τ̂ of a delay incurred by a navigation signal (220) is described. The navigation signal (220) is indicative of a carrier signal modulated with a code signal and modulated with a subcarrier signal (101). The system (200) comprises an Early-Late signal generation unit (202) configured to generate an EP signal (232), a LP signal (233), a PE signal (235) and a PL signal (234) based on the code signal, based on the subcarrier signal (101) and based on a first delay estimate τ̃. Furthermore, the system (200) comprises a delay locked loop (202, 203-4, 203-5, 204-4, 204-5, 207, 208) configured to determine the first delay estimate τ based on the received navigation signal (220), the EP signal (232) and the LP signal (233). In addition, the system (200) comprises a detection path (202, 203-1, 203-2, 204-1, 204-2, 209, 210 211) configured to determine a delay offset based on the received navigation signal (220), the PE signal (235) and the PL signal (234). The system (200) is configured to determine the delay estimate τ̂ based on the first delay estimate τ̃ and based on the delay offset.