GNSS Receiver Multipath Signal Detection via Asymmetric Autocorrelation
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Solution Overview
Problem
GNSS receivers face challenges in accurately determining position due to multipath signal components, which cause errors in position determination, especially in environments with significant reflections such as urban areas or railway applications.
Innovation Solution
A method that analyzes the autocorrelation function values of GNSS code signals to detect and exclude signals affected by multipath components by subtracting bias values from undistorted signals, using asymmetrically chosen functional values and higher-order metrics to enhance multipath detection and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multipath signal components are present in the received GNSS code signal, then the GNSS receiver can still receive signals in reflective environments, but errors in position determination occur due to shifted autocorrelation function maximum
Solution Approach 1:
The patent applies preliminary action by analyzing multiple function values of the autocorrelation function at different discrete chip spacings before determining the position. By evaluating the autocorrelation function at multiple predetermined chip spacings (not just at the maximum), the system can detect multipath effects in advance and exclude affected signals from position calculation, thereby preventing position determination errors.
Solution Approach 2:
The patent replaces the traditional mechanical approach of simply taking the autocorrelation maximum as the time delay measure with a signal processing substitution. Instead of relying on the physical maximum point, the system uses a test metric based on multiple autocorrelation function values to identify and exclude multipath-affected signals, substituting the mechanical maximum-seeking approach with a computational validation process.
2Productivity
If the maximum of the autocorrelation function is used to determine the prompt chip spacing, then the time delay can be obtained quickly, but multipath signal components may shift the maximum causing position determination errors
Solution Approach 1:
The patent applies preliminary action by pre-evaluating the autocorrelation function at multiple predetermined chip spacings before final position determination. This allows the system to quickly identify which signal paths are affected by multipath through the test metric, excluding them before the actual position calculation, thus maintaining both speed and accuracy.
Solution Approach 2:
The patent introduces an intermediary test metric that acts as a mediator between the raw autocorrelation function and the final position determination. This test metric, based on multiple function values at different chip spacings, filters out multipath-affected signals before they can corrupt the position calculation, serving as an intermediary validation layer.
3Measurement precision
If more satellites are used for position determination, then the position accuracy can be improved, but multipath-affected signals from additional satellites may introduce more errors
Solution Approach 1:
The patent introduces an intermediary test metric that validates each satellite signal before inclusion in position determination. This intermediary layer checks the autocorrelation function values at multiple chip spacings and excludes signals that fail the test, allowing the system to safely use more satellites for improved accuracy while filtering out multipath-affected signals.
Solution Approach 2:
The patent applies feedback by using the test metric results to control which satellite signals are included in position determination. The system continuously monitors the autocorrelation function values and uses this feedback to exclude problematic signals, creating a closed-loop system that maintains accuracy even when processing signals from multiple satellites in reflective environments.
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AI summary
A method for operating a GNSS (=Global navigation satellite system) receiver (12), wherein for a position determination, the GNSS receiver (12) receives from a multitude of satellites (10) a respective GNSS code signal (30), and wherein for each signal (11) from a satellite (10), the received GNSS code signal (30) is correlated with a reference code signal (31) generated by the GNSS receiver (12) to obtain an autocorrelation function (70), wherein a multitude of function values (Ai) of the autocorrelation function (70) at different discrete chip spacings (Pi) are analyzed and used in obtaining a test metric (TM), is characterized in that using the test metric (TM), a decision is made whether the received GNSS code signal (30) is suitable for a position determination or unsuitable for a position determination due to multipath signal components, that a position determination of the GNSS receiver (12) is made based on the received GNSS code signals (30) from the multitude of satellites (10), with received GNSS code signals (30) considered unsuitable for position determination being excluded from the position determination, that the chip spacings (Pi) of the multitude of function values (Ai) of the autocorrelation function (70) are chosen asymmetrically with respect to a prompt chip spacing (P0), that during analysis of the multitude of function values (Ai) of the autocorrelation function (70), a bias removal is performed, taking into account corresponding function values of an autocorrelation function (60) that would result from a received GNSS code signal (30) of the satellite (10) unaffected by multipath signal components, and that the multitude of function values (Ai) contribute to the test metric (TM) in an order higher than first order. The invention provides a simple method for operating a GNSS receiver, which minimizes errors in position determination caused by multipath signal components.