GNSS Receiver Doppler Estimation for Dynamic Signal Tracking
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Solution Overview
Problem
Existing GNSS receivers face challenges in maintaining sensitivity and accuracy under dynamic conditions, particularly when trying to increase coherent integration time, which can lead to signal loss due to sudden acceleration.
Innovation Solution
The method involves using Doppler estimates derived from inertial measurements to compensate for motion, allowing for longer coherent integration times while maintaining signal lock. This is achieved by initializing and updating the carrier phase of a local carrier signal based on first and second Doppler estimates, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coherent integration time is increased to improve receiver sensitivity, then the ability to detect weak LoS signals is improved, but the system becomes more susceptible to signal loss under dynamic conditions such as sudden acceleration
Solution Approach 1:
The system performs preliminary actions by predicting carrier phase using Doppler estimates from inertial measurements before the actual signal processing occurs. This allows the receiver to pre-compensate for expected motion effects during the coherent integration period, enabling longer integration times without losing signal lock during dynamic conditions.
Solution Approach 2:
The patent introduces an intermediary mechanism - a buffer storing past signal samples and an inertial measurement unit (IMU) - that mediates between the incoming GNSS signal and the local carrier signal generation. The IMU provides intermediate Doppler estimates that bridge the gap between actual signal characteristics and the local carrier, allowing accurate phase compensation even during rapid motion changes.
2Measurement precision
If coherent integration time is increased to reject multipath signals, then the accuracy of ranging measurements is improved, but the system becomes more vulnerable to acceleration effects that corrupt calculations
Solution Approach 1:
The system implements feedback by continuously monitoring inertial measurements and using them to update Doppler estimates in real-time. These updated estimates feed back into the carrier phase prediction and local carrier signal generation, creating a closed-loop system that actively compensates for acceleration effects throughout the coherent integration period, thereby maintaining measurement accuracy.
Solution Approach 2:
The patent dynamically changes parameters by adjusting the carrier phase prediction based on varying Doppler estimates from the IMU. As acceleration conditions change, the system modifies the predicted phase parameters in real-time, allowing the coherent integration to maintain accuracy despite changing motion conditions that would otherwise corrupt the measurements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the receiver's sensitivity and ability to track GNSS signals in challenging environments, even under dynamic conditions, by effectively mitigating the effects of motion on coherent integration.
Implementation Method 1
mixing a local carrier signal with a plurality of the samples to generate a plurality of mixed signal samples
Implementation Method 2
A first Doppler estimate is derived from a measurement gathered in a previous epoch
Data Source
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AI summary
A method and apparatus are provided for processing a GNSS signal received at a receiver. A carrier phase of a local carrier signal is initialised for the current epoch based on a first Doppler estimate. The first Doppler estimate is derived from a measurement gathered in the previous epoch. The carrier phase is updated repeatedly for the current epoch while the GNSS signal is being mixed with the local carrier signal. The updating relies on second Doppler estimates, which are based on inertial measurements made at the receiver.