Pseudo Maximum Likelihood Tracking for GNSS Receivers
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Solution Overview
Problem
Conventional GNSS receivers face challenges in accurately determining the receiver state due to limitations in tracking individual satellite signals and modeling the probability distribution of the receiver state, leading to reduced accuracy and resilience to interference and multipath effects.
Innovation Solution
The method involves generating correlation grids from received positioning signals from multiple satellites, estimating the probability distribution of the receiver state, and determining a maximum likelihood estimate using a navigation processor, which simplifies the tracker architecture and combines information from all visible satellites for improved accuracy and reacquisition.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional tracking methods are used to determine receiver state, then the tracker architecture is simpler, but the accuracy and resilience to interference and multipath effects deteriorates
Solution Approach 1:
The patent segments the tracking function into two independent components: a correlation engine that generates correlation grids for each satellite without tracking, and a navigation processor that estimates probability distribution and determines receiver state. This segmentation allows each component to be optimized independently, improving accuracy while managing complexity.
Solution Approach 2:
The patent introduces correlation grids as an intermediary data structure between the correlation engine and navigation processor. These grids contain correlation values at multiple hypotheses and serve as the medium for transferring information, enabling the navigation processor to perform probabilistic analysis without direct access to raw satellite signals.
2Reliability
If individual satellite signals are tracked separately, then the tracking process is simpler, but the resilience to multipath interference and signal occlusion deteriorates
Solution Approach 1:
The patent merges information from multiple satellites into a unified probability distribution estimate at the navigation processor. By combining correlation grids from all visible satellites and performing joint probability analysis, the system achieves improved reliability and resilience to individual satellite failures or interference.
Solution Approach 2:
The patent changes the fundamental parameter being tracked from individual satellite signal parameters to the probability distribution of the receiver state. This parameter transformation allows the system to evaluate multiple hypotheses simultaneously and select the most likely receiver state, improving resilience to multipath and occlusion.
3Productivity
If full correlation function is used for tracking, then the accuracy and reacquisition performance improves, but the processing complexity increases
Solution Approach 1:
The patent performs preliminary correlation computations across the full correlation function and stores results in correlation grids before navigation processing. This preliminary action allows the system to have all correlation information readily available for rapid probability distribution estimation and reacquisition without performing computationally intensive operations during critical tracking phases.
Data Source
AI summary
GNSS receivers and methods of determining a current receiver state of a GNSS receiver are provided. The method includes receiving positioning signals from a plurality of satellites; generating a plurality of correlation grids from the received positioning signals, where each correlation grid is associated with a respective one of the plurality of satellites; estimating a probability distribution of the current receiver state from the plurality of correlation grids; and determining a maximum likelihood estimate of the current receiver state from the estimated probability distribution.