GPS Receiver Coherent Correlation Weak Signal Acquisition
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional GPS receivers face challenges in achieving sufficient sensitivity in weak signal environments, such as indoors and downtown areas, due to the 'squaring loss' from non-coherent combination of GPS signal correlations, which reduces their ability to acquire and track GPS signals effectively.
Innovation Solution
The method involves using assistance data to predict navigation data and Doppler shifts, synchronizing the GPS receiver's clock, and employing coherent correlation techniques to enhance sensitivity, allowing for accurate code phase acquisition and position calculation even in weak signal conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If non-coherent combination of GPS signal correlations is used, then device complexity is reduced, but sensitivity deteriorates due to squaring loss
Solution Approach 1:
The patent applies preliminary action by using assistance data to predict navigation data and Doppler shifts before the actual signal acquisition process. This pre-computation of expected signal characteristics allows the receiver to focus its correlation efforts more precisely, enabling coherent combination methods to achieve better sensitivity without requiring excessively complex processing. The predicted data prepares the system in advance to handle weak signals more effectively.
2Adaptability or versatility
If two dimensional search process is conducted for each GPS signal, then all visible satellites can be identified, but acquisition time increases due to checking each C/A code with every possible code phase and Doppler frequency
Solution Approach 1:
The patent uses assistance data containing predicted navigation data and Doppler shifts to pre-determine the search space for signal acquisition. Instead of conducting a exhaustive two-dimensional search across all possible code phases and Doppler frequencies, the receiver uses the predicted information to narrow down the search to only the most likely parameters. This dramatically reduces acquisition time while still ensuring all visible satellites can be identified.
Solution Approach 2:
The patent applies local quality by concentrating computational resources on the specific regions of the search space where signals are most likely to be found, based on predicted navigation data and Doppler shifts. Rather than uniformly searching all possible parameters, the system focuses its correlation efforts on locally optimized search regions, improving efficiency without sacrificing the ability to identify all visible satellites.
3Reliability
If coherent correlation techniques are employed to enhance sensitivity, then signal acquisition performance improves in weak signal conditions, but device complexity and computational requirements increase
Solution Approach 1:
The patent reduces coherent correlation complexity by using assistance data to predict navigation data and Doppler shifts in advance. These predictions allow the receiver to pre-configure correlation parameters and focus computational effort on specific, predicted signal characteristics rather than performing exhaustive coherent correlation across all possible parameters. This maintains the sensitivity benefits of coherent correlation while reducing the computational burden.
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 significantly improves the sensitivity and speed of GPS signal acquisition, enabling precise positioning in challenging environments by reducing the search space for Doppler frequencies and allowing coherent correlation, thus enhancing the GPS receiver's performance in weak signal scenarios.
Implementation Method 1
converting the GPS signal to an intermediate frequency (IF) signal
Implementation Method 2
correlating the IF signal with the predicted navigation data, the local carrier signal and the local pseudorandom code
Implementation Method 3
GPS signals from different satellites travel through different channels and are shifted in frequency due to the relative receiver-satellite motion. This is the so-called Doppler shift
Data Source
AI summary
The present invention is a method for GPS positioning in a weak signal environment. The method includes obtaining assistance data for a GPS signal from a satellite at a predetermined time, wherein the assistance data including predicted navigation data, Doppler shift and Doppler shift rate and the GPS signal being modulated by a carrier signal, a pseudorandom code and navigation data, estimating a predicted receiving time for the GPS signal reaching the GPS receiver, capturing the GPS signal, converting the GPS signal to an intermediate frequency signal, acquiring a code phase of the pseudorandom code from the intermediate frequency signal by using the assistance data and the predicted receiving time, and obtaining a position for the GPS receiver based on the predicted navigation data and the code phase of the pseudorandom code. To acquire the code phase of the pseudorandom code, the GPS receiver corrects a real time clock to one millisecond accuracy and process the intermediate frequency signal through coherent correlation of one second.